Abstract
(Abridged) We study metal absorption by the circumgalactic medium of 843
$z\approx$2.4 star-forming galaxies taken from the Keck Baryonic Structure
Survey. The galaxies examined in this work lie in the fields of 15 background
QSOs, which all have high-quality Keck/HIRES spectra, with galaxy impact
parameters ranging from 35 kpc to 2 Mpc. Using the pixel optical depth
technique, we present the first galaxy-centred 2-D maps of the median
absorption by OVI, NV, CIV, CIII, and SIV, as well as updated results for HI.
At small galactocentric radii the absorption is strongly enhanced. The
enhancement extends out to at least 180 kpc for OVI, CIII and SiIV (and 2 Mpc
for HI and CIV) in the transverse direction, and $\pm$240 km/s along the line
of sight (which would correspond to ~1 Mpc in the case of pure Hubble flow).
After normalising the median absorption profiles to account for variations in
line strengths and detection limits, we find no evidence for differences in the
spatial distribution between HI and metals. We also present measurements of the
scatter in the optical depths, covering factors, and equivalent widths as a
function of projected galaxy distance. The current sample contains 318 galaxies
whose redshifts have been measured from nebular emission lines using MOSFIRE,
and have uncertainties of only ~18 km/s, compared to ~150 km/s for the previous
determinations using rest-frame UV spectra. Limiting the sample to galaxies
with nebular emission line redshifts does not decrease the extent of the
enhancement along the line of sight compared to that in the transverse
direction. This rules out redshift errors as the source of the observed
redshift-space anisotropy and thus implies that we have detected the signature
of gas peculiar velocities from infall, outflows, or virial motions for HI,
OVI, CIV, CIII, and SiIV.
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