Abstract
ABSTRACT We present measurements of galactic outflow rates from the eagle suite of cosmological simulations. We find that gas is removed from the interstellar medium (ISM) of central galaxies with a dimensionless mass loading factor that scales approximately with circular velocity as $V_{\mathrm{c}}^{-3/2}$ in the low-mass regime where stellar feedback dominates. Feedback from active galactic nuclei causes an upturn in the mass loading for halo masses ${\gt}10^{12} \, \mathrm{M_\odot }$. We find that more gas outflows through the halo virial radius than is removed from the ISM of galaxies, particularly at low redshifts, implying substantial mass loading within the circumgalactic medium. Outflow velocities span a wide range at a given halo mass/redshift, and on average increase positively with redshift and halo mass up to $M_{200} \sim 10^{12} \, \mathrm{M_\odot }$. Outflows exhibit a bimodal flow pattern on circumgalactic scales, aligned with the galactic minor axis. We present a number of like-for-like comparisons to outflow rates from other recent cosmological hydrodynamical simulations, and show that comparing the propagation of galactic winds as a function of radius reveals substantial discrepancies between different models. Relative to some other simulations, eagle favours a scenario for stellar feedback where agreement with the galaxy stellar mass function is achieved by removing smaller amounts of gas from the ISM, but with galactic winds that then propagate and entrain ambient gas out to larger radii.
Highlights
In the modern cosmological paradigm, galaxies grow within dark matter haloes, which represent collapsed density fluctuations that in turn grow via gravitational instability from a near-homogeneous initial density field
Our objective is to measure the amount of gas that is ejected from galaxies and their associated dark matter haloes in the EAGLE simulations
We cannot infer outflow rates at a given halo mass from their prescription for active galactic nuclei (AGN) feedback, so we show their prescription for stellar feedback only
Summary
In the modern cosmological paradigm, galaxies grow within dark matter haloes, which represent collapsed density fluctuations that in turn grow via gravitational instability from a near-homogeneous initial density field. In this picture, galaxies do not form in monolithic formation events, and instead grow gradually via sustained periods of gaseous inflow from the larger-scale environment, tracing the hierarchical buildup of dark matter haloes Larson 1974; Silk & Rees 1998) These feedback mechanisms are a core element of modern phenomenological models and simulations that reproduce the observed properties of the overall galaxy population (e.g. Somerville et al 2008; Vogelsberger et al 2014; Schaye et al 2015)
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