Predicted Sizes of Pressure-Supported HI Clouds in the Outskirts of the Virgo Cluster

TL;DR

This study uses ALFALFA and X-ray data to show that starless HI clouds in Virgo are likely pressure-supported and may be on the verge of star formation, representing a transition to dwarf galaxies.

Contribution

It provides the first detailed pressure equilibrium analysis of starless HI clouds in Virgo, predicting their sizes and star formation potential.

Findings

Starless HI clumps are in pressure equilibrium with Virgo's X-ray gas.

Predicted sizes of HI clumps range from 1-10 kpc.

Most HI dark clumps are near the threshold of star formation.

Abstract

Using data from the ALFALFA Arecibo HI survey of galaxies and the Virgo cluster X-ray pressure profiles from XMM-Newton, we investigate the possibility that starless dark HI clumps, also known as "dark galaxies", are supported by external pressure in the surrounding intercluster medium. We find that the starless HI clump masses, velocity dispersions and positions allow these clumps to be in pressure equilibrium with the X-ray gas near the virial radius of the Virgo cluster. We predict the sizes of these clumps to range from 1-10 kpc, in agreement with the range of sizes found for spatially resolved HI starless clumps outside of Virgo. Based on the predicted HI surface density of the Virgo sources, as well as a sample of other similar resolved ALFALFA HI dark clumps with follow up optical/radio observations, we predict that most of the HI dark clumps are on the cusp of forming stars. These HI sources therefore mark the transition between starless HI clouds and dwarf galaxies with stars.