Galactic Winds in Cosmological Simulations of the Circumgalactic Medium. (arXiv:1210.3582v1 [astro-ph.CO])

Galactic Winds in Cosmological Simulations of the Circumgalactic Medium. (arXiv:1210.3582v1 [astro-ph.CO]):
(Abridged) We explore new observationally-constrained sub-resolution models
of galactic outflows and investigate their impact on the circumgalactic medium
(CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic
simulations, including star formation, chemical enrichment, and four cases of
SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind
(CW), a radially varying wind (RVWa) where the outflow velocity has a positive
correlation with galactocentric distance (r), and a RVW with additional
dependence on halo mass (RVWb). Overall, we find that the outflows expel
metal-enriched gas away from galaxies, significantly quench star formation, and
enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy
centers are most sensitive to the choice of the wind model for halo masses
(10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case,
except that it substantially enriches the CGM: the carbon metallicity (Z_C) is
10 times higher in RVWb than in NW at r > R_200; and the warm gas of 10^4 -
10^5 K and delta < 100 is enriched to 50 times higher than in NW. We also find
that the impact of models CW and RVWa are similar, with the following
differences. RVWa causes a greater suppression of star formation rate at z < 5,
and has a higher fraction of low-density (delta < 10), warm-hot (10^4 - 10^6 K)
gas than in CW. Outflows in CW produce a higher and earlier enrichment of some
IGM phases than RVWa. By visual inspection, we note that the RVWa model shows
more pronounced bipolar outflows and galactic disks. We present fitting
formulae for [Z_C-delta] and [Z_C-r], also for the abundance of CIV as a
function of r. We predict observational diagnostics to distinguish between
different outflow scenarios: Z_C of the CGM gas at r = (30 - 300) kpc/h
comoving, and CIV fraction of the inner gas at r < (4 - 5) kpc/h comoving.