Large-scale gas dynamics in the adhesion model: implications for the two-phase massive galaxy formation scenario

Abstract

The mass assembly and star formation histories of massive galaxies identified at low redshift z in different cosmological hydrodynamical simulations, have been studied through a detailed follow-up backwards in time of their constituent mass elements (sampled by particles) of different types. Then, the configurations they depict at progressively higher zs have been analysed. The analyses show that these histories share common generic patterns, irrespective of particular circumstances. In any case, the results we have found are different depending on the particle type. The most outstanding differences follow. We have found that by z ~ 3.5 - 6, mass elements identified as stellar particles at z=0 exhibit a gaseous cosmic-web-like morphology with scales of ~ 1 physical Mpc, where the densest mass elements have already turned into stars by z ~ 6. These settings are in fact the densest pieces of the cosmic web, where no hot particles show up, and dynamically organized as a hierarchy of flow convergence regions, that is, attraction basins for mass flows. On the other hand, mass elements identified at the diffuse hot coronae surrounding massive galaxies at z = 0, do not display a clear web-like morphology at any z. Diffuse gas is heated when flow convergence regions go through contractive deformations, and most of it keeps hot and with low density along the evolution. To shed light on the physical foundations of the behaviour our analyses show up, as well as on their possible observational implications, these patterns have been confronted with some generic properties of singular flows as described by the adhesion model. We have found that these common patterns simulations show can be interpreted as a consequence of flow properties, that, moreover, could explain different generic observational results on massive galaxies or their samples. We briefly discuss some of them.[Abridged]