Local Group Dwarf Galaxies: Searching for Reionization Traces in the Star Formation History
We present results of the LCID (Local Cosmoly from Isolated Dwarfs) project. The main purpose of the project is to obtain the star formation histories (SFHs) of a sample of dwarf galaxies with three objectives: (i) searching for signatures of cosmic reionization and local feed-back on the star formation history (SFH); (ii) searching for any SFH-morphological type relation, and (iii) searching for stellar population gradients and their temporal evolutions as signature of the galactic evolution. Six isolated dwarfs have been observed during 133 orbits with the ACS@HST. The SFHs of all them have been derived from the on-set of the star formation, more than 13 Gyr ago, with a precission better than 1 Gyr for the whole history. Here we present and discuss the effects of UV-background due to cosmic reionization on the SFH and the consequences that our results may have on the standard scenario of galaxy formation.
The formation of Lenticular (S0) Galaxies
Evidence is mounting indicating that S0s were once spiral galaxies that ceased forming stars and subsequently changed their morphology. Studying the timing, location and physical mechanism(s) involved in this transformation is not only interesting in itself, but it can also provide very useful clues on how galaxies evolve and the possible role of the environment. During the last few years we have been following several lines of research to test whether this transformation is indeed taking place, find out where it happens, and look for the physics driving it. At low redshift we have studied in detail the final products of the transformation - the S0s themselves - while at intermediate redshifts (z~0.5) we have concentrated on the putative progenitors - spiral galaxies - and the galaxies caught in the act of transforming. In this talk I present some of our more interesting results. Although there are still some loose ends, a coherent picture may be emerging.
Stellar Populations across Cosmic Times
TBD
Massive stars in galaxies - what stars ionize He II?
The stellar populations of galaxies are our main probes of the galaxy's content and while low mass stars set the total mass of stars in a galaxy, the short lived massive star dominate the energetics but do we understand the properties of these stars? Here we report on the largest, systematic study of star-forming galaxies with nebular He II emission. This line is a sensitive probe of the far-UV spectral energy distribution of massive stars and it has long been agreed that this line is primarily excited by Wolf-Rayet stars. In this study we are for the first time able to test this assumption in a systematic manner, and we show that there is a clear trend that low metallicity galaxies showing nebular He II have no visible traces of Wolf-Rayet stars. What then is producing the necessary hard photons? We discuss a few possibilities.
The Formation History of the Ultra-Faint Dwarf Galaxies
We present initial results from an HST survey of the ultra-faint dwarf galaxies. These Milky Way satellites were recently discovered in the Sloan Digital Sky Survey, and appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in the efforts to understand the missing satellite problem. Because they are the least luminous, most dark matter dominated, and least chemically evolved galaxies known, the ultra-faint dwarfs are the best candidate fossils from the early universe. The primary goal of the survey is to measure the star-formation histories of these galaxies and discern any synchronization due to the reionization of the universe.
PS Models: a promising future in the study of the distant past
Recent advances in the fields of stellar evolution, stellar model atmospheres, and stellar spectral libraries, allow us to build more realistic stellar population synthesis models. Applications of these models to problems of current interest are discussed. Problems that still need to be understood and data sets that need to be collected in order to solve issues present in these models are listed. In particular, I will show tests of the capability of current stellar population synthesis models that incorporate a state-of-the-art description of the evolution of stars in the TP-AGB to reproduce the luminosity function of these stars derived from the SAGE survey of the LMC and SMC.
Stellar Populations at the Highest Redshifts
I will discuss HST searches for star forming galaxies at very high redshift, z>6, within the epoch of reionization (the first billion years). Many of these galaxies exhibit very blue colours in the rest-frame ultraviolet, indicating low dust and metallicity and potentially a top-heavy initial mass function. For a subset, Spitzer detections allow us to fit stellar population synthesis models and estimate the mean stellar age and stellar mass. I will review future prospects with JWST and Extremely Large Telescope to address the ages, metallicities, IMFs and dust content of high redshift galaxies.
SED Fitting with CIGALE and Stellar Populations in Herschel LBGs at 2.5 < z < 4.0
We have selected in the 2-deg2 COSMOS field a sample of Lyman Break Galaxies in the redshift range 2.5 < z < 4.0. Part of this sample (~ 100) is detected in Far-InfraRed/Submm with Herschel. Another one is detected at 24um with Spitzer. The vast majority of them is undetected in IR but we do have their HST morphology. Moreover, the COSMOS field have been observed in a set of intermediate bands by the SUBARU telescope. We developed CIGALE to analyse the Spectral Energy Distributions (SEDs) of galaxies from the far-ultraviolet to the sub-millimeter range. We allow up to two stellar populations with different dust attenuation plus an AGN. The baseline ultraviolet dust attenuation law is Calzettti's one but we can add a bump and change the slope. We have used CIGALE to model these LBGs, compare their stellar population and dust properties and to identify any differences between them. The dusty LBG sample bears a number of common characteristics with the so-called sub-mm galaxies (SMGs). In this talk, we will briefly present the characteristics of CIGALE, present the LBG sample and try to place and classify these different types of galaxies in a global scheme of galaxy evolution.
Self Regulated Star Formation in High-z versus Low-Z Disk Galaxies
It seems to be clear by now that the star formation rate of disk galaxies at low and high redshifts is a boundary condition, determined by the amount of gas that is accreted onto a galaxy, averaged over a star formation timescale. This star formation timescale is however determined by stellar feedback and cooling that regulates the interaction between the various gas phases and their interaction. I will summarize new numerical simulations of star-forming and gas accreting disk galaxies that provide very detailed insight into the self-regulated evolution of star forming disk galaxies at low and high cosmic redshifts.
The spectral energy distributions of 24 micron galaxies at z>1 revisited
I will present a revised analysis of the spectral energy distributions (SEDs) of 24 micron galaxies at z>1. My aim is investigating whether and when the inclusion of an AGN component significantly improves the SED fitting at rest wavelengths < 2 microns, and is necessary to properly derive the stellar properties of the host galaxies.
Which environment affects galaxy evolution?
Using new data from the ZENS survey, comprising detailed observations of ~2000 galaxies in ~150 groups at z = 0.06, I compare, at constant galaxy stellar mass, how key galactic evolutionary diagnostics depend, when appropriate separately for central and satellite galaxies, on three different measures of environment, namely: (1) the mass of the host group halos; (2) the projected distance from the center of the halo; and (3) the filamentary large-scale structure density on which the groups reside. Specifically I show the dependence of - bulge and disk colors and color gradients, - key structural parameters such sizes of whole galaxies and of their bulges and disks, - the corresponding mass-radius relations, and - central-satellite and satellite-satellite merger rates, on these measures of environment. I compare these observational results with stellar population synthesis and semi-analytic models of galaxy formation, and conclude by presenting a global picture of how the different environments affect galaxy properties which is consistent with the observations above.
Constraints on galaxy physical properties from multi-wavelength observations
TBD
Elliptical galaxies across cosmic times
Despite the theoretical and observational progress, it is still difficult to draw a conclusive scenario on how elliptical galaxies formed and evolved. I will review the main developments in this field by focusing on the puzzling properties of ellipticals at cosmological distances and on the key open questions. I will also discuss the possibility to use these galaxies as tracers of the Universe expansion rate.
The stellar population of the Magellanic system with the VMC survey
The VISTA survey of the Magellanic system (VMC; PI Cioni) provides a new near-IR look at the stellar population of these nearby interacting galaxies. VMC observations began in 2009 and the survey is at present 21% complete with the first data already released to the astronomical community. The unprecedented sensitivity and spatial resolution in the near-IR as well as multi-epoch observations in the Ks band represent an asset for determining the spatially resolved history of star formation and for using variable stars to measure the distance and the geometry of the system. In this presentation I plan to describe briefly the VMC survey and to show recently published results on the star formation history, variable stars and extended objects as well as preliminary results on background quasars and proper motion.
Galaxy evolution through resolved stellar populations in the nearby CenA group.
The CenA/M83 group is a nearby dense complex (~4Mpc) dominated by a giant elliptical and a giant spiral, hosting more than 60 dwarf companions with a variety of morphological types and stellar contents. We study the resolved stellar populations of a sample of dwarfs using optical and near-infrared data from ACS/HST and ISAAC/VLT. We characterize their recent star formation histories and metallicity content, and compare them to what is known for Local Group dwarfs, underlining similarities and differences. Our results probe the fundamental interplay between nature and nurture in the evolution of dwarfs in such a dense environment. We furthermore present the results of the first deep survey of the resolved stellar populations in the remote outer halo of our nearest giant elliptical, CenA (VIMOS/VLT optical data). Tracing its halo structure (radial profile, extent and metallicity) out to a remarkable ~14 Reff and comparing the halo stellar populations to those of CenA's dwarf companions enables us for the first time to constrain the mechanisms that contributed to the build-up of CenA in the context of cosmological galaxy formation models.
SLUG - Stochastically Lighting Up Galaxies
The effects of stochasticity on the luminosities of stellar populations are an often neglected but crucial element for understanding populations in the low-mass or the low star formation rate regime. To address this issue, we developed SLUG, a new code to ""Stochastically Light Up Galaxies."" SLUG synthesizes stellar populations using a Monte Carlo technique that properly treats stochastic sampling including the effects of clustering, the stellar initial mass function, star formation history, stellar evolution, and cluster disruption. This code produces many useful outputs, including (1) catalogs of star clusters and their properties such as their stellar initial mass distributions and their photometric properties in a variety of filters, (2) two dimensional histograms of color-magnitude diagrams of every star in the simulation, and (3) the photometric properties of field stars and the integrated photometry of the entire simulated galaxy. We find that the previously neglected effects of clustering dramatically increase the scatter in observed photometric properties of stellar populations. For example, the Halpha luminosity can have over an order of magnitude higher scatter than if estimated assuming no stellar clustering. We also demonstrate that effects of stochasticity can mimic variation in the stellar IMF and confirm that observations of low star formation rate dwarf galaxies are actually consistent with a canonical IMF contrary to conclusions of some recent studies. SLUG is publicly distributed through the Web site http://sites.google.com/site/runslug/.
Reproducing galaxy evolution observables in a two star formation mode framework
I will report our ongoing work to describe the cosmic evolution of star forming galaxies in a simplified but efficient scenario where the main ingredient is the distinction and coexistence of two different modes of star formation: a disk mode and a starburst mode.
The Recent Star-forming History of the M31 Disk
The results of a MegaCam survey of the disk of M31 are presented. Main sequence stars with ages less than 200 Myr are resolved throughout most of the disk, and the luminosity function of main sequence stars is used to probe the recent star-forming history. We find that (1) the 10 kpc ring contains stars with ages of at least 100 Myr, and (2) the star formation rate throughout much of the disk has increased by a factor of 2 - 3 during the past 10 Myr. We also find that the number density of bright evolved stars to the NE of the galaxy center is higher than to the SW of the galaxy center, suggesting that this is a fossil star-forming region that dates to intermediate epochs.
Rotation of early type galaxies in high density environments
In the ATLAS-3D survey of a local volume the fraction of early-type galaxies found to be slow rotators increases by a factor of five from the field to the core of the Virgo cluster. We have started an exploration of the slow rotator fraction in higher density clusters. I report the results of integral field spectroscopy measurement of the internal kinematics of early-type galaxies in the Coma cluster, using the SWIFT instrument and in Abell 1689 (z=0.18) using the FLAMES instrument. Preliminary indications are that the slow rotator fraction in Coma, a factor of ten higher in density than the Virgo cluster, is at least as high, whereas in Abell 1689, a further factor of three higher in galaxy density than Coma, has a slow rotator fraction similar to that of whole ATLAS-3D sample. I will discuss the influence of galaxy selection on these results as well as contrasting the cluster morphology and the shape distribution of galaxies in these clusters. In the context of these results I will speculate on the factors that might determine the slow rotator fraction.
Star formation and stellar populations at the peak era of galaxy growth
The redshift range 1 < z < 3 spans the "boom years" of galaxy growth, when star formation and black hole accretion were at their peak, massive galaxies were evolving rapidly, and the Hubble Sequence was coming into being. I will discuss new insights into star formation, stellar populations, and dust obscuration in galaxies at that key epoch, drawing on an influx of valuable new data, including the deepest far-infrared surveys with Herschel and near-infrared imaging with the HST WFC3 in the GOODS and CANDELS fields.
Stellar populations in the outermost regions of massive galaxies
The mass assembly of galaxies leaves various imprints in their surroundings, such as shells, streams, tidal tails, extended halos, etc... The frequency and properties of the fine structures depend on the mechanism driving the mass assembly. Depending on whether massive galaxies, were formed through a monolithic collapse, rapid cold-gas accretion followed by violent disk instabilities, minor mergers or major dry / wet mergers, the ubiquity of fine structures will go from none to significant. Further indications on the mass assembly are given by the size and color of the outer stellar halo of galaxies. Therefore by studying the outskirts of galaxies, in particular their stellar populations, one can learn about their main formation mechanism. Most efforts in this direction have so far been done for very nearby spiral galaxies; because Early-Type Galaxies (ETGs) are the most powerful probes at low redshift of the hierarchical mass assembly of galaxies, they should exhibit even more fine structures than late type galaxies. I will present our on-going work to characterize the external parts of massive nearby ETGs which relies on: - stunning extremely deep, wide-field, optical images obtained at CFHT of field and cluster ETGs obtained as part of the resp. ATLAS-3D and NGVS projects, which reveal a wealth of unknown faint structures and extended halos at levels as faint as 29 mag/arcsec2. - state of the art numerical simulations of mergers, either idealized or made in cosmological context, which are used to interpret the observational data and constrain the mass assembly of galaxies. Our analysis revealed a correlation between the fine structure index (which parametrizes the amount of tidal perturbation) of the ETGs, their stellar mass, effective radius and gas content. We will discuss the implications of these results on the mass assembly of massive galaxies and the build-up of their scaling relations.
Stellar Populations at High Redshift: Progress and Challenges
I will review the progress being made in the observational study of galaxies at high redshift through HST and Spitzer imaging, deep spectroscopy and resolved studies with laser-assisted guide star adaptive optics. A coherent picture of galaxy assembly is emerging but there are many untested assumptions regarding the nature of stellar populations at early times. I will discuss the prospects for further progress in this area with current and future facilities.
Wide Field Views of Nearby Galaxies
Evidence is mounting for the presence of complex low surface brightness structures in the outer regions of galaxies. While the most spectacular examples are provided by systems hosting coherent debris streams, the most common examples may be extremely diffuse stellar envelopes. Wide-field imagers on large telescopes are allowing us to quantitatively explore the resolved stellar populations in these components within and well beyond the Local Group. I will highlight some recent results from this work and discuss the insight these outer structures provide on understanding massive galaxy assembly.
The evolution of the stellar populations of massive galaxies since z=0.7
The population of massive galaxies is observed to undergo significant evolution in mass and number density since z=1. Detailed studies of the stellar populations of intermediate-redshift galaxies can shed light onto the physical processes responsible for such evolution. We have undertaken such a study by means of deep multi-object rest-frame optical spectroscopy with IMACS/Magellan on a sample of 80 z=0.7 galaxies with masses >10^10 Msun. These spectra allow us to measure the most relevant age- or metallicity-sensitive stellar absorption features which we interpret with a Monte Carlo library of star formation histories to estimate luminosity-weighted mean stellar ages, metallicities and masses by means of a Bayesian approach. This is the first study to perform measurements of spectral features and estimate physical parameters on individual sources for a representative, mass-selected sample of intermediate-redshift galaxies. The so-derived properties of the z=0.7 galaxies are directly compared with those of local galaxies (SDSS) estimated with the same approach and spectral diagnostics. This allows the first characterization of the mass-stellar metallicity and mass-age relations at z=0.7 and to quantify their evolution to z=0 in an unbiased way. We observe a similar increase in stellar age and metallicity with mass as for local galaxies, with a larger scatter below 10^11Msun, suggesting an evolution in redshift of the characteristic transition mass. The most massive (M>10^11Msun) z=0.7 galaxies have low specific star formation rates (<3x10^11 yr^-1). Assuming that they would evolve passively until today, they could make up only the oldest part of the present-day population at these masses. Their metallicity distribution is instead already similar to the local one. Lower-mass z=0.7 galaxies which have higher specific SFR and stellar metallicities already comparable to local galaxies need thus to evolve into the younger end of the present-day massive population without contributing additional scatter to their metallicity distribution.
Searching for the Progenitors of Massive Elliptical Galaxies at z~1.5--2
Galaxies with very low specific star--formation rate, including systems which are essentially passively evolving, have been identified at redshift up to 3. These systems can have stellar mass that compares or even exceed massive elliptical galaxies in the local universe. Some are also observed to be extraordinarily compact, with stellar density ~2 orders of magnitude larger than that of today's ellipticals. While relatively common at z~2, today these compact ellipticals today are extremely rare. How these systems formed, how and why they have shut down their star formation activity, and how they have evolved into their present day's counterparts remains large unconstrained. Here we present the results of our attempt to identify the progenitors of massive ellipticals at z~1.5--2 among star--forming galaxies at z>3 selected in the CANDELS fields. The galaxies are indentified using a variety of selection criteria to be star forming, with rates and stellar masses consitent with them evolving into the z~1.5--2 ellipticals. We use the CANDELS WFC3 images to characterize their rest--frame optical morphology and size.
The early early type: passive stellar populations at z=3
Most of the stellar mass in the local Universe is contained in massive, so-called early-type, galaxies whose old ages imply that they formed at high redshift. The epoch where these stellar systems first appear has been only loosely constrained, however, and their modes of formation not clearly understood. This mostly stems from the relatively low number of early-types discovered so far at z~2 and none at z>3, as they are harder to detect and confirm than blue, star-forming galaxies. Those that have been detected are often found to be structurally different than their low redshift counterparts and the question of their transformation into their present-day descendants is still unsolved. I will present the discovery of the first genuinely passive galaxy confirmed to be at z=3 and discuss the implications of the existence and characteristics of this remarkable object on our understanding of massive galaxy evolution.
The stellar populations in the halo pf NGC 253 as seen by VISTA
As part of the VISTA science verification programme we have obtained Z and J band images of the nearby edge-on spiral galaxy NGC 253. The wide field of view of VISTA allows us to map the halo of the galaxy up to a distance of ~ 40 Kpc from the center. Over most of the field we detect Red Giant Branch stars, which we use to trace the galaxy profile and to determine how far the halo extends. We also detect Asymptotic Giant Branch stars, but virtually no young stellar population outside the disk of the galaxy. We discuss our spatially resolved Colour Magnitude Diagram in terms of star formation and assembly history of the galaxy.
Subaru Wide Field Photometric Survey of Nearby Spiral Galaxy M33
Nearby galaxies are of special importance to the study of stellar populations in a sense that detailed signs of different stellar populations in a galaxy can be resolved, which is crucial for our understanding of the formation and evolution of various types of galaxies. This has been a major motivation behind many wide field photometric surveys of nearby galaxies during the last decade. Here, We present another deep and wide field photometric survey of M33 that is the nearest Scd type spiral galaxy in the Local Group. M33 is also being considered as an interacting companion to another gian spiral galaxy M31, which makes M33 even more interesting target for the detailed stellar population study. We have obtained B,V,R,I multi-band images of M33 by taking advantage of the power of wide field imager SprimeCam mounted on the 8.2m Subaru telescope. The coverage of our imaging survey includes the very outer part of M33, extending out to about 100 acrmin from the galaxy center, as well as the whole disk of M33 spanning about 1 deg x 1 deg area. Our photometry goes down to V~27 mag in the outer part of M33 and V~25 mag in the central part of M33 disk, providing one of the best datasets available for such a wide area around M33. We are going to present the results of star cluster surveys and stellar population studies on M33 empowered by the comprehensive survey with SuprimeCam/Subaru.
Chemical evolution of r-process elements in the framework of hierarchical formation of the Milky Way
Metal-poor stars record formation and enrichment process of our Galaxy at the early epoch. Observed abundances of r-process elements, e.g. Sr, Ba, and Eu, in those stars show large star-to-star scatters, while dispersions in those of lighter elements, such as alpha- and iron-peak elements, are much smaller. On the assumption that the site of r-process is in specific supernovae, it has been discussed that this may come from incomplete mixing of the interstellar medium. However, recent nuclear-astrophysics studies suggest that neutron star mergers can be more plausible site rather than core-collapse supernovae, although controversial results are pointed out by previous chemical evolution studies. In this study, we investigate the role of neutron star mergers in the enrichment history of the r-process elements in the framework of the hierarchical formation of the Milky Way from a large number of sub-halos. We find that neutron star mergers can be a major source of the r-process elements if the smaller sub-halo has the lower star formation rate as indicated from the spectroscopic studies of some dwarf spheroidals. Our result naturally explains both the large star-to-star scatter of the r-process abundances and the small scatter of the alpha and iron-peak abundances as found in extremely metal-poor stars of the Galactic Halo.
How time and space matter in the evolution of cluster galaxies
I will present some new results of the EDisCS project.
Massive early-type galaxies: the last 12 billion years
I review our understanding of the formation of massive early-type galaxies (ETGs), in the context of survey studies that exploit rest-frame UV-optical photometry. Recent work that leverages the rest-frame UV (using GALEX at low z and optical HST surveys at intermediate z) have put unprecedented constraints on ETG evolution since z~1. While the bulk of the stars in ETGs are indeed old, these studies indicate widespread star formation in these systems, that creates ~20% of their stellar mass at z<1, via repeated minor mergers between ETGs and gas-rich dwarfs.
While the late-epoch (z<1) evolution of ETGs has been quantified in detail, surprisingly little is known about exactly when and how the dominant (~80%), old stars in these galaxies formed. This requires a survey-scale (UV-optical) study of newborn ETGs in the early Universe, which is only now becoming possible. Exploiting new HST/WFC3 near-infrared imaging and existing HST/ACS optical imaging in GOODS-South, I present a large empirical study of newborn ETGs around the epoch of peak cosmic star formation (1 Chemodynamical simulations of galaxies TBD MAHALO-Subaru: Mapping Star Formation at the Peak Epoch of Galaxy Formation MAHALO-Subaru (MApping HAlpha and Lines of Oxygen with Subaru) is our on-going large programme which aims to investigate how the star forming activities in galaxies are propagated as a function of time, mass, and environment. We are targeting 13 clusters and proto-clusters at 0.4 < z < 5.2, and two general fields (GOODS-N and SXDF-CANDELS) with Suprime-Cam and MOIRCS by utilizing our unique sets of narrow-band filters. The narrow-band imaging can map out star forming galaxies with the redshifted Halpha and/or [OII] emission lines from our targets, and thus providing unbiased views of star forming activities across time and environment. We have completed Halpha/[OII] imaging of 7 proto-clusters at 1.5 < z < 2.5 at the peak epoch of galaxy formation, and found that star forming activity is indeed very high even in the proto-cluster cores, and that the peak of star formation is shifted outwards with time, indicating the inside-out formation of clusters. Moreover, we have identified many ""red"" emitters especially in high density regions, which suggests that the mode of star formation or the activation of AGN may depend on environment. In this presentation, we will give an overview and a progress report of this project, and some exciting early results. Gas Accretion and Outflows from Intermediate Redshift (z~1) Galaxies Galactic-scale gaseous inflows and outflows play an integral role in shaping the star formation rate, stellar mass, gas nature and content, structure, metallicities, etc. of galaxies. Yet, observations of such gas remain limited for distant galaxies during their more active phases of formation and assembly. We present highlights from a Keck spectroscopic survey of about 100 galaxies at 0.3 < z < 1.4 selected from the GOODS fields and the Extended Groth Strip. Instead of using background QSO's to reveal the galactic and circumgalactic gas of foreground galaxies, we use the light from the galaxy itself to probe the galaxy's gas. Adopting the mean velocity of ionized gas emission as the reference frame, this approach has the tremendous advantage of directly revealing whether the observed gas is moving towards or away from the galaxy, which is otherwise ambiguous for QSO observations. An analysis of UV lines of MgII and FeII predominantly reveals outflows of cool gas via the blueshift of the absorption lines. Sizes from HST imaging suggest only a weak dependence of outflow velocity on SFR and SFR surface density, with outflows occurring in galaxies over the full range in SFR surface density probed. While outflows dominate our sample, cool gas inflows have been discovered toward 6 star-forming galaxies, based on positive velocity shifts for cool gas. HST images tantalizingly show that five of the six galaxies have highly inclined disk-like morphologies. These data are among the first unambiguous detections of inflow into isolated, star-forming galaxies in the distant universe. We suggest that the inflow is due to the infall of enriched material from dwarf satellites and/or a galactic fountain within the galaxies. Red Star Forming Galaxies over 10Gyrs: a Key Population under Environmental Effects? We present our systematic wide-field Halpha emitter survey of distant galaxy clusters at z=0.4, 0.8, and 2.2 using narrow-band filters installed on the Subaru Telescope, as well as obscured activities in these cluster fields based on the mid-infrared data taken with Spitzer and AKARI. Taking advantage of the wide-field of views of Suprime-Cam and MOIRCS, our Halpha survey covers wide range in environment from cluster core to surrounding structures (over ~10Mpc) at all redshifts. The most striking result of this project is that a surprisingly large number of ""optically red galaxies"" are showing strong Halpha emissions in all redshifts, and in fact many of them are MIR-detected dusty starbursts (i.e. they are not just gradually fading their star formation). Interestingly, we find that the environment of such red star forming galaxies are changing through cosmic time: they are most numerous in the proto-cluster core region at z~2, while they are located in the cluster outskirts or surrounding groups at z<1. Our survey also revealed that the environment of the red star forming galaxies coincide with the ""transition environment"" (where we see a sharp break in the colour-density relation) at z<1, suggesting that the red star forming galaxies are triggered by the environment and related to the subsequent environmental quenching of galaxy activities. Thus, our wide-field Halpha + MIR approach towards the distant cluster environments has now provided a new insight on the ""hidden side"" of cluster galaxy formation and evolution over ~10Gyrs. Formation of Giant Elliptical Galaxies and Globular Clusters A pioneering paper by Arimoto and Yoshii (1987, 'Chemical and Photometric Properties of a Galactic Wind Model for Elliptical Galaxies') prompted numerous theoretical and observational studies to investigate how elliptical galaxies formed and evolved.
Around the time when this paper was published, little was known about the nature of globular clusters in elliptical galaxies.
Globular Clusters are an excellent tool for understanding
how giant elliptical galaxies formed.
I present an overview of recent findings on photometric, chemical, and kinematic properties of globular cluster systems in giant elliptical galaxies, and discuss their implication with respect to how giant elliptical galaxies formed and evolved in the local universe. Insights from the simple evolution of the galaxy population I will review and discuss the insights that come from identifying various striking simplicities and uniformities in the global properties and evolution of the galaxy population over cosmic time. I will focus specifically on the surprising constancy of M* and alpha for star-forming galaxies, the form of the sSFR(m,t) relation, and the separability, at least at low redshift, of the effects of mass and environment. I will also highlight the surprising independence of many properties of satellite galaxies on the mass of the parent dark matter halo. Multi-wavelength SED-fit and galaxy evolution with applications TBD Co-evolution of Galaxies and Central Black Holes: Extended Ionized Gas around AGNs A comprehensive analysis of extended emission-line region (EELR) around quasars is presented. EELR is a massive ionized nebula observed in some active galactic nuclei (AGNs).
It extends to several tens of kiloparsec from the central engine, and is clearly photoionized
by the AGN radiation. By combining new Subaru/Suprime-Cam observation with the archival data,
it is found that EELR phenomenon shows clear correlation with Eddington ratio, which links EELR
to the principal component 1 (PC 1), or eigenvector 1, of well-known AGN emission correlations.
We also find that EELR is preferentially associated with gas-rich, massive blue galaxies.
It supports the idea that the primary determinant of EELR creation is the gas availability and
that the gas may be brought in by galaxy merger triggering the current star formation as well
as AGN activity, and also gives an explanation for the fact that most luminous EELR is found
around radio-loud sources with low Eddington ratio. By combining all the observations, it is
suggested that EELR quasars occupy the massive blue corner of the green valley, the AGN realm,
on the galaxy color - stellar mass diagram. Once a galaxy is pushed to this corner, activated
AGN would create EELR by the energy injection into the interstellar gas and eventually blow it
away, leading to star-formation quenching. Our results provide a piece of evidence for the
presence of such AGN feedback process, which may be playing a leading role in the co-evolution
of galaxies and super-massive black holes. The preprint is available at arXiv:1203.1356.
In and around the Local Group I will present recent discoveries and results from the Pan-Andromeda Archaeological Survey relating to the structure and content of the Andromeda sub-group, in particular focussing on the properties of its dwarf satellite galaxies. I will discuss how the comparison of these systems with the Milky Way sub-group is informing our understanding of galaxy evolution at the faintest magnitudes. Finally, I will highlight what are, in my view, some key outstanding questions that the population of nearest galaxies can help to answer. Star Formation Histories and Initial Mass Function of Early-Type Galaxies from Atlas3D The stellar populations of present-day early-type galaxies (ETGs) carry the record of galaxy evolution processes integrated over cosmic time. Using a multi-wavelength approach, the Atlas3D survey reveals these objects to span a broad range of properties, from commonly hosting sites of active star formation, to harbouring the most ancient known populations that trace an epoch of galaxy evolution long since completed. We present the star-formation histories from spectral fitting of our complete sample, and discuss the connections of our findings to the global scaling relations of ETGs. We also compare our findings to recent semi-analytic and numerical models. Thanks to our high-quality spectral maps, we can tightly constrain mass-weighted population parameters as well as general stellar dynamical models. This provides us with a unique opportunity to accurately compare gravitational predictions with those of stellar population models. By constraining the dark-matter contribution, we break the long-standing degeneracy between dark matter and the initial mass function (IMF), allowing us to robustly explore variations of the IMF across our large sample of ETGs. "Stellar populations, morphology and scaling relations on the red sequence in clusters and groups at z>1" We present recent results of stellar populations, morphology and the mass-size relation of galaxies on the red sequences in clusters and groups at z>1. We will concentrate on the Lynx supercluster at z~1.3, and compare galaxy properties to those of galaxies in the field at the same redshift. Testing galaxy formation models with the GHOSTS survey: The stellar halo of M81 The GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disks and
Star clusters) survey is the largest study to date of the resolved
stellar populations in the outskirts of disk galaxies. The sample
currently consists of 16 nearby disk galaxies, whose outer disks and
halos are imaged with the Hubble Space Telescope (HST). Here I will
present new results obtained from the study of 19 fields near M81. The
observed fields probe the stellar halo of M81 out to projected
distances of ~ 50 kpc, an unprecedented distance for halo studies
outside the Local Group. I will compare our results with
cosmologically motivated models and discuss implications on M81's
formation history. The Role of Environment and Self-regulation in Galaxy Evolution at z ~ 1 It is well known that in the local universe the properties of galaxies correlate strongly with both their stellar mass and their environment. As of yet, it is unclear whether environment is as important in the process of galaxy evolution
at z = 1 as it is at z = 0. One major uncertainty arises from the difficulty of quantifying galaxy environment at high redshift. Rich clusters of galaxies are the most extreme environments at all redshifts and hence better constraints on the effects of environment can be ascertained by comparing the properties of cluster galaxies to field galaxies at z = 1. I will present a such a study using new data from the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS). I will show that both stellar mass and environment clearly influence the evolution of the galaxy population at z = 1; however, the way in which they do so is quite different.
Stellar populations of faint dwarf satellites of the Milky Way Dwarf galaxies around the Milky Way provide us a unique opportunity to investigate galaxy formation and evolution through their resolved stars. Most of them are considered to be both dynamically and chemically simple, with the high M/L ratio. The number of Galactic dwarf satellites (dSph) is doubled in recent years thanks to systematic surveys in the SDSS data archive.
We present the deep colour-magnitude diagrams (CMDs) of Galactic dSphs, including recently discovered faint ones. The images taken by Subaru/Suprime-Cam are sensitive enough to derive the stellar ages based on the main sequence turn-off, and wide enough to study the spatial distribution of stars in each galaxy. The resulting CMDs show that the brighter galaxies have relatively younger populations than these of fainter ones. In the brighter dSphs, the younger populations are more spatially concentrated to the galaxy center than old stars, indicating that the star formation in the central region continued at least a few Gyr, consistent with the different spatial distributions of red and blue HB stars. On the other hands, the CMDs of the faintest satellites show a single epoch of star formation as a metal-poor Galactic globular cluster. This result indicates that the gases in the progenitors of UFDs were removed more effectively than those of brighter dSphs at an occurrence of their initial star formation. We also discuss a future opportunity for searching further faint galaxies by Hyper Suprime-Cam. Deep near-infrared spectroscopy of passively evolving galaxies at z>1.4 I will present the results of near-IR spectroscopic observations of passive galaxies at z>1.4 in the COSMOS field. The observations have been conducted with Subaru/MOIRCS and have resulted in absorption lines and/or continuum detection for 16 out of 19 objects down to K=21 (18 of 34 in total). I will highlight the results on the comparison between photometric and spectroscopic redshifts, overdensities of passive galaxies, and stellar populations through absorption features. GOODS-Herschel: dust attenuation in star forming galaxies up to z~4 Over the past decade dust-unbiased tracers of star formation have substantially improved our view of galaxy formation and evolution. Still, even the deepest FIR images are far from sampling the typical star forming galaxy population at z > 1.5, thus for years to come we will have to rely on the most direct, and yet most dust affected, tracer of star formation: the far UV light.
I will discuss how we can use at our best the available FIR information to learn about median properties of dust attenuation at low and high redshifts.
A star-forming galaxy sample up to z~4, drawn from the GOODS North field, with very accurate photometric redshifts, is used to perform a stacking analysis in the deepest FIR images of the sky, the GOODS-Herschel data set.
Our results include a robust confirmation of previous results on more massive star forming galaxies being more dust rich and more attenuated in the UV.
For the first time, this study shows that this correlation, between galaxy stellar mass and UV dust attenuation, remains the same over the last 13 Gyrs of cosmic time. Colours, colour gradients and inverted scaling relations for early-type galaxies from Spitzer [3.6]-[4.5] imaging I discuss the [3.6]-[4.5] Spitzer-IRAC colour behaviour of the early-type galaxies of the SAURON survey of nearby ellipticals and lenticulars. I will demonstrate how this colour, which is unaffected by dust extinction, can be used to constrain the stellar populations in these galaxies. I will show that this colour is an excellent tool to study stellar population gradients in galaxies, and that tight scaling relations are found that can be used to study the relative contribution of AGB stars in these galaxies. At the end of the talk I will discuss the behaviour of galactic bulges in these bands.
We are the 0.3%! Globular clusters as elitist stellar populations. The early build up of stellar populations in nearly all galaxies involved an intense epoch of star formation whose most prominent survivors are today's globular clusters (GCs). On average, only ~0.3% of galactic baryonic mass is in the form of present-day globular clusters, yet their ubiquity and visibility provide us a unique and complementary window onto the early epochs of galaxy building across galaxy mass, morphology, and environment. With the combination of HST and wide-field ground-based facilities, we have been able to study extragalactic GC systems in new detail. I will review our current knowledge of extragalactic GC systems as told by HST studies of nearby galaxy clusters (Virgo, Fornax, Coma), as well as describe new advances from the Next Generation Virgo Survey (NGVS) CFHT Large Programme. I will focus in particular on the metallicity distributions, formation efficiencies, kinematics, and spatial density distributions of GC systems, and what they tell us about the early formation of stellar halos. Mass and metallicity assembly in galaxies: CALIFA's 3D view. We have engaged on a large 3D integral field spectroscopic survey of 600 galaxies in the local universe (CALIFA).
We apply the fossil method of stellar population spectral synthesis to recover the 3D star formation history of each galaxy from its spectra.
Here we present the results from the analysis of the first 150 galaxies observed.
We show that galaxies in the local universe have grown inside-out.
The relative rates of mass growth are larger in the nucleus, than within the effective radius, and in turn larger inside than outside the effective radius.
There is a maximum relative growth for the nucleus in the galaxies located in the green valley with respect to the blue cloud and the red clump.
We also show how galaxies build in time their spatial gradient of metals.
Further, we show how the rate of mass growth depends on the galaxy mass, so that massive galaxies assemble their mass very quickly early on, while lower mass galaxies are still in the process,
and how the rate of build up of the metallicity gradient depends on the parent galaxy mass.
"What we would like to know, what we would like to understand" Quite obviously, we would like to have a better mapping of the galaxy populations through cosmic times. But, more specifically, there are quite a few urgent (and burning) questions that observations can answer. For example, we would like to know what is the slope, width and redshift evolution of the ""main sequence"" of star-forming galaxies; or whether their specific star formation rate is independent of environment at all redshifts. What is the age distribution of stars in the various Milky Way components (halo, bulge and disk)? I will list several other similar questions. Then, while we spend efforts and telescope time trying to answer them, we are urged by another kind of questions, as ultimately we would like to understand what is going in physical terms, i.e., to identify the key physical processes that are driving galaxy evolution. For example: what keeps the ""main sequence"" such through cosmic times? Is star formation quenching an internal or an external process? Does halo mass or stellar mass matters in this respect? How the Galactic bulge was formed? These, and other similar questions will resonate during the meeting. The Galactic Bulge We report results from the Bulge Radial Velocity Assay, and studies of the bulge chemical composition from new observations on the bulge minor axis. The bulge exhibits cylindrical rotation and other characteristics that point toward the formation of a bar via the buckling of a massive disk. However, some properties, like the presence of an abundance gradient, conflict with a purely dynamical process. We consider how future surveys like the Jasmine project may help to resolve a range of observational questions. Evidences of mergers at high redshifts Optical-SPITZER-submm SEDs of extreme high-z radio galaxies (z~4)
are analyzed with the new version of the evolutionary code PEGASE.3
(Fioc, Dwek, Rocca-Volmerange, 2012) .
The code predicts the coherent stellar, gas and dust absorptions/emissions
of various spectral types at all ages.
We find the two stellar (old and young) components derived from predictions are
surprisingly well confirmed by the recent HERSCHEL observations.
(Rocca-Volmerange & part of the HERGE consortium, 2012).
Consequences on galaxy evolution and cosmology are discussed.
UV spectral slope of faint redshift 7 galaxies: measurement biases and variability With near-IR imaging in the Hubble Ultra Deep Field reaching depths of
29th magnitude, the physical properties of the z=7 galaxy population are
now being probed via stellar population model fitting. In lieu of
rest-frame UV continuum spectroscopy, broad-band photometry is commonly
used to measure the UV continuum slope, beta (where
F_lambda ∝ lambda^beta), in an effort to constrain the age, metallicity
and dust content of z=7 stellar populations. Initial claims that the
faintest of these galaxies exhibit extremely blue rest-frame UV slopes
(beta=-3), implying exotic (ultra low metallicity, very young) stellar
populations at the epoch of reionization, have since been refuted on the
basis of observational biases. For example, traditional colour-colour
selection techniques are most robust for high-redshift galaxies with the
bluest UV slopes and flux boosting of faint objects to just above the
detection threshold can skew the mean population colours. At present,
various methods are employed to measure the UV slope: using a single- or
multi-colour power law fit or a pseudo-spectroscopic measurement via the
best fit population synthesis model. We have performed detailed
object-recovery simulations of the HUDF and ERS fields and identified the
biases associated with each method. Using both existing data and
simulations of deeper WFC3/IR imaging of the HUDF scheduled for August
2012 (UDF-12), we will present an optimal method for measuring the
rest-frame UV slopes of z=7 galaxies and discuss how best to utilise
population synthesis models to this end. Planetary Nebulae in the Optical Regions of Early-type Galaxies: the SAURON view Planetary Nebulae (PNe) in external galaxies are mostly regarded either as tracers of the gravitational potential or as indicators for the distance of their galactic hosts, with the latter advantage owing to the almost universal -- though not fully understood -- shape of the PNe luminosity function (PNLF, generally in the [OIII]5007 emission).
Yet extra-galactic PNe can also be used as probes of their parent stellar population, and understanding in particular the origin of the PNLF is a puzzle that, once solved, promises to reveal new clues on the late stages of stellar evolution and therefore also a better picture on the origin of the integrated UV-fluxes from old galaxies.
In this talk, will show how integral-field spectroscopy allows to detect PNe in the optical regions of galaxies to flux levels otherwise inaccessible to standard narrow-band photometry. This allows to trace the PNLF in the same galactic regions where the properties of stellar populations can be well characterised, thus making it possible to relate the shape of the PNLF to the PNe parent population.
More specifically I will present a) results based on the detailed analysis of SAURON data for M32 and M31, showing for the first time that the PNLF is in fact not universal, b) a preliminary analysis for more distant galaxies from the SAURON survey and c) conclude by showing the future prospect of this field with next generation integral-field units such as MUSE on VLT. The build-up of mass in sub-L* galaxies at high redshift We probe deep (R_lim=28) into the UV-selected z~2 galaxy population to study how galaxies build up their masses. We find that the low-mass end of the stellar mass function is steeper than extrapolations of brighter surveys would suggest, and this implies that the universe has converted more mass into stars by this epoch than was previously thought. We also find that sub-L* galaxies at z~2 carry very small amounts of dust compared to their more luminous cousins, so that while only ~20% of UV photons escape from a typical M* galaxy, more than half make it out of an M*+3 one; this paucity of dust means that sub-L* galaxies are important contributors to keeping the Universe ionized at z~2. Turning to clustering measurements, we find that the star formation rates in the most massive haloes decline with redshift, so that while ~1e12 M_sun halos at z~3 and 4 are host to >50 M_sun/yr of star formation, at z~2 they produce ~20 M_sun/yr, and at z~1.7 only ~2 M_sun/yr. We interpret this as shut-down of star formation in the most massive halos and evidence that galaxy downsizing is related not just to galaxy stellar masses, but to the masses of the dark matter halos that host them.
New insight on stellar populations and star-formation histories of Lyman break galaxies Using our state-of-the-art SED fitting tool allowing for the effects
of nebular emission and utilizing extensive Monte Carlo simulations,
we have carried out a detailed analysis of the physical properties and
their uncertainties for a large sample of Lyman-break Galaxies from
redshift z~3 to 6 and beyond.
We consider a large variety of star-formation histories, variable
extinction, models with and without nebular emission, and variable
strengths of Lyman-alpha emission. We derive the main physical parameter
such as stellar mass, SFR, extinction, and discuss critically their
uncertainties and dependence on model assumptions.
Our results provide in particular new insight into the evolution
of dust and the specific star-formation rate with redshift, on the
typical timescales of star-formation, and on related issues. We also
show how ALMA observations and near-IR spectroscopy can provide
definite tests for different star-formation histories evoked in the
literature.
Constraining the Evolution of massive galaxies via halo occupation and semi-analytic models One of the still mostly debated topics in Cosmology is the formation and evolution of massive, spheroidal galaxies, for which galaxy evolution models sometimes offer disparate explanations. In my talk I will present results from a new code that evolves massive galaxies via a hybrid approach. The basic idea of our modelling is to follow the hierarchical merger histories of haloes, and at each timestep during the evolution, “paint” galaxies onto haloes via Halo Occupation Distribution (HOD) techniques. The latter rely on tuning the median monotonic (sub)halo mass-stellar mass relation (including its scatter) that fully satisfies the constraints of stellar mass function and galaxy clustering properties at all redshifts. A galaxy inside the main progenitor branch of a tree is then at each time-step initialized until a merger occurs, then all its structural and photometric properties are updated following recipes inspired by the results of numerical simulations of several galaxy mergers. HOD models have the virtue that they do not require full ab initio physical recipes to grow galaxies in dark matter haloes, as in full semi-analytic models. This in turn allows to by-pass the still substantial unknowns about, e.g., star formation and feedback in galaxy evolution models. By comparing with a variety of new statistical, structural, photometric, and clustering data sets, such as the size-stellar and color-mass relations, I will show how we can successfully break degeneracies in the models and constrain galaxy evolution models. In particular, during my talk I will discuss the hot topic of the size evolution of early type galaxies, the role of environment versus mergers, the origin of the highly non-linear color-mass relation recently inferred in SDSS, and conclude with a brief digression on galaxy clustering, all topics of extremely relevance for the large and deep ongoing and future surveys such as BOSS and EUCLID. Feedback in Galaxy Formation TBD Tracing the distribution of star-forming galaxies at z~1.5 in COSMOS with Subaru/FMOS We present preliminary results from a new spectroscopic survey of star-forming galaxies in COSMOS with FMOS, a multi-aperture, near-infrared spectrograph on the Subaru Telescope. Our survey is designed to detect Halpha in emission for star-forming galaxies at 1.2 < z < 1.7, a regime particularly challenging for current optical spectroscopic surveys. We will discuss the properties of galaxies on the main sequence of star formation and those that lie above such a relation with particular attention to the Herschel/PACS sources. In addition, we will address the primary focus of our program to map the large-scale distribution of galaxies and determine whether the environment plays a role in galaxy evolution (including black hole growth) at high redshift.
Stellar populations on the red sequence: the view from Coma (and z=0.3) I will summarize my recent results derived from age and metallicity estimates for giant and dwarf galaxies in the Coma cluster, as well as from new deep observations of clusters at z=0.3. I will show how the star-formation history in now-passive galaxies varies as function of mass and environment. The ages of red-sequence giants are primarily determined by galaxy mass, with only weak modulation by environment, in the sense that galaxies at larger cluster-centric distance are slightly younger. For red-sequence dwarfs, the roles of mass and environment as predictors of age are reversed: there is little dependence on mass, but strong trends with projected cluster-centric radius are observed. I show how these results can be interpreted using environmental histories extracted from the Millennium Simulation for members of massive clusters. Hierarchical cluster assembly naturally leads to trends in the accretion times of galaxies as a function of projected cluster-centric radius. If galaxies are quenched when they become satellites, or on infall into halos above some threshold mass, such trends can account for the observed correlations. For the dwarf galaxies, the efficiency of environmental quenching must be close to maximal. Ongoing work is extending these comparisons to clusters observed at intermediate redshifts using very deep observations with VLT. Preliminary results from this project are already in hand for ~100 galaxies in two clusters, and I will present the first analysis of this sample at the meeting. The 11 Gyr Evolution of Star-forming galaxies I will present new results from deep and wide narrow-band surveys undertaken with UKIRT, Subaru and the VLT; a unique combined effort which has resulted in large, robust samples of H-alpha (Ha) emitters at z=0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyrs) in a uniform manner over ~2 sqdeg in the COSMOS and UDS fields. The deep Ha surveys are sensitive to Milky-Way SFRs out to z=2.2 for the first time, while the wide area and the coverage over two independent fields allows to greatly overcome cosmic variance. Both the shape and normalisation of the Ha star formation history that we derive are consistent with the measurements of the stellar mass density growth, confirming that our Ha analysis traces the bulk of the formation of stars in the Universe up to z~2.2. Our large and homogeneously selected samples of Ha emitters at different epochs also provide us with a unique view on the evolution of star-forming galaxies and what has been driving it for the past 11 Gyrs. The stellar IMF of early-type galaxies. Constraints from strong lensing The stellar initial mass function (IMF) is a fundamental parameter for the characterization of stellar populations.
Is the IMF universal?
To answer this question it is necessary to determine the IMF in a range of different environments, but directly measuring the mass distribution of stars outside the Milky Way is very difficult.
In red early-type galaxies, the IMF is the parameter to which mass-to-light ratio measurements from stellar population synthesis models are most sensitive to.
In cases where independent measurements of the mass-to-light ratio are available, the IMF can be observationally determined.
Strong gravitational lensing and stellar dynamics provide accurate measurements of the mass-to-light ratio of bulges of massive galaxies, independently from assumptions on their stellar population.
By comparing these measurements with stellar population synthesis models we can then discriminate between a Chabrier and a Salpeter IMF for these objects.
I will present a high precision measurement of the IMF of a massive early-type galaxy and trends of the IMF with galaxy mass and age from lensing surveys. Quiescent early-type galaxies in groups and clusters at z>1.5 We present recent results from our on-going work on z>1.5 galaxy
groups and clusters. We are conducting an X-ray search of distant
clusters in deep fields and we have identified a few z>1.5 systems
so far. We briefly summarize our discoverties and then focus on
a newly discovered system at z=1.61. Its mass inferred from X-rays
is only 3x10^13 Msun, making it the lowest mass group ever
confirmed at z>1.5. The group is likely a progenitor of a present-day
cluster of a typical mass. Based on the deep HST/WFC3 data from
CANDELS, we find that the group galaxies form a surprisingly
prominent red sequence. Detailed SED fits based on deep
multi-wavelength photometry show that most of the group members
are indeed quiescent galaxies. Furthermore, their morphological
parameters derived from the WFC3 data show that they are early-type
galaxies. The group thus appears strikingly similar to those
in the local universe. The only difference is its high AGN
fraction (~40%), which might indicate a role of AGNs for quenching.
At z>2, there are a number of known 'proto-clusters'. In parallel
to the X-ray survey, we are conducting deep near-IR spectroscopy
of proto-clusters and we present our recent observation of PKS1138
at z=2.16. The PKS1138 proto-cluster hosts a large number of
star forming galaxies, but we spectroscopically confirm for the first
time that quiescent galaxies populate in the proto-cluster environment.
Our results on the z=1.6 and z=2.2 systems might suggest that
the environmental dependence of galaxy properties observed today
is imprinted at high redshifts, possibly during the first gravitational
collapse of clusters. Environment and self-regulation in galaxy formation The environment is known to affect the formation and evolution of galaxies considerably best visible through the well-known morphology-density relationship. Yet, the prevalence of environmental versus self-regulating processes in the formation and evolution of galaxies are still controversially discussed. I present new results on these issues from our recent studies of environment, star formation histories, and AGN activities of early-type galaxies from the large spectroscopic galaxy surveys SDSS, GAMA, and SDSS-III/BOSS. Our key finding is that the stellar population scaling relations of early-type galaxies, describing the correlations of ages and element abundances with galaxy mass, are not sensitive to environmental densities and are only driven by galaxy mass. The DART surveys I will talk about how the study of the photometry, kinematics and chemical abundances of individual stars in nearby dwarf galaxies allows us to access the historical record of galaxy formation and evolution back to the earliest times from the comfort of the nearby Universe. I will primarily talk about the results coming from DART project over the last few years.
The SFRD & Dust Attenuation over 12Gyr The VVDS Deep and Ultra-Deep surveys have mapped ~11,000 galaxies out to z~5. I will present the star formation rate densities and the amount of ultraviolet dust attenuation derived over a 12Gyr cosmic time baseline. Our results yield
an homogeneous view derived from a single survey, using the same methodology rather than a compilation of various datasets at different redshifts. They also unveil the importance of the survivance of dust on long-time scales. Expanding MILES stellar population synthesis models I will present our ongoing efforts at expanding our stellar population
synthesis models based on the MILES stellar spectral library. This include the
extension of the spectral coverage of the models with the aid of other
empirical stellar libraries, as well as predicting alpha-enhanced SEDs at
moderately high resolution, with the aid of both theoretical atmospheres and
expanding the MILES database. These SEDs provide significant
improvements at matching observed spectra, absorption line-strengths and
colours of massive early-type galaxies. These new predictions for simple
and complex stellar populations will be available through a web-based facility.
Following the growth of galaxy groups since z=1 Since many (if not most) low-redshift galaxies are found in groups, finding and characterizing these systems -- and their growth over cosmic time -- is critical to understanding the evolution of their resident galaxies. However, due to the sparse nature of low-mass groups, large volumes and highly-complete spectroscopy are necessary to detect significant numbers. We are now carrying out a novel multi-object prism survey of IR-selected galaxies from z=0.4-1.5, ultimately covering 15 square degrees and an unbiased volume comparable to SDSS. The prism spectroscopy provides accurate redshifts, line fluxes, and continuum measurements, while our Spitzer-IRAC selection ensures that the ""red and dead"" galaxies which populate groups and clusters are not missed by the survey. Here I will present results from the early survey data, including the first measurement of the group stellar mass function since z=1 and the star-forming properties of galaxies in groups vs. the field. A resolved view on stellar populations at cosmic noon I will discuss the relation between structure and stellar populations
among and within galaxies out to z ~ 2.5. These new results on the
emergence of the Hubble sequence are based on high-resolution imaging
with WFC3 and ACS onboard HST. First, I will describe how the global
structure of galaxies depends on their position in the SFR versus Mass
diagram. Next, I will demonstrate how studies of resolved colors and
resolved stellar populations can shed light on the growth and
evolution of early star-forming galaxies (SFGs), and on the nature and
fate of star-forming clumps seen in them. I will present evidence for
color, age, and dust gradients within distant SFGs, such that their
reconstructed stellar mass profiles tend to be more compact and
smoother than the light distribution. Off-center clumps in the light
profiles exhibit bluer colors and younger stellar populations than the
underlying disk, implying a rapid disruption of clumps by efficient
feedback from star formation and/or fast inward migration due to
dynamical friction in gas-rich, gravitationally unstable disks. Nature of a Protocluster at z=3; putting all the pictures together We present the results of a comprehensive observations of the SSA22 z=3.1 protoclusters using Suprime Cam/MOIRCS. Ly Alpha narrow-band bservations covering in total of 2 squre degree peovides the very solid identififcation of the protocluster and the surrounding large-scale structure at z=3.09. We then analyzed deep JHK MOIRCS images to study the distribution of the stellar-mass selected galaxies around the LyAlpha protoclusters. We found significant excess of massive galaxies, color-selected Distant Red galaxies, and dusty 24um-selected galaxies and all these are significantly clustered at around the very peak of the LyAlpha emitters. Color analysis shows that the large fraction of the massive galaxies with more than 10^10.5 Msun in stellar mass are very active star-forming galaxies with substential dust obscuration. On the other hand we also identified rather quiescent passively-evolving population there. Hierarchicall merging events in giant LyAlpha Blobs are also observed.Thus we are witnessing the formation of massive galaxies in heart of the z=3.1 protocluster. Based on these observational results, we discuss the nature of the protocluster. Merger relics in cluster environments van Dokkum (2005) found that the majority of early-type galaxies in the field environment show disturbed morphology. Much of it is attributed to recent dry mergers and naturally led to a conclusion that mergers played a pivotal role to the growth of elliptical galaxies at least in the FIELD environment. Galaxy clusters are generally considered as hostile sites to galaxy mergers due to high peculiar speeds. To test this simple-minded theoretical expectation, we have performed extra-deep (mu=28) optical (ugr) imaging on four DENSE CLUSTERS at z<0.1 using the CTIO/Blanco 4m telescope. To our total surprise, we found that the early-type galaxies in clusters show comparable post-merger galaxy fractions to the field. We compare this observation to our Nbody-backbone-based semi-analytic models and conclude that the post-merger galaxies are exhibiting merger features carried over from the time before they fell into the present clusters. We call this ""merger relics"". According to this interpretation, galaxies in dense environments are indeed less likely to experience mergers in situ due to high peculiar motion, but in reality clusters exhibit much more post-merger galaxies than expected from stationary-halo assumptions because (1) cluster halo mergers are frequent in the hierarchical universe and (2) complete galaxy mergers take long time. Given that mergers have significant impact on star formation and galaxy morphology, we argue that galaxy evolution can be properly studied only when their environments BOTH IN THE PRESENT AND PAST TIMES are accurately assumed/understood in advance.
Stellar populations of moderately luminous AGNs at intermediate redshifts
We will be presenting the first results of a program aimed to study the stellar populations of moderately luminous X-ray selected Active Galactic Nuclei (AGN) at intermediate redshifts. We use observations taken as part of the Survey for High-z Absorption Red and Dead Sources (SHARDS) with the optical instrument OSIRIS on the 10m Gran Telescopio Canarias (GTC). SHARDS is an on-going ESO/GTC Large Programme to observe the GOODS-North cosmological field with 25 medium-band filters (170A) in the spectral range 5000-9500A. Although SHARDS was originally designed to select and study the properties of high-z massive and passively evolving galaxies, it can also provide very valuable information about AGN at intermediate redshifts. We will show that the SHARDS observations provide sufficiently high spectral resolution (R~50) to detect broad absorption stellar features (e.g., the UV Mg feature, the 4000_ break, the CaII absorption features, Balmer absorption series) and emission lines as well as to estimate accurate photometric redshifts of AGN. Together with the SHARDS observations we use the wealth of multi-wavelength data from the UV to radio available for this cosmological field to study the stellar populations and star formation histories of AGN at z~0.5-1.5.
A deep, wide-field study of Holmberg II with Subaru/Suprime-Cam
We present a wide-field optical study of the M81 group dwarf galaxy Holmberg II based on deep Subaru/Suprime-Cam imaging, and analyse the properties of its stellar populations in the context of the comet-like shape of the HI cloud in which it is embedded. Individual stars are resolved down to I~25.2, i.e., about 1.5 mag below the tip of the red giant branch, allowing us to compare the spatial distribution of the young, intermediate age, and old stellar populations. We combine the information from the stellar and gas components to make a case for the presence of a hot intragroup medium in the vicinity of HoII to explain its striking HI appearance.
On the Origin of the Stellar Substructure(s) in Virgo
We present mean three-dimensional kinematics of stars selected from a small pencil-beam region to have properties consistent with membership in the Milky Way stellar substructure in Virgo. The orbit based on our measured kinematics suggests that the Virgo progenitor was on an eccentric (e~0.8) orbit that recently passed near the Galactic center (pericentric distance ~6 kpc). This destructive orbit is consistent with the idea that the substructure(s) in Virgo originated in the tidal disruption of a Milky Way satellite. Simple N-body simulations suggest that the entire cloud-like Virgo substructure (encompassing the ``Virgo Overdensity'' and the ``Virgo Stellar Stream'') is likely the tidal debris remnant from a recently-disrupted massive (~10^9 M_sun) dwarf galaxy. The model also suggests that some other known stellar overdensities in the Milky Way halo (e.g., the Pisces Overdensity and debris near NGC 2419 and SEGUE 1) could be explained by the disruption of the Virgo progenitor. If further chemodynamical exploration of the Virgo structure and the possibly-associated overdensities verifies these results, we will have confirmation of a second (along with the Sagittarius dwarf) recent accretion event of a massive dwarf galaxy into the Milky Way.
Probing kinematical substructures in the Milky Way halo
Phase-space distributions of ancient Galactic stars provide us with basic information on past assembly history of sub-galactic stellar systems. Here we present an analysis of possible kinematical substructures in the Solar neighborhood as revealed in the large samples of the Milky Way stars. Possible association of these substructures with known stellar systems, such as Sgr dwarf and omega Cen, is suggested. We further show our ongoing projects using next-generation wide-field imager and multi-object spectrograph for Subaru to sharpen our perspective on studies of assembly history of the Milky Way as well as Andromeda galaxy.
The Impact of Horizontal Branch Stars on the Evolutionary Population Synthesis Model
We present the Yonsei Evolutionary Population Synthesis (YEPS) model for spectro-photometric evolution of stellar populations. The YEPS model provides various broadband colors, as well as absorption line indices of simple stellar populations (SSPs) with various metallicities, ages, and alpha-element mixtures. Special care has been taken to incorporate the systematic variation of horizontal branch (HB) morphology as functions of stellar parameters. The YEPS model shows that the HB effect does not depend on the specific choice of stellar libraries or alpha-element enhancements. The HBs affect significantly the temperature-sensitive colors and absorption indices. The effect of hot HBs on Balmer lines, usually used for age dating, results in up to a 5 Gyr difference in age estimation of SSPs compared to models without the effect. The YEPS model further reveals that the HBs exert an appreciable effect not only on the Balmer lines but also on the metallicity-sensitive lines, such as magnesium and iron lines. Hence, the HB effect is critical to understanding otherwise-inexplicable phenomena associated with globular cluster systems in our Galaxy and external galaxies, including bimodal index distributions of globular clusters in massive galaxies.
The Star Formation & Chemical Evolution Timescales of Two Nearby Dwarf Spheroidal Galaxies
I will present the detailed Star Formation History of the nearby Sculptor and Fornax dwarf spheroidal galaxies, from wide-field photometry of resolved stars, going down to the oldest Main Sequence Turn-Off. The accurately flux calibrated, wide-field Colour-Magnitude Diagrams are used directly in combination with spectroscopic metallicities of individual RGB stars to constrain the ages of different stellar populations, and derive the Star Formation History with particular accuracy. The detailed Star Formation History shows the star formation at different ages and metallicities, at different positions in the galaxy, and shows that the known metallicity gradients are well matched to an age gradient. The obtained SFH is used to determine accurate age estimates for individual RGB stars, for which spectroscopic abundances (alpha-elements, r- and s-process elements) are known. In this way, I obtain the accurate age-metallicity relation of each galaxy, as well as the temporal evolution of alpha-element abundances. This allows me to study, for the first time, the timescale of chemical evolution in these two dwarf galaxies, and determine an accurate age of the knee in the alpha-element distribution of Sculptor. Finally, I compare the timescale of chemical evolution in both dwarf galaxies, and determine whether the chemical abundance patterns seen in galaxies with recent episodes of star formation are a direct continuation of those with only old populations.
Size evolution in high redshift clusters
We study the effect of environment in the size growth of massive (log(M)>10) red sequence early-type galaxies (ETGs) between z=0.8 and z=1.5. We analyze the mass-size relation of 468 massive ETGs in 9 rich clusters from the HAWK-I cluster survey (hcs.obspm.fr). For all clusters we have deep HST rest-frame B-band imaging to compute sizes together with 4 bands photometry (including VLT/NIR) to estimate stellar masses through SED fitting. Our sample contains the richest and most distant clusters known up to date and it is therefore the best sample available to study the mass assembly of ETGs leaving in extreme environments. Results are then compared to a field population at the same redshifts. Between z=1.5 and z=0.8, we find that the sizes of cluster ETGs are approximately increased by a factor of ~2. However, at these redshifts, the effect of environment seems to have a weaker effect in the size evolution than internal properties of the galaxies such as morphology and stellar mass.
The total versus the sum of the parts: Empirical results
Mega spectroscopic surveys of galaxies near and far are main actors behind the progress seen in the past decade in our knowledge of galaxy formation and evolution. Among many others, the STARLIGHT team has employed full spectral fitting techniques to explore this data-rich epoch to study a variety of issues related to both stellar en gaseous properties. This proved to be a powerful approach, able to produce time-resolved star formation and chemical enrichment histories. Since all results obtained are based on integrated spectra, it is important to evaluate to which extent the analysis of the total is really equivalent to the sum of the parts. The CALIFA survey offers an unique opportunity to address this issue. We have fitted all spaxels of all observed galaxies to obtain 2D maps of properties previously derived only for galaxies as a whole. The richness of this database is impressive. This contribution presents some illustrative results of our STARLIGHT-3D analysis, concentrating on the integrated versus spatially resolved issue. We compare stellar masses, mean ages and metallicities, stellar extinctions and star-formation histories of the spatially resolved and integrated properties. In general terms, the total equals the sum of the parts only when galaxies are uniform in stellar populations and dust, an ideal situation which, as shown by our analysis, almost never happens in practice. The results serve both as a guide to aperture effects in the analysis of large scale datasets and as a precursor of future IFS surveys.
Detailed stellar population analysis of local massive compact galaxies
A tiny fraction of compact massive galaxies was recently found in the Local Universe. Unlike their higher redshift counterparts these objects can be studied with great detail, allowing us to perform a proper characterization and understand better their formation mechanism. I will present a complete stellar population analysis deriving ages, metalicities, abundance ratios, gradients and SFHs as well as other properties such as their kinematics and morphology. Unlike the expectations, these objects show unprecedented large fractions of young stellar components and their abundance ratio pattern differs from that Moreover, these nearby galaxies are almost perfect counterparts in terms of mass, size, shape and age of the compact massive galaxies at z=2.
Pégase.3: A galaxy evolution model of the UV-to-FIR spectrum of dust and stars
Stellar Halo Formation in a Hierarchical Universe: Lessons from Andromeda
Stellar halos provide low density environments where the detritus of hierarchical structure formation can remain visible for billions of years in the form of tidal debris features. In fact, simulations imply that galactic stellar halos are likely composed primarily of tidal debris from past accretion events, providing a record of the galaxy's merger history. I will review what we have learned about the properties of M31's extended stellar halo and M31's merger history from the SPLASH stellar spectroscopic survey, and will compare our observations of the structure and substructure of M31's stellar halo with predictions from simulations of stellar halo formation.
Growth of quiescent galaxies in X-ray selected groups from the COSMOS field
We study how the growth of passive galaxies from z~1 depends on morphology, stellar mass and large scale environment in a uniform sample of field and group galaxies from the COSMOS field.
We find that size evolution strongly depends on the selection. Massive ellipticals (log(M/Msol)>11) doubled their size from z~1, however lower mass ellipticals (10.5 Stellar Mass Growth of Galaxies since z~3 in MOIRCS Deep Survey We present results on the evolution of galaxy stellar mass at 1<~z<~3 from MOIRCS Deep Survey, which is a deep NIR imaging survey with Subaru/MOIRCS in the GOODS-North region. The data reach 5$\sigma$ limiting magnitudes of $J=24.2$, $H=23.1$, and $Ks=23.1$ (Vega magnitude, 2xPSF FWHM diameter aperture) over 103 arcmin$^2$ and $J=25.1$, $H=23.7$, and $Ks=24.1$ in 28 arcmin$^2$ of the survey area. We used the deep NIR data to construct a nearly stellar-mass limited sample down to $\sim 10^{9.5}$--$10^{10} M_{\odot}$ even at z~3. We found that the low-mass slope of the galaxy stellar mass function becomes steeper with redshift and the number density evolution of ~M* galaxies at z>1 is stronger than that of low-mass galaxies. Then we investigated the stellar mass function for quiescent and star-forming galaxies separately. We found that the low-mass slope of the SMF for quiescent galaxies is significantly flatter than that of star-forming galaxies at $0.5 Deep spectroscopy of high-redshift star-forming galaxies in COSMOS In this talk, I will summarize our intensive spectroscopic followup campaign with the Keck/DEIMOS spectrograph for high-redshift galaxies in the COSMOS field. A total of 25 clear nights have been used to obtain deep (3-4hr exposure time per mask), medium resolution (R=2600), rest frame UV spectra of 417 galaxies at z>3. The majority of bright galaxies (z' < 25 AB) in our sample exhibit prominent P Cygni stellar wind lines of CIV and SiIV, suggesting the ubiquity of Galactic outflow among massive star forming galaxies at high redshift. The composite spectrum of ~200 galaxies at Subaru Wide-Field Imaging Survey of the Local Universe: Recent Results and Future Prospect Subaru Telescope is unique among 8-10m telescopes
as it provides wide-field imaging capability by
the prime focus CCD camera (Suprime-Cam).
The local universe is a suitable target for Suprime-Cam
and we are able to explore in extreme deep.
In this presentation, I will summarize the recent results of
our Halpha imaging survey for the Coma cluster.
Our survey revealed the diffuse features traced by Halpha:
a dozen of extended Halpha emitting regions which are thought to be
stripped by ram pressure of dense intra-cluster medium.
We also find that the Halpha luminosity function of the
cluster galaxies shows a steep rise at the faint-end,
indicating that small star-forming activities occur commonly
even at the dense cluster environment in the local universe.
Hyper Suprime-Cam (HSC) is the next generation wide-field CCD camera
for the prime focus of the Subaru Telescope.
It covers the field of view of 1.5 degree in diameter,
which is three times as wide as Suprime-Cam,
by 116 2kX4k fully-depleted CCDs and will be the
ultimate weapon for the Subaru Telescope.
HSC CCD Camera is now on its way to Hawaii following Arimoto-san
and will open its eye in late May.
As Arimoto-san's `first baby' (probably daughter) in Hawaii,
she will provide wealth of findings in various fields
of astronomy and cosmology.
The latter half of this presentation summarizes
the first light performance of HSC and
the science cases for the near-field astronomy
in which I am most interested.
ULIRGs at Redshift z~2 Using the Infrared Spectrograph (IRS) on board the Spitzer, we present IRS spectra of a sample of 14 ultra-luminous infrared galaxies (ULIRGs) in the Extended Groth Strip (EGS) region. The spectroscopic redshifts of this sample are in a very narrow range around z~1.95+-0.1 9, and their IRS spectra have very strong polycyclic aromatic hydrocarbon (PAH) features at 7.7, 8.6, and 11.3 microns. The redshift distribution in our sample is very similar to that of the starburst (SB)-dominated ULIRGs (z~2) studied in other literatures. We estimate the ranges of stellar mass ($M_*$) and star formation rate (SFR) of these z~2 ULIRGs correspond to $M_* > 10^{11}~Msun$ and $410~M_odot$ yr$^{-1}<$ SFR $<1022$ $M_odot$ yr$^{-1}$, respectively. The optical HST/ACS imaging of this sample shows irregular and clumpy morphologies, and a few objects in the sample are so red that they are barely detected at F814W. 4 objects are detected in the HST/WFC3 F160W imaging. Their rest-frame optical morphologies are very diversified including string-like, extended/diffused, and even early type spiral morphologies, implying that there are different formation process for these galaxies. We also search for active galactic nucleus (AGN) signature in our sample using X-ray, radio, and mid-infrared (MIR) emission. About $25-30%$ of the sample show signatures of AGNs in X-ray, MIR or radio. How Do Star-Forming Galaxies at z>z Assemble Their Masses? We investigate how star-forming galaxies typically assemble their masses at high redshift. Using the deep multi-wavelength coverage of the GOODS dataset, we measure stellar mass of a large sample of star-forming galaxies at z~4 and 5, and make a robust determination of stellar mass function (SMF). We report a broad correlation between stellar mass and UV luminosity, such that more UV-luminous galaxies are, on average, more massive. However, the correlation has a substantial intrinsic scatter evidenced by a non-negligible number of UV-faint but massive galaxies. Furthermore, the low-mass end of the SMF does not rise as steeply as the UV luminosity function (alpha_UVLF} -(1.7-1.8), alpha_SMF -(1.3-1.4)) of the same galaxies. In a smooth formation scenario where star formation (SF) is sustained at the observed rates for a long time, these galaxies would have accumulated more mass (by a factor of ~3) than observed and therefore the SMF would mirror more closely that of the UVLF. The relatively shallow slope of the SMF is due to the fact that many of the UV-selected galaxies are not massive enough, and therefore are too faint in their rest-frame optical bands, to be detected in the current observations. Our results favor a episodic formation history in which SF in low-mass galaxies vary significantly over time, a scenario favored by galaxy clustering. Our findings for the UV-faint galaxies are in contrast with those found for more UV-luminous galaxies, which exhibit tighter SFR-M_star correlations. The discrepancy may suggest that galaxies at different luminosities may have different evolutionary paths. The role of galaxy mergers in the evolution of massive galaxies We investigate the role of galaxy mergers in the galaxy mass assembly history using semi-analytic models. In the hierarchical Universe, stellar mass of a galaxy increases via quiescent star formation and dry/wet mergers. Especially, it is likely that massive galaxies in the local Universe more massive than 10^{11} M_ acquire most of their mass through dry mergers for the last few billion years. In this study, we find that specific accreted stellar mass rate of massive galaxies via galaxy mergers is almost constant(~10^{-10}yr^{-1}) during the whole redshift range while SSFR sharply decreases with decreasing redshift. The specific accreted stellar mass rate also stays roughly constant with various parameters that regulate the star formation history. This study also shows that most of the stellar components in massive galaxies did not form in situ but was assembled via minor or major mergers. We also find that the number density of the most massive galaxies (log M/M_=11.0-11.5) grows 2-3 times faster than that of the next massive galaxy group (log M/M_=11.5-12.0) during 0 < z < 1. Although the result seems to contradict the generally accepted concept of cosmological downsizing, it would be a natural result in the hierarchical Universe. The result appears to be consistent with the recent empirical data presented by Matsuoka & Kawara (2010). The puzzling chemical evolution of the Carina dwarf Spheroidal galaxy. CMD analysis have shown for a long time that the Carina dwarf spheroidal galaxy had an unusually episodic star formation history, with active episodes of star formation separated by long periods of no star formation at all.
We will present our new abundances measurements based on VLT/FLAMES spectra. They allow us to examine how the peculiar star formation history of the Carina dwarf spheroidal is reflected in the abundances of several elements and what they tell us on the chemical evolution of this galaxy. Stellar population evolution in cluster galaxies from the Next Generation Virgo Cluster Survey We present recent results on the stellar evolution in cluster galaxies from z~1 to present from the Next Generation Virgo Cluster Survey. Our survey covers 104 sq. deg. centered on the Virgo cluster with deep CFHT/Megacam imaging in five band passes. We detect background clusters with dedicated methods based on the search of red galaxy and photometric redshift overdensities. We analyse galaxy stellar population evolution in clusters from z~1 to present using scaling relations, such as the color-magnitude relation.
The complex physics of dusty star-forming galaxies at high redshifts revealed by HERSCHEL We report on a detailed spectro-photometric investigation of a sample of 31 Luminous and Ultraluminous Infrared Galaxies at z ~1 and 2 selected in GOODS-S. The analysis has been performed by combining data from Herschel surveys (the PACS Evolutionary Probe (PEP) and the Herschel Multi-tiered Extragalactic Survey (HERMES) ), together with deep IRS spectra from Spitzer, and a self-consistent physical model (GRASIL), able to predict the SEDs of galaxies from far-UV to the mm including a state-of the art treatment of dust extinction and reprocessing.
This combination not only allows us precise estimates of the main physical parameters, like stellar mass, star-formation rate, and extinction, but also appears to effectively constrain the galaxy star formation histories (SFH). Assuming the current stellar isochrone library implemented in GRASIL including also the effects of dusty envelopes around AGB stars, we find, on average, for these high-z sources higher extinctions (median Av are 1.56 and 2.45 for z~1 and z~2 (U)LIRG respectively) and stellar masses (median M*=1.7e11 for z~2 (U)LIRGs) than those based on standard SED-fitting procedures. The stellar mass difference is larger for the most dust obscured objects. We also find lower SFRs ( A new insight into stellar populations of high redshift early-type galaxies We present a study of the star formation history of a sample of z~1 early-type galaxies (ETGs) based on the analysis of some spectral indices. The sample has been selected from a complete catalog (K<20.2) of 34 ETGs with spectroscopically identified redshift and ascertained elliptical morphology determined on HST-ACS images, in the GOODS-South area. All the galaxies of the sample have already been intensively studied on the basis of their Spectral Energy Distribution (SED) derived from 14 photometric points from UV to far-IR bands. Here we propose the analysis of their spectra obtained with FORS2-VLT in the range between 5000\AA and 10000\AA. The achieved high S/N of the analyzed spectra has allowed for the first time the measure of the blue spectral indices H+K(CaII) and Delta(4000) in a sample of high redshift ETGs. The comparison of the measured indices with the values forseen by the spectrophotometric models of Bruzual \& Charlot (2003) has allowed to derive new age estimates to be compared with those derived from the previous photometric studies.
All the galaxies of the analyzed sample result to be characterized by older ages (~5 Gyr) with respect to the ages derived by the photometric studies (< 3 Gyr). In particular, in order to simultaneously fit both the indices values and the photometric SED of all the galaxies in our sample, we introduced the hypothesis of the presence of two distinct stellar components, with markedly different ages.
We found that for all of them, more than 90% of the total stellar mass must be contained
in old stellar components (3-5 Gyr), much older than the global age derived by the photometric studies. The remaining part is composed by young components with ages younger than 1 Gyr. In particular, for some of them we found that a residual star formation activity is still ongoing, and that the young component is less than 0.1 Gyr old.
The analysis here presented demonstrates the feasibility of disentangling the past star formation time scales of high redshift ETGs from their mean stellar age (derived form the previous photometric studies) by means of the measure of the spectral indices. Furthermore, it casts some doubts on the reliability of the stellar age estimates based on the photometric studies alone. The Stellar Population of z=1.5-1.6 [OII] Emitting Galaxies Selected from Narrow-band Surveys Since the SFR density of galaxies is an order of magnitude higher at z=1-5 than in the local universe, emission-line galaxies are prominent at early epochs, and thus are useful probes of the evolution of galaxies. Current techniques to identify such emission-line galaxies include grism surveys, slit spectroscopy, and narrow-band imaging.
Narrow-band surveys, especially those made possible with Subaru, have identified large samples of star-forming galaxies by detecting their redshifted nebular emission lines, at low and high redshifts. These surveys have the ability to: (1) determine redshift to ~1 percent accuracy, (2) derive emission-line fluxes, which can be used to determine SFRs and trace the evolution of the cosmic SFR density. And they accomplish this with roughly an order-of-magnitude higher efficiency than spectroscopic surveys.
However, it is still unclear what galaxy population(s) these techniques probe or are unable to probe. In this talk, I will present new results on the stellar populations of 1,200 [OII] emitters at z=1.5-1.6 that have been identified in the Subaru Deep Field (SDF). Compared to other narrow-band surveys, the
SDF has the most sensitive imaging in six different NB filters. It is further complemented by deep multi-band imaging between 1500AA and 2 microns. With this unique dataset that probes low [OII] EW's and faint emission-line luminosities, we model their SEDs. We find that our sample span a diverse population of star-forming galaxies with typical stellar ages of 300 Myrs, stellar masses of 3X10^9 Msun, and SFRs of 10 Msun/yr. We have also compared our sample against common techniques (i.e., BX/BM and BzK) to select high-z galaxies, and find that the NB selection simultaneously spans both populations. This indicates that selection biases present in the NB samples are minimal compared to popular color selections. Such implications may apply to other emission-line surveys, especially forthcoming spectroscopic missions. Unravelling the stellar population properties of nuclei in early-type galaxies It is widely believed that 70-80% of all galaxies host nuclear star clusters (NSCs). However, only a small amount of studies about their stellar population properties exists and they are mainly focused on NSCs in late-type galaxies. Characterising the NSCs in early-type galaxies is a non trivial task, both because of the high surface brightness of the underlying galaxy, and because of their compact sizes. However, with the availability of adaptive optics fed instruments, like SINFONI, this task is less of a burden. I will present our pilot study of the nucleus of NGC1428, a nucleated elliptical galaxy in the Fornax cluster. Using the state-of-the-art stellar populations models, we explore the chemical and dynamical properties of the stellar population of the NSC, hosted by this galaxy. I will also briefly review our ongoing efforts to create a library of integrated near-IR spectra of globular clusters to serve as calibrators and test bench for current and future stellar population models.
Narrow-band selected galaxies from VISTA observations at 1.18 micron: first results The 4-meter VISTA telescope at Paranal Observatory has observed about 2 square degrees of the COSMOS field in four broad band filters (YJHKs) and in a narrow band filter at 1.18 micron (NB118). The data come from the first year of the ongoing UltraVISTA survey and from our GTO programme. The NB118 filter corresponds to Lyman alpha at z=8.8, although such galaxies are only expected to be detected in the full 5 year UltraVISTA data. The filter also selects Halpha at z=0.8, [OIII] and Hbeta at z=1.4, and [OII] at z=2.2, and the current dataset contains a large number of such foreground emitters. I will report the first results on these narrow band selected emission line galaxies.
SSP Modeling of Quasar Host Results using a Diffusion K-Means Selected Basis We now know that most galaxies have supermassive black holes (SMBH) in their centers, and somewhat unexpectedly, there are relationships\such as the M-sigma relation\between the mass of the central black hole and the velocity dispersion of the host galaxy's stellar spheroid (bulge), even though they lie outside the black hole's influence. Galaxy merger models show reasonable evidence for coevolution of the bulge and black hole since the merging process initiates simultaneous growth of the black hole and galaxy by supplying gas to the nucleus for accretion onto the black hole and triggering bursts of star formation. The merging process truncates the growth of both by removing the gas reservoir via feedback from these processes. But recently, itfs been shown that this relation could arise from central limit-like arguments alone. To really judge connections between SMBH and their host, itfs crucial to study these galaxies at the peak of black hole growth\during the quasar phase. Using 3-d spectroscopy methods, namely integral field units (IFUs), it is possible to successfully recover information about the host galaxy's integrated star formation history that can be used to check merger-induced galaxy evolution predicted by the models. But, it is critical to have a robust and careful analysis of the stellar population modeling. This research focuses on more reliably decomposing quasar host galaxy spectra into simple stellar populations (SSPs) using a statistical method called diffusion k-means to form a basis used for fitting. Results from a comparison study, using a diffusion k-means basis and a more traditional ghand-pickedh basis will be presented. The Discovery of an Ultra-Faint Globular Cluster in the Outer Halo We report the discovery of a new ultra-faint globular cluster in the constella-
tion of Ursa Minor, based on stellar photometry from the MegaCam imager at the Canada-France-Hawaii Telescope (CFHT). We find that this cluster, Munoz 1, is located at a distance of 45 } 5 kpc and at a projected distance of only 45 from the center of the Ursa Minor dSph galaxy. Using a Maximum Likelihood technique we measure a half-light radius of 0.5, or equivalently 7pc and an ellipticity consistent with being zero. We estimate its absolute magnitude to be Mv= |0.4 } 0.9, which corresponds to Lv= 120(+160,-65) L_sun, and we measure a heliocentric radial velocity of |137 } 4 km/s based on Keck/DEIMOS spectroscopy. This new satellite is separate from Ursa Minor by _ 30 kpc and 110 km/s suggesting the cluster is not obviously associated with the dSph, despite the very close angular separation. Based on its photometric properties and structural parameters we conclude that Munoz 1 is a new, outer halo ultra-faint stellar cluster. Along with Segue 3 this is one of the faintest stellar clusters known to date. The Core-Cusp problem in Cold Dark Matter halos and Supernova feedback: Effects of Oscillation The Core-Cusp problem is well known as an open question in Cold Dark Matter (CDM) cosmology. Cosmological N-body simulations have predicted that CDM halos have power-law mass-density profiles. However, recent observations have revealed a density of less-massive galaxies is constant around the center.
To solve this problem, we study possible interactions between DM particles and density waves induced by the forced oscillations of the gas driven by the supernova feedback. For example, the burst of star formation at the galactic center makes the gas hot and induces the large-scale outflow. If the expanding hot gas loses a large amount of energy by the radiative cooling, it falls back toward the galactic center. Then, the star formation occurs again at the galactic center. This cycle of expansion and contraction of the gas component have an impact on the density profile around the center of the DM halos.
In this study, we investigate the dynamical response of DM halos with a cusp to recurring changes of the baryon potential by using collision-less N-body simulations. Previous studies do not emphasize on the dependence of change in potential on a timescale, although it is directly correlated with star formation histories of galaxies. We focus on these aspects in particular and demonstrate that the region in which the core was created changes depending on the timescale. Furthermore, we compare these results with a simple analytical model of the resonance between the DM particles and the density waves of the baryon. Our results indicate that the resonance plays an important role for the cusp to core transition of the CDM halos, and can resolve the Core-Cusp problem. Moreover, we apply our resonance model to some observed galaxies and discuss the relation between their core scale and star formation histories. A better tool for studying stellar populations : Improved Spectral Line Measurements of SDSS DR7 Galaxies We present a new database of absorption and emission line measurements based on the Sloan Digital Sky Survey 7th data release for the galaxies within a redshift of 0.2. Using penalized pixel-fitting(pPXF) and GANDALF codes, we improve the existing measurements for stellar kinematics, the strength of various absorption-line features, and the flux and width of the emissions from different species of ionized gas. The absorption line strengths measured by SDSS pipeline are seriously contaminated by emission fill-in. We effectively separate emission lines from absorption lines. For instance, this work successfully extract [NI] doublet from Mgb and it leads to more realistic result of alpha enhancement of galaxies compared to the previous database. Our database is useful to study the stellar contents in galaxies and to test galaxy evolution models. We also provide new parameters that are indicative of line strength measurement quality. Users can build a subset of database optimal for their studies using specific cuts in the fitting quality parameters as well as empirical signal-to-noise. Applying these parameters, we found numerous ehiddenf broad-line-region galaxies and they turned out to be Seyfert I nuclei.
The database is publicly available at http://gem.yonsei.ac.kr/ossy & http://www.sdss.org/dr7/products/value_added/ Delay Time Distribution of TypeIa Supernovae and Galaxy Ages The Delay Time Distribution (DTD) for supernovae of Type Ia is the
rate at which supernova outbursts occur at different ages after a
burst of star formation. Here we use stellar population ages from zpeg (Le Borgne and Rocca-Volmerange 2001), and SN Ia data from the CFHT Supernova Legacy Survey (SNLS), to constrain the DTD. We use a subset of roughly 200 SNeIa with spectroscopic types and redshifts in the range 0.2-0.7 (out of a total sample of nearly 400 objects with redshifts out to 1 and beyond). From these data, and from detection efficiencies computed by Perrett et al. 2011, we derive the DTD and compare with theoretical models. We also find differences in the DTD as a function of SNIa light curve properties, possibly indicative of more than one class of SNIa progenitor. Quenching in galaxy clusters during the last 10 Gyr: role of secular evolution, galaxy mass and environment. Galaxy mass and environment are known to play a key role in galaxy evolution: looking at galaxy colors at different redshifts, fixed galaxy mass and environment, offers a powerful diagnosis to disentangle the role of each. We study at the same time the dependence of the fraction of blue galaxies on secular evolution, environment and galaxy mass with a well-controlled cluster sample spanning the last 10 Gyr (0 < z < 2). We find that the mass and environmental quenchings are separable, that environmental quenching does not change with epoch, and that mass quenching is a dynamical process. Blue Stragglers in Milky Way Satellites We have studied Blue Straggler Stars (BSSs) in different types of Galactic satellites in the outer halo: globular clusters, classical dwarf spheroidal galaxies and the recently discovered ultra-faint dwarfs (UFDs). The main goal is to characterize the BSS population in the most diffuse halo systems, where collisions are highly unlikely, thus, enabling us to test the BSS formation mechanism via mass-transfer in close binaries. Using new, deep and wide-field photometric data taken with MegaCam at the Canada-France-Hawaii Telescope we are able to assess and analyze various aspects on the nature of BSS, in both dark matter-dominated (galaxies) and dark matter-free (clusters) systems, which include specific frequencies of BSSs, correlations between these frequencies and the structural parameters of the Galactic satellites, and dominating BSS formation mechanism.
Very interestingly, we find BSSs to be ubiquitous among all different satellites.
For globular clusters, we observe an anti-correlation between BSS frequency and absolute magnitude Mv, supporting the binary origin of their BSSs.
For dwarf galaxies, we obtain a surprisingly flat BSS frequency distribution, with an overall value as high as the highest found for our clusters. This distribution further supports the binary origin for BSSs, but unlike globular clusters, it corresponds to a density regime where primordial binaries are unlikely to be unbound even in the brightest objects.
Besides a few exceptions, no spatial concentration of BSSs is observed in our systems, as expected from mass-transfer BSSs. This suggests that mass-segregation processes have not played a significant role in forming or driving BSSs. A photometric and spectroscopic study of the AGB population of NGC 6822 AGB stars represent the old and intermediate age population of a galaxy (1-10 Gyrs). Through the well known correlation between the C/M ratio (the ratio of carbon-rich to oxygen-rich AGB stars) and iron abundance we are able to study large scale metallicity variations across a galaxy. From there we can also make inferences about the age of the stellar population and derive essential information about its star formation history and the chemical evolution of the host galaxy.
Our recent work has focused on the use of the C/M vs. [Fe/H] relation in the Local Group dwarf galaxy NGC 6822. Using high quality JHK photometry the C- and M-type components of the AGB population have been isolated and an estimate made of the iron abundance, [Fe/H] = -1.29 +/- 0.07 dex. For comparison with other selection techniques we have also matched our JHK photometrically classified sources with sources classified using broad- and intermediate-band optical imaging of the NGC 6822.
Follow up spectroscopy of both the near-infrared (NIR) and optically classified sources, particularly those with differing classifications has been obtained. In addition to assessing the level of bias associated with both the optical and NIR selection of C- and M-type AGB targets, analysis of the type and strength of the various spectral lines present in these sources will help to better constrain the C/M vs. [Fe/H] relation. Furthermore, we hope to investigate a potential age-gradient observed in the AGB population during our NIR analysis. This data will also allow us to confirm the spatial extent of the AGB population in NGC 6822, which we estimate to extends ~4 kpc from the optical centre of the galaxy, forming a kind of 'halo'. This is consistent with other recent findings which suggest that halos of old- and intermediate age stars are more common in dwarf galaxies than previously thought but more work is needed to confirm this. Cluster galaxies at z~2 Galaxy cluster Cl J1449+0856 was recently discovered as an overdensity of red galaxies at z~2, associated with a faint extended X-ray emission, making it the most distant cluster discovered thus far. It allows us to extend the observation of galaxies in clusters to more than 10 billion years ago, and in a crucial epoch bridging proto-clusters to the first established clusters, thus offering us a picture of the early evolution of massive galaxies in dense environments. Massive galaxy populations in its central area seem to show remarkable diversity as compared to the generally more uniform red-sequence population dominating the high-mass end of cluster-core galaxies up to z<1.5, possibly extending recent findings on the still active galaxy formation in z>1.5 cluster cores. I will present first results from the study of stellar populations and morphological structure of massive galaxies in this unique system, our first chance to trace back the evolution of galaxies in a cluster environment close to their expected formation epoch.
Transition of the Initial Mass Function Based on Binary Population Synthesis The Initial mass function (IMF) is one of the most important factors influencing the evolution of galaxies. The current understanding of the IMF for the first stars is that it is dominated by high-mass stars, which is quite different from
the characteristics prescribed by the present-day IMF. If this is true a question arises - how and when did the IMF change?
Extremely metal-poor stars (EMP stars, defined by [Fe/H] < -2.5) observed in the Galaxy can help to answer this question. Many observations have revealed a large frequency of carbon-enhanced stars among EMP stars, the so-called CEMP stars. The subclasses of CEMP stars (CEMP-s[nos]: CEMP stars with [without] the enhancement of s-process elements; NEMP stars: nitrogen-enhanced metal-poor stars) will help to investigate the star formation history of Our Galaxy since these stars could be affected by AGB star evolution.
In this paper, we try to explain the characteristics of EMP stars using binary population synthesis. Our model includes the effect of AGB evolution and binary mass transfer for a given IMF and period distribution function of binaries. We will discuss the origins of CEMP-s, CEMP-nos, and NEMP stars with the possible effect of mass loss at low-metallicity taken into account. The proposed scenarios based on our models strongly support high-mass dominated star formation during the early epoch of the Galaxy, although the IMF also predicts
the formation of low-mass stars that survive until today. A novel finding of our study is that a significant contribution from Type 1.5 supernovae is expected due to the suppression of mass loss from intermediate-mass AGB stars. Our model also suggests that the IMF had a transition phase at [Fe/H] ~ -2. Paschen Alpha Survey of Local LIRGs using by miniTAO/ANIR ANIR (Atacama Near InfraRed camera) is a near infrared camera for the University of Tokyo Atacama 1.0m telescope, installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and extremely low water vapor (PWV=0.5mm) of the site enable us to perform observation of hydrogen Paschen alpha emission line at 1.8751 micron.
Since the first light observation carried out in June 2009, we have carried out a Paschen alpha narrow-band imaging survey of nearby luminous infrared galaxies (LIRGs), and have obtained Paschen-alpha line fluxes for 38 nearby LIRGs listed in AKARI/FIS-PSC at the velocity of recession between 2800 km/s and 8100 km/s.
LIRGs are affected by a large amount of dust extinction (Av~3mag), produced by their active star formation activities. Because Paschen-alpha emission is the strongest hydrogen recombination line in infrared wavelength ranges, it is a good and direct tracer of dust-enshrouded star forming region, and enables us to probe the star formation activities in LIRGs.
We find that the star formation rates (SFRs) estimated by the Paschen alpha luminosity corrected dust extinction by hydrogen flux ratio in optical (balmar decrement) are consistent with the SFRs estimated by AKARI bolometric infrared luminosity (AKARI SFRs). To evaluate quantity of star forming region profile, concentration index are used, and we find that LIRGs have two star forming modes. One have a star forming region profile concentrated in the center like elliptical galaxy, and another one have extended profile like the spiral or irregular. By examining the nature of galaxies each of these two modes, can be close to understanding the evolution of LIRGs.
In this presentation, we show the results of the survey and discuss the nature of local LIRGs. The Effects of AGN Feedback on Simulated Galaxies I present results of cosmological simulations performed using a version of the GADGET code that includes supernova feedback and chemical enrichment. The simulations are repeated with AGN feedback included. The effects of AGN feedback on star formation and galactic evolution are analysed. Chemical Evolution of the Galactic Bulge Formed through Two Stellar Disks Results of recent observations of the Galactic bulge demand that we discard a simple picture of its formation, suggesting the presence of two stellar populations represented by two peaks of stellar metallicity distribution (MDF) in the bulge. To assess this issue, we construct Galactic chemical evolution models that have been updated in two respects: First, the delay time distribution (DTD) of type Ia supernovae (SNe Ia) recently revealed by extensive SN Ia surveys is incorporated into the models. Second, the nucleosynthesis clock, the $s$-processing in asymptotic giant branch (AGB) stars, is carefully considered in this study. This novel model first shows that the Galaxy feature tagged by the key elements, Mg, Fe, Ba for the bulge as well as thin and thick disks is compatible with a short-delay SN Ia. We present a successful modeling of a two-component bulge including the MDF and the evolutions of [Mg/Fe] and [Ba/Mg], and reveal its origin as follows. A metal-poor component ($<$[Fe/H]$>$$\sim$-0.5) is formed with a relatively short timescale of $\sim$1 Gyr. These properties are identical to the thick disk's characteristics in the solar vicinity. Subsequently from its remaining gas mixed with a gas flow from the disk outside the bulge, a metal-rich component ($<$[Fe/H]$>$$\sim$+0.3) is formed with a longer timescale ($\sim$ 4 Gyr) together with a top-heavy initial mass function that might be identified with the thin disk component within the bulge. Resolved stellar haloes of GHOSTS galaxies In the context of hierarchical galaxy formation, stellar haloes are built up through numerous early accretion events; direct fossil record of assembly history of a galaxy is preserved in the ages, metallicities, kinematics, and spatial distributions of its halo stars. Observations of these extremely faint galaxy outskirts provide an important tool for understanding the formation and evolution of disk galaxies.
GHOSTS survey (Galaxy Halos, Outer disks, Star clusters, Thick disks, and Substructure) is the largest study of resolved stellar populations in the outskirts of disk galaxies to date, providing colour-magnitude diagrams down to ~2.5 magnitudes below the tip of the red giant branch. We trace stellar haloes down to the effective surface brightness levels of ~30 (V) mag arcsec^{-2} and projected distances of up to 50 kpc. This is the first time a stellar halo outside the Local Group has been charted out to these large galactocentric distances. We derive structural parameters of stellar haloes in the GHOSTS sample and compare these with the predictions from the cosmological simulations of galaxy formation. First r-process in the Galaxy The radioactive products of r-process, U and Th, serve as cosmo-chronometers thanks to their half-lives comparable to the age of the universe. Previous studies of the U-Th chronology estimated the age of an extremely-r-enhanced star CS 31082-001 about 14Gyr (with an error bar of 2-3Gyr), being consistent with the age of the universe. This conformed to the idea that such metal-poor stars ([Fe/H] ~ -3) had formed in the very early Galaxy. We have re-analyzed the age of this star making use of a new approach, the U-Th-Pb cosmo-chronology. An inclusion of Pb abundances (decay products of U and Th) into analyses leads to a reliable but substantially lower age of about 10-12Gyr. This indicates that the first r-process took place not in first explosive events such as massive supernovae but in more aged objects such as low-mass supernovae or binary neutron-star mergers. This also suggests that a simple age-metallcity relation cannot be applied to the early Galaxy. Studies on galaxy formation using QSO aborption line systems The QSO absorption line systems (QALs) enable us to probe the details of the gaseous
component of intervening galaxies. An absorption-selected galaxy sample would have
many advantages for the studies of galaxy properties and therefore the galaxy formation mechanisms. Recent work on nearby Lyman Limit Systems shows the example and the importance to extend such a study to high-z samples.
The number density of Lyman Limit absorption systems (LLSs) increases dramatically towards high-z, and peaks at z ~3, which is considered to be the important epoch of galaxy formation. Therefore, detecting LLS absorbers at z~3 using deep imaging would be a crucial first step towards giving direct evidences on whether the HI absorption is from inflowing cold gas or outflows, as well as good statistics on the nature and prevalence of the cold stream accretion in the young universe.
We will present here our initial results from a pilot study on the search for LLS absorbers at z~3 using Subaru telescope. Pixel-z: Substructure and Stellar Populations in Galaxies out to z~3 using Pixel Colors: Systematics We perform a pixel-by-pixel analysis on multi-color (optical and near-infrared) images of both simulated galaxies and 467 galaxies out to z~3 from the GOODS-VIMOS survey in order to study systematic effects in extracting properties of stellar populations (age, dust, metallicity and SFR) from pixel colors using the pixel-z method. The systematics studied include the effect of the input stellar population synthesis model, the form of the input star formation history assigned to each pixel's stellar populations, passband limitations and the signal-to-noise ratio in the images. In addition, we quantify differences between individual SED fits to pixels and global SED-fitting to a galaxy's colors. In terms of the effect of the choice of models, the largest impact on the age and SFR e-folding time estimates in the pixels arises from differences between the Maraston models on one hand and the Bruzual & Charlot models on the other, when optical colors are used. This results in systematic differences larger than the 2{\sigma} uncertainties in over 10 percent of all pixels in the data. The effect of restricting the available passbands is more severe. In 26 percent of pixels in the full galaxy sample, passband limitations result in systematic biases in the age estimates which are larger than the 2{\sigma} uncertainties. With this characterization of systematic effects, we then illustrate how pixel-z can be applied robustly to make detailed studies of substructure in high redshift galaxies such as (a) radial gradients of age, SFR, sSFR and dust and (b) the distribution of these properties within subcomponents such as spiral arms and clumps. Determination of stellar population parameters from high-resolution spectral fitting Up-to-date stellar population models for the interpretation of elliptical galaxies contain several assumptions, including the stellar libraries used to obtain the integrated spectral energy distribution. In particular, modern empirical libraries such as MILES, ELODIE, STELIB, are widely used and have been shown to affect the stellar population model. In this paper we assess the robustness of age, metallicity, etc. determinations for massive galaxy spectra against the use of these different libraries. We perform full spectral fitting of a range of galaxy spectra from the SDSS. The faintest among these galaxies well mimic the low signal-to-noise of halos of massive galaxies. We quantify the possible bias in population parameters carried by individual libraries and we suggest the wavelength range for performing the optimal analysis. Stellar Populations of Early-type Galaxies in the Infall Region of z=0.83 Cluster Early-type galaxies are most common objects in the universe, especially in the clusters. However, it is unclear how they formed, how they assembled, how their star formation stopped.Stellar population studies using deep spectra give us hints about above-mentioned quesitons, but in fact it is difficult observation and analysis due to faint luminosity and age-metallicity degenearcy. Galaxies in clusters are relatively well observed and their luminosity-weighted age and metallicity are determined from those spectra, but there are few works in the low density region. Galaxies in low density region at high redshift are the interesting objects to know the mechanism of star formation quenching of galaxies and the formation of clusters. We obtained deep optical spectra of about 12 red galaxies in the hinfall regionh (sub-clump) of a z = 0.83 cluster, RX J0152.7|1357 using Gemini-South / GMOS. We found stronger Balmer absortion lines for theggrouph early-type galaxies with respect to the gclusterh counter-parts. We derived their spectroscopic age and metallicity. Younger age and lower metallicity than those of central part of galaxies in sub-clump, implies that formation of those galaxies formed slowly. Derived age and metallicity (Z(Fe)) might not be consistent with local universe; i.e. they have very low metallicity compared to z = 0. It might imply those galaxies formed stars between z = 0.8 to z = 0, therefore they might not evolve gpureh passively. Direct constraints on the influence of TP-AGB stars on the SED of galaxies from NIR spectroscopy We present VLT-ISAAC NIR spectro-photometric observations of 16
post-starburst galaxies aimed at constraining the debated influence of
TP-AGB stars on the SED of galaxies with stellar ages between 0.5 and
2 Gyr (e.g. Maraston 2005, Bruzual 2007, Marigo et al. 2008), hence
critical for high-redshift studies. Post-starburst galaxies are
characterized by negligible current star formation and SED dominated
by the young stellar population formed in a recent (<2 Gyr) burst. By
selecting post-starburst galaxies with mean luminosity-weighted ages
between 0.5 and 1.5 Gyr and a broad range of metallicities (based on
SDSS optical spectroscopy), we explore the parameter space over which
the relative energy output of TP-AGB stars peaks. A key feature of the
present study is that we target galaxies at z~0.2, so that two main
spectral features of TP-AGB stars (C-molecule bandhead drops at 1.41
and 1.77 microns, not observable from the ground at z~0) move inside
the H and K atmospheric windows and can be constrained for the first
time to high accuracy. Our observations provide key constraints to
stellar population synthesis models. Our main results (Zibetti et al.,
submitted) are:
1) the NIR regions around 1.4 and 1.77 microns (rest-frame) are
featureless for all galaxies in our sample over the whole range of
relevant ages and metallicities at varience with the Maraston (2005)
models that exhibit marked drops there;
2) no NIR flux boosting is observed: the optical-NIR SEDs of our
post-SB galaxies are generally consistent with Bruzual & Charlot (2003
SSPs of corresponding light-weighted ages and metallicities, but
cannot be reproduced using Maraston (2005) SSPs.
We discuss our straightforward results in the wider context offered by
existing observationally-driven inferences and complex modelling
issues.
