WARM GAS IN THE VIRGO CLUSTER. I. DISTRIBUTION OF Lyα ABSORBERS

Abstract

The first systematic study of the warm gas (T=10^4-5 K) distribution across a\ngalaxy cluster is presented using multiple background QSOs to the Virgo\nCluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo\nvelocity range toward 9 of 12 QSO sightlines observed with Cosmic Origin\nSpectrograph, with a cluster impact parameter range of 0.36-1.65 Mpc\n(0.23-1.05R_vir). Including 18 Lya absorbers previously detected by STIS or\nGHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we\nestablish a sample of 43 absorbers towards a total of 23 background probes for\nstudying the incidence of Lya absorbers in and around the Virgo Cluster. With\nthese absorbers, we find: (1) warm gas is predominantly in the outskirts of the\ncluster and avoids the X-ray detected hot ICM. Also, Lya absorption strength\nincreases with cluster impact parameter. (2) Lya absorbing warm gas traces cold\nHI emitting gas in the substructures of the Virgo Cluster. (3) Including the\nabsorbers associated with the surrounding substructures, the warm gas covering\nfraction (100% for N_HI > 10^13.1 cm^-2) is in agreement with cosmological\nsimulations. We speculate that the observed warm gas is part of large-scale gas\nflows feeding the cluster both the ICM and galaxies.\n