The large-scale distribution of late-type galaxies between Virgo and the Great Wall

Abstract

Neutral hydrogen data are presented for 88 of the Virgo Cluster Catalog galaxies thought on morphological grounds to lie in the background of the cluster. We confirm that the morphological assignment of cluster membership works quite well; very few of the "background" galaxies are in fact at cluster redshifts. The resulting sample of redshifts, along with optical redshifts from the literature, allow us to explore the large-scale distribution of galaxies in the space between the Local Supercluster and the Great Wall. Galaxies in a larger window around the Virgo Cluster, but at redshifts between Virgo and the Great Wall, have a fairly low average number density, but the distribution is far from uniform: Some portions resemble voids, but in other portions galaxies can be assigned to clouds or filaments of appreciable size (sometimes containing bound groups). We investigate the luminosity function in high- and low-density regions of our galaxy sample, which excludes the Virgo Cluster proper. We find no significant difference. However, our selection procedures are insensitive to galaxies of very low surface brightness, which have been reported to be more abundant in low- density regions. The average probability of a line of sight intersecting the optical disk of our sample galaxies is derived separately for the Virgo Supercluster region (redshifts below 3500 km s^-1^) and for the region behind (out to 10,000 km s^-1^). The number density ratio of Lyα forest lines to galaxies is larger by a factor of order 10 in the far (low-density) region than in the near. A survey of recent literature on galaxy redshifts uncovers a new candidate, MCG 0-32-16, for the lowest redshift absorption line.