Séminaire Doctoral / Seminar PhD |
| « Cosmological simulations from the large-scale structure to the merger of massive black holes, » |
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Chi An Dong Paez |
| Massive black holes (MBHs) inhabit the centre of most massive galaxies. Following the merger of two galaxies, the two central MBHs may sink to the centre of the new potential, form a binary, and eventually merge. Detecting the gravitational waves (GWs) and electromagnetic (EM) waves from MBH mergers can provide valuable information about the population of merging MBHs, their astrophysical environments, and more generally about the cosmic evolution of MBHs and their host galaxies. The future Laser Interferometer Space Antenna (LISA) will be targeted at detecting the GWs from MBH mergers. Before LISA flies, it is important to understand how GW and EM measurements can inform us about the physics of MBH evolution and mergers and what population of MBH mergers LISA and the future EM telescopes could detect. In this thesis, I aim to understand the properties of the population of merging MBHs and the prospects of their detection with the next generation of instruments. Using the high-redshift MBH population in a high-resolution cosmological hydrodynamical simulation, I found that merging MBHs tend be in more massive galaxies (which have a higher probability of hosting MBHs and shorter MBH dynamical evolution) than global population of MBHs. LISA can detect most of the mergers in the sample with up to high redshifts. While in the rest-frame ultraviolet (observer-frame optical/near-infrared) the light from the host tends to outshine the remnant MBH, the remnants are in some cases bright in the X-ray and radio frequencies to outshine their host and be detected. A joint detection of GW and EM emission is possible. However, for our high-redshift sample, GWs do not provide tight constraints on the sky position of the source that could aid the search for an EM counterpart. The population of EM-detected mergers is biased toward high MBH and host masses, high accretion rates and low redshifts compared to the overall population of MBH mergers. The burst of GWs produced by the merger of two MBHs can carry linear momentum if there are any asymmetries in the configuration of the system (different masses or misaligned spins and orbital angular momentum). The remnant MBH experiences a GW recoil kick whose magnitude can be larger than the escape velocity of the galaxy: it can have a profound impact on the evolution of MBHs. I investigate GW recoil in a cosmic environment by running cosmological simulations that model GW recoil kicks, calculated according to the spins, masses and angular momentum of the binary obtained on the fly. I confirmed that recoil can hinder the growth of MBHs and decrease the MBH merger rate. Even in massive gas-rich galaxies, the alignment of the spins and the MBH orbital angular momentum is not perfect in a realistic setting. This means that major MBH mergers can produce large kicks (~1000 km/s) in a wide variety of astrophysical scenarios. Recoil kicks can eject the MBH from the centre of the galaxy or the host halo. Recoiling MBHs tend to either stay in the centre of their host or get ejected on a short time scale. Only MBHs that get kicks close to the escape velocity take longer times to escape or return to the centre. Recoiling MBHs are a non-negligible fraction of the population of wandering MBHs. Even if some recoiling MBH retain their initial radial orbits, in some cases the asymmetric and clumpy potentials of realistic high-redshift haloes partly erase their initial dynamical properties: recoiling MBHs cannot always be discriminated from other wandering MBHs uniquely from their dynamics. During this thesis, I also used a large cosmological N-body simulation to produce a set of mock galaxy catalogues for cosmology. These catalogues were validated and used to obtain cosmological constraints from the Sloan Digital Sky Survey. I demonstrated that our method can produce high-fidelity mock galaxy catalogues for the analysis of very large surveys such as the ongoing Dark Energy Spectroscopic Instrument survey. |
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vendredi 4 octobre 2024 - 16:00 Salle des séminaires Évry Schatzman, Institut d'Astrophysique |
| Page web du séminaire / Seminar's webpage |