Abstract
ABSTRACT The role of galactic wind recycling represents one of the largest unknowns in galaxy evolution, as any contribution of recycling to galaxy growth is largely degenerate with the inflow rates of first-time infalling material, and the rates with which outflowing gas and metals are driven from galaxies. We present measurements of the efficiency of wind recycling from the eagle cosmological simulation project, leveraging the statistical power of large-volume simulations that reproduce a realistic galaxy population. We study wind recycling at the halo scale, i.e. gas that has been ejected beyond the halo virial radius, and at the galaxy scale, i.e. gas that has been ejected from the interstellar medium to at least $\approx 10 \, {{\ \rm per\ cent}}$ of the virial radius. Galaxy-scale wind recycling is generally inefficient, with a characteristic return time-scale that is comparable to or longer than a Hubble time, and with an efficiency that clearly peaks at the characteristic halo mass of $M_{200} = 10^{12} \, \mathrm{M_\odot }$. Correspondingly, the majority of gas being accreted on to galaxies in eagle is infalling for the first time. Recycling is more efficient at the halo scale, with values that differ by orders of magnitude from those assumed by semi-analytical galaxy formation models. Differences in the efficiency of wind recycling with other hydrodynamical simulations are currently difficult to assess, but are likely smaller. We find that cumulative first-time gas accretion rates at the virial radius are reduced relative to the expectation from dark matter accretion for haloes with mass $M_{200} \lt 10^{12} \, \mathrm{M_\odot }$, indicating efficient preventative feedback on halo scales.
Highlights
In the modern cosmological paradigm, galaxies are thought to form within dark matter haloes, which represent collapsed density fluctuations that grew from a near-uniform density field via gravitational instability
We find that EAGLE predicts larger offsets between gaseous and dark matter accretion rates than in other simulations, most notably for haloes in the mass range 1012 < M200/ M < 1013 [where there is no effect of feedback on halo-scale accretion in the OverWhelmingly Large Simulations (OWLS), for instance; van de Voort et al 2011]
As demonstrated in Wright et al (2020), the reduction of gas accretion at the virial radius is connected primarily to the implementation of feedback processes in EAGLE, which is demonstrated by comparing halo-scale accretion rates of first-time and recycled infall between the fiducial EAGLE simulations and simulation variations with feedback and/or radiative cooling processes removed
Summary
In the modern cosmological paradigm, galaxies are thought to form within dark matter haloes, which represent collapsed density fluctuations that grew from a near-uniform density field via gravitational instability. Dark matter haloes grow gradually by the accretion of smaller haloes, and baryonic accretion on to haloes is expected to trace this process, with half of the current stellar mass density of the Universe having formed after z ≈ 1.3 (Madau & Dickinson 2014). In this picture, actively star-forming galaxies continually accrete gas from their wider environments, and this in turn helps to explain the observed chemical abundances of stars Nelson et al 2015) or by the recycling of previously ejected wind material Simulation predictions for inflows are expected to be strongly model dependent, since it has been demonstrated that feedback processes (the implementation of which remains highly uncertain in simulations) modulate gaseous inflow rates, either by reducing the rate of first-time gaseous infall (e.g. Nelson et al 2015) or by the recycling of previously ejected wind material (e.g. Oppenheimer et al 2010)
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