THE ORIGIN OF METALS IN THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES ATz= 3
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abstract
We present a detailed study of the metal-enriched circum-galactic medium of a
massive galaxy at z=3 using "ErisMC", a new cosmological hydrodynamic "zoom-in"
simulations of a disk galaxy with mass comparable to the Milky Way. The run
adopts a blastwave 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 mass M_vir=2.4e11 M_sun,
virial radius R_vir=48 kpc, and star formation rate 18 M_sun/yr, and its
metal-enriched CGM extends to 200 (physical) kpc from its center. Approximately
41, 9, and 50 percent of all gas-phase metals at z=3 are locked in a hot (T>
3e5 K), warm (3e5 >T> 3e4 K), and cold (T< 3e4 K) medium, respectively. We
identify three sources of heavy elements: 1) the main host, responsible for 60%
of all the metals found within 3R_vir; 2) its satellite progenitors,
responsible for 28% of all the metals within 3R_vir, and for only 5% of those
beyond 3R_vir; and nearby dwarfs, which give origin to 12% of all the metals
within 3R_vir and 95% of those beyond 3R_vir. Late (z<5) galactic "superwinds"
account for only 9% of all the metals observed beyond 2R_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 Eris along filaments via low-metallicity cold
inflows, and are ejected hot via galactic outflows at a few hundred km/s. The
outflow mass-loading factor is of order unity for the main halo, but can exceed
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 IGM as a whole. (abridged)
