Abstract
We present the first characterization of the diffuse gas and metals in the
circumgalactic medium of 96 z = 2.9-3.8 Ly$\alpha$ emitters (LAEs) detected
with the Multi-Unit Spectroscopic Explorer (MUSE) in fields centered on 8
bright background quasars as part of our MUSEQuBES survey. The LAEs have
relatively low Ly$\alpha$ luminosities (~$10^42$ erg/s) and star formation
rates ~1 $M_ødot$/yr, which for main sequence galaxies corresponds to stellar
masses of only ~$10^8.6$ $M_ødot$. The median transverse distance between
the LAEs and the quasar sightlines is 165 proper kpc (pkpc). We stacked the
high-resolution quasar spectra and measured significant excess HI and CIV
absorption near the LAEs out to 500 km/s and at least 250 pkpc (corresponding
to ~7 virial radii). At < 30 km/s from the galaxies the median HI and CIV
optical depths are enhanced by an order of magnitude. The average rest-frame
equivalent width of Ly$\alpha$ absorption is comparable to that for Lyman-break
galaxies (LBGs) at z~2.3 and ~L* galaxies at z~0.2, but considerably higher
than for sub-L*/dwarf galaxies at low redshift. The CIV equivalent width is
comparable to those measured for low-z dwarf galaxies and z~2.3 LBGs but
significantly lower than for z~2.3 quasar-host galaxies. The absorption is
significantly stronger around the ~ 1/3 of our LAEs that are part of "groups",
which we attribute to the large-scale structures in which they are embedded. We
do not detect any strong dependence of either the HI or CIV absorption on
transverse distance (over the range 50-250 pkpc), redshift, or the properties
of the Ly$\alpha$ emission line (luminosity, full width at half maximum, or
equivalent width). However, for HI, but not CIV, the absorption at < 100 km/s
from the LAE does increase with the star formation rate. This suggests that
LAEs surrounded by more neutral gas tend to have higher star formation rates.
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