HI Observations of Galaxies in the Southern Filament of the Virgo Cluster with the SKA Pathfinder KAT-7 and the WSRT

TL;DR

This study maps the neutral hydrogen distribution around galaxies near the Virgo Cluster using KAT-7 and WSRT, revealing new features like an extended Hi tail and isolated Hi clouds, and providing insights into galaxy interactions and environmental effects.

Contribution

It introduces a novel method to combine KAT-7 and WSRT data, enabling detailed mapping of large-scale Hi structures in a galaxy cluster environment.

Findings

Detected an unprecedented 60 kpc Hi tail from NGC 4424.

Discovered 3 Hi clouds without optical counterparts.

Most galaxies show Hi deficiencies similar to other cluster spirals.

Abstract

We map the Hi distribution of galaxies in a $\sim 1.5^\circ \times 2.5^\circ$ region located at the virial radius south of the Virgo cluster using the KAT$-$7 and the WSRT interferometers. Because of the different beam sizes of the two telescopes, a similar column density sensitivity of $\rm N_{Hi} \sim 10^{18}\,cm^{-2}$ was reached with the two observations over 16.5 km/s. 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 Hi tail of $\sim 60$ 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 a ram pressure stripping as it falls towards the centre of the Virgo Cluster. We detect a total of 14 galaxies and 3 Hi clouds lacking optical counterparts. One of the clouds is a new detection with an Hi mass of $\rm 7\times10^7\, M_\odot$ and a strong Hi profile with $W_{50} = 73$ km/s. We find that 10 out of the 14 galaxies present Hi 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.