How do galaxies acquire their mass?

Abstract

We study the growth of galaxy masses, via gas accretion and galaxy mergers. We introduce a toy model that describes (in a single equation) how much baryonic mass is accreted and retained into galaxies as a function of halo mass and redshift. In our model, the evolution of the baryons differs from that of the dark matter because 1) gravitational shock heating and AGN jets suppress gas accretion mainly above a critical halo mass of M shock ∼ 10 12 M ; 2) the intergalactic medium after reionisation is too hot for accretion onto haloes with circular velocities v circ < ∼ 40 km s −1 ; 3) stellar feedback drives gas out of haloes, mainly those with v circ < ∼ 120 km s −1 . We run our model on the merger trees of the haloes and sub-haloes of a high-resolution dark matter cosmological simulation. The galaxy mass is taken as the maximum between the mass given by the toy model and the sum of the masses of its progenitors (reduced by tidal stripping). Designed to reproduce the present-day stellar mass function of galaxies, our model matches fairly well the evolution of the cosmic stellar density. It leads to the same z = 0 relation between central galaxy stellar and halo mass as the one found by abundance matching and also as that previously measured at high mass on SDSS centrals. Our model also predicts a bimodal distribution (centrals and satellites) of stellar masses for given halo mass, in very good agreement with SDSS observations. The relative importance of mergers depends strongly on stellar mass (more than on halo mass). Massive galaxies with m stars > m crit ∼ Ω b /Ω m M shock ∼ 10 11 M acquire most of their final mass through mergers (mostly major and gas-poor), as expected from our model's shutdown of gas accretion at high halo masses. However, although our mass resolution should see the effects of mergers down to m stars 10 10.6 h −1 M , we find that mergers are rare for m stars 10 11 h −1 M . This is a consequence of the curvature of the stellar vs. halo mass relation set by the physical processes of our toy model and found with abundance matching. So gas accretion must be the dominant growth mechanism for intermediate and low mass galaxies, including dwarf ellipticals in clusters. The contribution of galaxy mergers terminating in haloes with mass M halo < M shock (thus presumably gas-rich) to the mass buildup of galaxies is small at all masses, but accounts for the bulk of the growth of ellipticals of intermediate mass (∼10 10.5 h −1 M ), which we predict must be the typical mass of ULIRGs.

The new semi-analytic code GalICS 2.0 – reproducing the galaxy stellar mass function and the Tully–Fisher relation simultaneously

“…Fig. 6 shows that the formation of galaxies is efficient only in a narrow range of halo masses, between 10 11 and a few times 10 12 M⊙, in agreement with previous studies by Bouché et al (2010), Guo et al (2010), Cattaneo et al (2011), Behroozi et al (2013) and Birrer et al (2014). Even in this mass range, it is very difficult for haloes to convert more than a third of the baryons into stars (Fig.…”

“…However, we have developed a beta version that includes the possibility of delayed mergers. The beta version computes the delay using Jiang et al (2008)'s formula for the dynamical friction timescale (see Cattaneo et al 2011 for a description of the method). Preliminary investigations with the beta version show little difference with respect to the conclusions of this article.…”

Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

“…This is significantly lower than estimates of the mass growth of galactic halos in simulations (e.g., van den Bosch 2002; Cattaneo et al 2011), which on average double the mass of galaxies since z ∼ 1.…”

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

“…Although we describe the shift in M B as a relative loss of baryons by the dwarfs, this may not be correct. Some or all of the scarcity of baryons in extreme dwarfs could be a result of the reionization of the Universe and the subsequent difficulty that tiny halos have in capturing gas (Klypin et al 1999;Bullock et al 2000;Cattaneo et al 2011).…”

“…But since faint galaxies have dense DM halos, the systems remain bound despite any baryon loss. An alternative to baryon blowout is the difficulty of capturing or holding on to baryons in lowmass DM potential wells when the Universe was reionized (Klypin et al 1999;Bullock et al 2000;Cattaneo et al 2011).…”