Abstract
We investigate how the way galaxies acquire their gas across cosmic time in cosmological hydrodynamic simulations is modified by a comprehensive physical model for baryonic feedback processes. To do so, we compare two simulations – with and without feedback – both evolved with the moving mesh code arepo. The feedback runs implement the full physics model of the Illustris simulation project, including star formation driven galactic winds and energetic feedback from supermassive black holes. We explore: (a) the accretion rate of material contributing to the net growth of galaxies and originating directly from the intergalactic medium, finding that feedback strongly suppresses the raw, as well as the net, inflow of this ‘smooth mode’ gas at all redshifts, regardless of the temperature history of newly acquired gas. (b) At the virial radius the temperature and radial flux of inflowing gas is largely unaffected at z = 2. However, the spherical covering fraction of inflowing gas at 0.25 rvir decreases substantially, from more than 80 per cent to less than 50 per cent, while the rates of both inflow and outflow increase, indicative of recycling across this boundary. (c) The fractional contribution of smooth accretion to the total accretion rate is lower in the simulation with feedback, by roughly a factor of 2 across all redshifts. Moreover, the smooth component of gas with a cold temperature history, is entirely suppressed in the feedback run at z < 1. (d) The amount of time taken by gas to cross from the virial radius to the galaxy – the ‘halo transit time’ – increases in the presence of feedback by a factor of ≃2–3, and is notably independent of halo mass. We discuss the possible implications of this invariance for theoretical models of hot halo gas cooling.
Highlights
Over the past decade, numerical simulations modelling the evolution of gas in a cold dark matter cosmology have made it clear that the process by which galaxies acquire their baryons across cosmic time evades a satisfactory understanding
This paper contrasts two simulations, realizations of the same initial conditions evolved with the moving mesh code AREPO
We denote this measurement Mgpa+sr, where the combined contributions from primordial and material previously cycled through the main progenitor branch’ (MPB) are two disjoint subsets of accretion which sum to the total instantaneous accretion rate
Summary
Numerical simulations modelling the evolution of gas in a cold dark matter cosmology have made it clear that the process by which galaxies acquire their baryons across cosmic time evades a satisfactory understanding. 2005) have shown that gas accretion in the cosmological context, without the luxury of spherical symmetry, is significantly more complex They found that (i) coherent streams of gas can provide strong fuelling for star formation over relatively small solid angles of the virial sphere, and (ii) such streams could potentially remain cold and avoid heating up to the virial temperature, even for haloes massive enough to support a quasi-static hot atmosphere. Such flows are a natural consequence of the ‘cosmic web’ of large-scale structure, at high redshift (z > 2), and provide an intriguing avenue for gas It has been looked at in terms of the acquisition of angular momentum (Danovich et al 2012; Stewart et al 2013; Danovich et al 2014), including the connection to preferred directions imposed by the filaments of large-scale structure (Dubois et al 2014), and the feeding of supermassive black hole (SMBH) accretion (Dubois et al 2012a; Bellovary et al 2013; Feng et al 2014)
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