MUSEQuBES: Characterizing the circumgalactic medium of redshift $\approx3.3$ Ly$\alpha$ emitters

Abstract

We present the first characterization of the circumgalactic medium of Ly$\alpha$ emitters (LAEs), using a sample of 96 $z\approx3.3$ LAEs detected with the VLT/MUSE in fields centered on 8 bright background quasars. The LAEs have low Ly$\alpha$ luminosities ($\sim 10^{42}\,\text{erg}\,\text{s}^{-1}$) and star formation rates (SFRs) $\sim 1~\text{M}_\odot\,\text{yr}^{-1}$, which for main sequence galaxies corresponds to stellar masses of only $\sim 10^{8.6}\,\text{M}_\odot$. 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 $\text{km}\,\text{s}^{-1}$ and at least $\approx 250$ pkpc (corresponding to $\approx 7$ virial radii). At $\lesssim 30~\text{km}\,\text{s}^{-1}$ from the galaxies the median HI and CIV optical depths are enhanced by an order of magnitude. The absorption is significantly stronger around the $\approx 1/3$ 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 $\approx 50-250$ 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 $\lesssim 100\,\text{km}\,\text{s}^{-1}$ from the LAE does increase with the SFR. This suggests that LAEs surrounded by more HI tend to have higher SFRs.