An HI survey of the Centaurus and Sculptor Groups - Constraints on the space density of low mass galaxies

TL;DR

This study used sensitive 21-cm HI surveys of the Centaurus and Sculptor groups to search for low-mass galaxies, finding none beyond known members, thus constraining the abundance of such objects and supporting dark matter models predicting many low-mass sub-halos.

Contribution

The paper provides the most sensitive extragalactic HI survey to date in these groups, setting new limits on the space density of low-mass, HI-rich galaxies and testing dark matter sub-halo predictions.

Findings

No new HI clouds or galaxies detected beyond known members.

Results support the absence of a large population of HI-rich low-mass satellites.

Constraints challenge models predicting numerous low-mass dark matter sub-halos.

Abstract

We present results of two 21-cm HI surveys performed with the Australia Telescope Compact Array in the nearby Centaurus A and Sculptor galaxy groups. These surveys are sensitive to compact HI clouds and galaxies with HI masses as low as 3E+06 Msun, and are therefore among the most sensitive extragalactic HI surveys to date. The surveys consist of sparsely spaced pointings that sample approximately 2% of the groups' area on the sky. We detected previously known group members, but we found no new HI clouds or galaxies down to the sensitivity limit of the surveys. If the HI mass function had a faint end slope of alpha = 1.5 below M_{HI} = 10^{7.5} Msun in these groups, we would have expected ~3 new objects. Cold dark matter theories of galaxy formation predict the existence of a large number low mass DM sub-halos that might appear as tiny satellites in galaxy groups. Our results support and extend similar conclusions derived from previous HI surveys that a HI rich population of these satellites does not exist.