Lyα Absorbers and the Coma Cluster

Abstract

The spatial and kinematic distribution of warm gas in and around the Coma Cluster is presented through observations of Lyα absorbers using background QSOs. Updates to the Lyα absorber distribution found in Yoon et al. for the Virgo Cluster are also presented. At 0.2-2.0R _vir of Coma we identify 14 Lyα absorbers ({N}_{{H}{{I}}}={10}^12.8-15.9 {cm}}^-2) toward 5 sightlines and no Lyα absorbers along 3 sightlines within 3{{σ }_{{v}}}_coma}. For both Coma and Virgo, most Lyα absorbers are found outside the virial radius or beyond 1σ _v consistent with them largely representing the infalling intergalactic medium. The few exceptions in the central regions can be associated with galaxies. The Lyα absorbers avoid the hot ICM, consistent with the infalling gas being shock heated within the cluster. The massive dark matter halos of clusters do not show the increasing column density with decreasing impact parameter relationship found for the smaller mass galaxy halos. In addition, while the covering fraction within R _vir is lower for clusters than galaxies, beyond R _vir the covering fraction is somewhat higher for clusters. The velocity dispersion of the absorbers compared to the galaxies is higher for Coma, consistent with the absorbers tracing additional turbulent gas motions in the cluster outskirts. The results are overall consistent with cosmological simulations, with the covering fraction being high in the observations standing out as the primary discrepancy.