Optically Unseen H I Detections toward the Virgo Cluster Detected in the Arecibo Legacy Fast ALFA Survey
We report the discovery by the Arecibo Legacy Fast ALFA (ALFALFA) survey of eight H I features not coincident with stellar counterparts in the Virgo Cluster region. All of the H I clouds have cz<3000 km s-1 and, if at the Virgo distance, H I masses between 1.9×107 and 1.1×109 Msolar. Four of the eight objects were reported or hinted at by previous studies and ``rediscovered'' by ALFALFA. While some clouds appear to be associated with optical galaxies in their vicinity, others show no clear association with a stellar counterpart. Two of them are embedded in relatively dense regions of the cluster and are associated with M49 and M86; they were previously known. The others are mostly located in peripheral regions of the cluster. Especially notable are a concentration of objects toward the so-called M cloud, 3°-5° to the northwest of M87, and a complex of several clouds projected roughly halfway between M87 and M49. The object referred to as VIRGOHI 21 and proposed to be a ``dark galaxy'' is also detected and shown to be a tidal feature associated with NGC 4254.