Julien Devriendt

Abstract:

We estimate the evolution of the contribution of galaxies to the cosmic background flux at $912 \AA$ by means of a semi-analytic model of galaxy formation and evolution. Such a modelling has been quite successful in reproducing the optical properties of galaxies. We assume hereafter the high-redshift damped Lyman-$\alpha$ (DLA) systems to be the progenitors of present day galaxies, and we design a series of models which are consistent with the evolution of cosmic comoving emissivities in the available near infrared (NIR), optical, ultraviolet (UV), and far infrared (FIR) bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman-$\alpha$ systems (DLA). We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for $0 \simeq z \le 4$. We take into account the absorption of Lyman-limit photons by HI and dust in the interstellar medium (ISM) of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by HI in the ISM is neglected. The ISM HI absorption results in a severe diminishing of this flux--by almost three orders of magnitude at high redshifts to between one and two orders at $z \simeq 0$. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at $z \simeq 0$.

Abstract:

In this paper, we report on a first estimate of the contribution of galaxies to the diffuse extragalactic background from the far-UV to the submm, based on semi--analytic models of galaxy formation and evolution. We conclude that the global multi--wavelength picture seems to be consistent provided a quite important fraction of star--formation be hidden in dust--enshrouded systems at intermediate and high--redshift. We show that, according to such models, galaxies cannot stand as important contributors to the background hydrogen-ionizing flux at high-redshift unless neutral hydrogen absorption sites are clumpy and uncorrelated with star forming regions.We briefly discuss the robustness of such a result.

Abstract:

We examine how the mass assembly of central galaxies depends on their location in the cosmic web. The HORIZON-AGN simulation is analysed at z~2 using the DISPERSE code to extract multi-scale cosmic filaments. We find that the dependency of galaxy properties on large-scale environment is mostly inherited from the (large-scale) environmental dependency of their host halo mass. When adopting a residual analysis that removes the host halo mass effect, we detect a direct and non-negligible influence of cosmic filaments. Proximity to filaments enhances the build-up of stellar mass, a result in agreement with previous studies. However, our multi-scale analysis also reveals that, at the edge of filaments, star formation is suppressed. In addition, we find clues for compaction of the stellar distribution at close proximity to filaments. We suggest that gas transfer from the outside to the inside of the haloes (where galaxies reside) becomes less efficient closer to filaments, due to high angular momentum supply at the vorticity-rich edge of filaments. This quenching mechanism may partly explain the larger fraction of passive galaxies in filaments, as inferred from observations at lower redshifts.