The three-dimensional structure of the Virgo cluster region from Tully-Fisher and HI data

The distances and H I contents of 161 spiral galaxies in the region of the Virgo cluster are used to gain insight into the complicated structure of this galaxy system. Special attention has been paid to the investigation of the suggestion presented in an earlier work that some peripheral Virgo groups may contain strongly gas-deficient spiral galaxies. The three-dimensional galaxy distribution has been inferred from quality distance estimates obtained by averaging distance moduli based on the Tully-Fisher relationship taken from eight published data sets previously homogenized, resulting in a relation with a dispersion of 0.41 mag. Previous findings that the spiral distribution is substantially more elongated along the line of sight than in the plane of the sky are confirmed by the current data. In addition, an important east-west disparity in this effect has been detected. The overall width-to-depth ratio of the Virgo cluster region is about 1:4, with the most distant objects concentrated in the western half. The filamentary structure of the spiral population and its orientation are also reflected by the H I-deficient objects alone. The H I-deficiency pattern shows a central enhancement extending from similar to16 to 22 Mpc in line-of-sight distance; most of this enhancement arises from galaxies that belong to the Virgo cluster proper. However, significant gas deficiencies are also detected outside the main body of the cluster in a probable group of galaxies at line-of-sight distances similar to25-30 Mpc, lying in the region dominated by the southern edge of the M49 subcluster and clouds W' and W, as well as in various foreground galaxies. In the Virgo region, the H I content of the galaxies then is not a straightforward indicator of cluster membership.