The Arecibo Legacy Fast ALFA Survey. VII. A Neutral Hydrogen Cloud Complex in the Virgo Cluster

We present observations of an H I cloud complex most likely located in the Virgo galaxy cluster, first reported by Kent et al. The complex consists of five clouds, detected in the dataset of the ALFALFA extragalactic H I survey at Arecibo. The clouds have radial velocities between cz _sun~ 480 and 610 km s^-1. At the Virgo cluster distance, they are spread over a projected span of 170 kpc and have H I masses ranging from 0.48 to 1.7 ×10⁸ M _sun. The overall H I mass of the complex is 5.1 × 10⁸ M _sun. The clouds' velocity widths vary between 50 and 250 km s^-1. New results of follow-up aperture synthesis observations conducted with the Very Large Array are also presented, which yield a higher-resolution view of two of the clouds in the complex. These two resolved clouds show no evidence of symmetry in the gas distribution or of any ordered motions. The possibility that the complex is a group of primordial objects, embedded in their own dark matter halo is thought to be unlikely. Scenarios in which the clouds have been removed from the disk of a galaxy traveling at high speed through the intracluster medium are considered. The most likely among those is thought to be one where the clouds were separated from NGC 4445 at a time >0.5 Gyr ago. The orbital velocity of the clouds and the putative parent galaxy would now be seen at a relatively large angle with respect to the line of sight.