MUSEQuBES: mapping the distribution of neutral hydrogen around low-redshift galaxies

Abstract

ABSTRACT We present a detailed study of cool, neutral gas traced by Lyα around 4595 z < 0.5 galaxies using stacks of background quasar spectra. The galaxies are selected from our MUSEQuBES low-z survey along with data from the literature. These galaxies, with a median stellar mass of ${\rm log}_{10}(M_*/\rm {\rm M}_{\odot })$ =10.0, are probed by 184 background quasars giving rise to 5054 quasar-galaxy pairs. The median impact parameter is b = 1.5 pMpc (median b/Rvir = 10.4) with 204 (419) quasar-galaxy pairs probing b/Rvir < 1(2). We find excess absorption out to at least ≈15Rvir transverse distance and ≈±600 $\rm km~s^{-1}$ along the line of sight. We show that the median stacked profile for the full sample, dominated by the pairs with b > Rvir, can be explained by a galaxy-absorber two-point correlation function with r0 = 7.6 pMpc and γ = −1.57. There are strong indications that the inner regions (≲Rvir) of the rest equivalent width profile are better explained by a log-linear (or a Gaussian) relation, whereas the outer regions are well described by a power-law, consistent with galaxy-absorber large-scale clustering. Using a sub-sample of 339 galaxies (442 quasar-galaxy pairs, median b/Rvir = 1.6) with star formation rate measurements, we find that the Lyα absorption is significantly stronger for star-forming galaxies compared to passive galaxies, but only within the virial radius. The Lyα absorption at b ≈ Rvir for a redshift-controlled sample peaks at $M_* \sim 10^9~ {\rm {\rm M}_{\odot }}~ (M_{\rm halo} \sim 10^{11}~ \rm {\rm M}_{\odot })$.