GAS ACCRETION IS DOMINATED BY WARM IONIZED GAS IN MILKY WAY MASS GALAXIES AT<i>z</i>∼ 0

Abstract

We perform high-resolution hydrodynamic simulations of a Milky Way-mass\ngalaxy in a fully cosmological setting using the adaptive mesh refinement code,\nEnzo, and study the kinematics of gas in the simulated galactic halo. We find\nthat the gas inflow occurs mostly along filamentary structures in the halo. The\nwarm-hot (10^5 K &lt; T &lt; 10^6 K) and hot (T &gt; 10^6 K) ionized gases are found to\ndominate the overall mass accretion in the system (with dM/dt = 3-5 M_solar/yr)\nover a large range of distances, extending from the virial radius to the\nvicinity of the disk. Most of the inflowing gas (by mass) does not cool, and\nthe small fraction that manages to cool does so primarily close to the galaxy\n(R &lt;~ 20 kpc), perhaps comprising the neutral gas that may be detectable as,\ne.g., high-velocity clouds. The neutral clouds are embedded within larger,\naccreting filamentary flows, and represent only a small fraction of the total\nmass inflow rate. The inflowing gas has relatively low metallicity (Z/Z_solar &lt;\n0.2). The outer layers of the filamentary inflows are heated due to compression\nas they approach the disk. In addition to the inflow, we find high-velocity,\nmetal-enriched outflows of hot gas driven by supernova feedback. Our results\nare consistent with observations of halo gas at low z.\n