The Spread of Metals into the Low-Redshift Intergalactic Medium

Abstract

We investigate the association between galaxies and metal-enriched and metal-deficient absorbers in the local universe ($z < 0.16$) using a large compilation of FUV spectra of bright AGN targets observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. In this homogeneous sample of 18 O VI detections at $N_{\rm O\,{VI}}\geq13.5~\mathrm{cm}^{-2}$ and 18 non-detections at $N_{\rm O\,{VI}}<13.5~\mathrm{cm}^{-2}$ using Lya absorbers with ${N_{\rm H\,{I}}\geq} 10^{14}~\mathrm{cm}^{-2}$, the maximum distance O VI extends from galaxies of various luminosities is $\sim0.6$ Mpc, or $\sim5$ virial radii, confirming and refining earlier results. This is an important value that must be matched by numerical simulations, which input the strength of galactic winds at the sub-grid level. We present evidence that the primary contributors to the spread of metals into the circum- and intergalactic media are sub-$L^*$ galaxies ($0.25L^*<L<L^*$). The maximum distances that metals are transported from these galaxies is comparable to, or less than, the size of a group of galaxies. These results suggest that, where groups are present, the metals produced by the group galaxies do not leave the group. Since many O VI non-detections in our sample occur at comparably close impact parameters as the metal-bearing absorbers, some more pristine intergalactic material appears to be accreting onto groups where it can mix with metal-bearing clouds.