The SAMI Galaxy Survey: Towards an Optimal Classification of Galaxy Stellar Kinematics
Abstract:
Large galaxy samples from multi-object IFS surveys now allow for a statistical analysis of the z~0 galaxy population using resolved kinematics. However, the improvement in number statistics comes at a cost, with multi-object IFS surveys more severely impacted by the effect of seeing and lower signal-to-noise. We present an analysis of ~1800 galaxies from the SAMI Galaxy Survey and investigate the spread and overlap in the kinematic distributions of the spin parameter proxy $\lambda_{Re}$ as a function of stellar mass and ellipticity. For SAMI data, the distributions of galaxies identified as regular and non-regular rotators with $kinemetry$ show considerable overlap in the $\lambda_{Re}$-$\varepsilon_e$ diagram. In contrast, visually classified galaxies (obvious and non-obvious rotators) are better separated in $\lambda_{Re}$ space, with less overlap of both distributions. Then, we use a Bayesian mixture model to analyse the $\lambda_{Re}$-$\log(M_*/M_{\odot})$ distribution. As a function of mass, we investigate whether the data are best fit with a single kinematic distribution or with two. Below $\log(M_*/M_{\odot})$~10.5 a single beta distribution is sufficient to fit the complete $\lambda_{Re}$ distribution, whereas a second beta distribution is required above $\log(M_*/M_{\odot})$~10.5 to account for a population of low-$\lambda_{Re}$ galaxies, presenting the cleanest separation of the two populations. We apply the same analysis to mock-observations from cosmological simulations. The mixture model predicts a bimodal $\lambda_{Re}$ distribution for all simulations, albeit with different positions of the $\lambda_{Re}$ peaks and with different ratios of both populations. Our analysis validates the conclusions from previous, smaller IFS surveys, but also demonstrates the importance of using kinematic selection criteria that are dictated by the quality of the observed or simulated data.The angular momentum of baryons and dark matter halos revisited
Abstract:
Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive mesh refinement, we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r=0.1rvir. In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/rvir>0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons remains close to that of dark matter halos. We propose a new scenario where gas efficiently carries the angular momentum generated by large-scale structure motions deep inside dark matter halos, redistributing it only in the vicinity of the disc.The diverse galaxy counts in the environment of high-redshift massive black holes in Horizon-AGN
Abstract:
High-redshift quasars are believed to reside in highly biased regions of the Universe, where black hole (BH) growth is sustained by an enhanced number of mergers and by being at the intersection of filaments bringing fresh gas. This assumption should be supported by an enhancement of the number counts of galaxies in the field of view of quasars. While the current observations of quasar environments do not lead to a consensus on a possible excess of galaxies, the future missions JWST, WFIRST, and Euclid will provide new insights on quasar environments, and will substantially increase the number of study-cases. We are in a crucial period, where we need to both understand the current observations and predict how upcoming missions will improve our understanding of BH environments. Using the large-scale simulation Horizon-AGN, we find that statistically the most massive BHs reside in environments with the largest number counts of galaxies. However, we find a large variance in galaxy number counts, and some massive BHs do not show enhanced counts in their neighborhood. Interestingly, some massive BHs have a very close galaxy companion but no further enhancement of the galaxy number counts at larger scales, in agreement with recent observations. We find that AGN feedback in the surrounding galaxies is able to decrease their luminosity and stellar mass, and therefore to make them un-observable when using restrictive galaxy selection criteria. Radiation from the quasars can spread over large distances, which could affect the formation history of surrounding galaxies, but a careful analysis of these processes requires radiative transfer simulations.The environment and host haloes of the brightest z~6 Lyman-break galaxies
Abstract:
By studying the large-scale structure of the bright high-redshift Lyman-break galaxy (LBG) population it is possible to gain an insight into the role of environment in galaxy formation physics in the early Universe. We measure the clustering of a sample of bright ($-22.7The evolution of galaxies in the early Universe with the next generation of telescopes
Abstract:
In this thesis, I present results on the statistical properties of luminous star-forming galaxies in the early Universe, spanning the first two billion years of cosmic time. I combine deep, degree-scale optical and near-infrared imaging from the latest ground-based surveys with next-generation observatories - Euclid, which provides deep, degree-scale space-based near-infrared imaging for the first time, and JWST, which delivers unrivalled depth and resolution in the near-infrared and infrared. With this unique combination, I place strong constraints on the number densities and size-scaling relations of the first galaxies.
First, by combining imaging from the VISTA telescope with deep ground-based optical surveys, infrared imaging from Spitzer/IRAC, and early data from Euclid, I construct a sample of galaxy candidates at redshift 6.5 < z < 7.5 spanning a rest-UV absolute magnitude range of −23.5 ≤ Muv ≤ −20.2. These sources represent some of the most luminous and massive galaxies at this epoch. After accounting for brown dwarf contamination through a careful SED-fitting analysis, I find that the rest-frame UV luminosity function at z ≃ 7 is best described by double-power law, showing an excess relative to a Schechter function at absolute rest-UV magnitudes Muv ≲ −22.5 and evolving slowly from z ≃ 8. This suggests that luminous galaxies at this epoch are not yet significantly affected by dust obscuration or mass quenching, and that active galactic nuclei do not contribute significantly to the luminosity function until very bright magnitudes (Muv < −24).
I then measure the size-scaling relations of 1,668 luminous galaxies at z ≃ 3 − 5 using the JWST PRIMER survey. These sources were selected from ground-based, seeing-dominated imaging, presenting an unbiased sampling of the morphology and size distributions of luminous sources. I find a build-up of large (Re > 2 kpc) galaxies at z = 3 relative to z = 4 − 5, a redshift-dependent size evolution leading to larger mean sizes at z = 3, and an increase in the intrinsic scatter of the size-mass relations towards lower redshift. These results suggest that by z = 3, some galaxies have undergone dissipative processes such as mergers and gas accretion, allowing for the formation of rare, larger galaxies. However, the majority of galaxies remain compact over this redshift range, with a typical (modal) size of Re = 0.7 − 0.9 kpc. Finally, I find that the size-mass and size-luminosity relations are consistent with predictions from simulations such as Illustris and FLARES, providing evidence for centrally concentrated star formation in the most massive galaxies at high redshift.