Séminaire/Seminar Galaxies |
| « The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys » |
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Chentao Yang |
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Understanding the nature of high-redshift dusty galaxies requires a comprehensive view of their ISM by appreciating its chemical complexity. However, the molecular ISM at high redshifts is commonly studied using only a few species beyond 12C16O. In this talk, I will present the results of a series of NOEMA and ALMA broadband line survey work at redshift z~3-5, where we detect multiple transitions of various gas tracers that help us form a comprehensive understanding of the ISM at high redshifts for the first time. I will highlight the NOEMA surveys that targeted two strongly lensed dusty galaxies observed when the Universe was less than 1.8 Gyr old: APM 08279+5255, a quasar at redshift z = 3.911, and NCv1.143, a z = 3.565 starburst galaxy. The spectral line surveys cover frequencies of hundreds of GHz in the rest frame. We report detections of multiple transitions from 17 species, namely CO, 13CO, C18O, CN, CCH, HCN, HCO+, HNC, CS, C34S, H2O, H3O+, NO, N2H+, CH, c-C3H2, as well as the vibrationally excited HCN and neutral carbon. The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the analysis of the molecular gas excitation, we find that the physical properties and the chemical imprints of the ISM are different between them: the molecular gas is more excited in APM 08279+5255, exhibiting higher molecular gas temperatures and densities compared to NCv1.143; the molecular abundances in APM 08279+5255 are akin to the values of local AGNs, showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or the X-ray-dominated regions, while NCv1.143 more closely resembles local starburst galaxies. The most significant differences between the two sources are found in H2O, where the 448 GHz H2O line is significantly brighter in APM 08279+5255, likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that, at such high column densities, FUV radiation is less important in regulating the ISM. At the same time, cosmic rays (and/or X-rays and shocks) are the key players in shaping the molecular abundances and the initial conditions of star formation. Both our observed CO isotopologues line ratios and the derived extreme ISM conditions suggest the presence of a top-heavy initial mass function. Such deep spectral line surveys open a new window to study the physics and chemistry of the ISM and the radiation field of galaxies in the early Universe.
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jeudi 9 novembre 2023 - 11:30 Salle des séminaires Évry Schatzman Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |