How are Lyα Absorbers in the Cosmic Web Related to Gas-rich Galaxies?

Abstract

Abstract We present the correlation between Lyα absorbers and H i galaxies in the nearby universe (0.01 ≤ z ≤ 0.057). We find that Lyα absorbers are strongly correlated to H i galaxies at a projected separation of ≤0.5 Mpc and velocity separation of ≤50 km s−1. Lyα absorbers are 7.6 times more likely to be found near H i galaxies compared to a random distribution. The strength of correlations drops as the projected and/or velocity separation increases. We also find the correlation between Lyα absorbers and H i galaxies to be stronger than those observed between Lyα absorbers and optically selected galaxies. There is an enhancement in the number of absorbers at velocity separations of ≤30 km s−1 from galaxies at distances larger than their viral radius. Combined with the fact that most of our galaxies are not driving strong outflows, we conclude that the absorbers at low-velocity separations are tracing reservoirs of cooler gas around galaxies. This conclusion is consistent with the predictions from cosmological simulations where faint gas from the IGM flows into the disks of galaxies leading to galaxy growth.