H i observations of galaxies in the southern filament of the Virgo Cluster with the Square Kilometre Array Pathfinder KAT-7 and the Westerbork Synthesis Radio Telescope

Abstract

We map the H I distribution of galaxies in a ˜1.5 × 2.5° region located at the virial radius south of the Virgo Cluster using the KAT-7 and the Westerbork Synthesis Radio Telescope interferometers. Because of the different beam sizes of the two telescopes, a similar column density sensitivity of NH I ˜ 1 × 1018 atoms cm- 2 was reached with the two observations over 16.5 km s-1. We pioneer a new approach to combine the observations and take advantage of their sensitivity to both the large- and small-scale structures. Out to an unprecedented extent, we detect an H I tail of ˜60 kpc being stripped off NGC 4424, a peculiar spiral galaxy. The properties of the galaxy, together with the shape of the tail, suggest that NGC 4424 is a post-merger galaxy undergoing ram pressure stripping as it falls towards the centre of the Virgo Cluster. We detect a total of 14 galaxies and three H I clouds lacking optical counterparts. One of the clouds is a new detection with an H I mass of 7 × 107 M⊙ and a strong H I profile with W50 = 73 km s-1. We find that 10 out of the 14 galaxies present H I deficiencies not higher than those of the cluster's late spirals, suggesting that the environmental effects are not more pronounced in the region than elsewhere in the cluster.