High resolution observations of 'dark' neutral hydrogen clouds in the Virgo cluster with the Very Large Array

TL;DR

This study used high-resolution VLA observations to investigate dark neutral hydrogen clouds in the Virgo cluster, revealing some as dispersing gas clouds and none as stable dark galaxies, providing insights into their nature and lifecycle.

Contribution

It provides the first high-resolution VLA analysis of dark HI clouds in Virgo, distinguishing between dispersing clouds and potential dark galaxies.

Findings

Detected compact HI in two sources with optical counterparts.

Identified extended HI emission in two sources, likely dispersing.

Non-detections set limits on stable dark galaxy presence.

Abstract

We have observed six `dark' neutral hydrogen (HI) clouds discovered in the Virgo cluster by the Arecibo Galaxy Environment Survey (AGES) with the Karl G. Jansky Very Large Array (VLA), giving higher angular and velocity resolution than the original AGES observations. We detected compact HI emission in two of the sources, AGESVC1 231 and AGESVC1 274, allowing us to firmly associate them with faint ($m_g > 18.5$), blue ($g-i < 0.1$) optical counterparts with high $M_{HI}/L_g$ ratios. In a further two sources, we detected low column-density extended HI emission, consistent with these being dispersing clouds from ram-pressure stripping or tidal interactions. The final two sources were not detected with the VLA, allowing us to set low column-density limits on the HI detected by AGES that are consistent with these clouds also being formed from HI that is dispersing into the intra-cluster medium. The four HI sources not associated with optical counterparts thus appear likely to be relatively short-lived objects. No evidence was found for either pressure-supported turbulent spheres or stable dark galaxies.