The origin of metals in the circumgalactic medium of massive galaxies at z = 3

Abstract

We present a detailed study of the metal-enriched circumgalactic medium (CGM) of a massive galaxy at z = 3 using results from "ErisMC," a new cosmological hydrodynamic "zoom-in" simulation of a disk galaxy with mass comparable to the Milky Way. The reference run adopts a blast wave scheme for supernova feedback that generates galactic outflows without explicit wind particles, a star formation recipe based on a high gas density threshold and high-temperature metal cooling. ErisMC's main progenitor at z = 3 resembles a "Lyman break" galaxy of total mass M vir = 2.4 × 1011 M·, virial radius R vir = 48 kpc, and star formation rate 18 M· yr-1, and its metal-enriched CGM extends as far as 200 (physical) kpc from its center. Approximately 41%, 9%, and 50% of all gas-phase metals at z = 3 are locked in a hot (T > 3 × 105 K), warm (3 × 105 K > T > 3 × 104 K), and cold (T < 3 × 104 K) medium, respectively. We identify three sources of heavy elements: (1) the main host, responsible for 60% of all the metals found within 3 R vir; (2) its satellite progenitors, which shed their metals before and during infall, and are responsible for 28% of all the metals within 3 R vir, and for only 5% of those beyond 3 R vir; and (3) nearby dwarfs, which give origin to 12% of all the metals within 3 R vir and 95% of those beyond 3 R vir. Late (z < 5) galactic "superwinds" - the result of recent star formation in ErisMC - account for only 9% of all the metals observed beyond 2 R vir, the bulk having been released at redshifts 5 ≲ z ≲ 8 by early star formation and outflows. In the CGM, lower overdensities are typically enriched by "older," colder metals. Heavy elements are accreted onto ErisMC along filaments via low-metallicity cold inflows and are ejected hot via galactic outflows at a few hundred km s -1. The outflow mass-loading factor is of order unity for the main halo, but can exceed a value of 10 for nearby dwarfs. We stress that our "zoom-in" simulation focuses on the CGM of a single massive system and cannot describe the enrichment history of the intergalactic medium as a whole by a population of galaxies with different masses and star formation histories. © 2012. The American Astronomical Society. All rights reserved.