Warm Gas in the Virgo Cluster: I. Distribution of Lya Absorbers
  The first systematic study of the warm gas (T=10^4-5 K) distribution across a
galaxy cluster is presented using multiple background QSOs to the Virgo
Cluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo
velocity range toward 9 of 12 QSO sightlines observed with Cosmic Origin
Spectrograph, with a cluster impact parameter range of 0.36-1.65 Mpc
(0.23-1.05R_vir). Including 18 Lya absorbers previously detected by STIS or
GHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we
establish a sample of 43 absorbers towards a total of 23 background probes for
studying the incidence of Lya absorbers in and around the Virgo Cluster. With
these absorbers, we find: (1) warm gas is predominantly in the outskirts of the
cluster and avoids the X-ray detected hot ICM. Also, Lya absorption strength
increases with cluster impact parameter. (2) Lya absorbing warm gas traces cold
HI emitting gas in the substructures of the Virgo Cluster. (3) Including the
absorbers associated with the surrounding substructures, the warm gas covering
fraction (100% for N_HI > 10^13.1 cm^-2) is in agreement with cosmological
simulations. We speculate that the observed warm gas is part of large-scale gas
flows feeding the cluster both the ICM and galaxies.
