"Dark galaxies" and local very metal-poor gas-rich galaxies: possible interrelations

TL;DR

This paper explores the possible connection between dark galaxy candidates and local very metal-poor, gas-rich dwarf galaxies, suggesting that interactions may trigger starbursts and transform dark galaxies into visible ones.

Contribution

It proposes a link between dark galaxies and metal-poor dwarfs, highlighting the role of interactions and gas instabilities in galaxy evolution.

Findings

Many metal-poor dwarfs show signs of interactions and mergers.

Some gas-rich dwarfs lack old stars, resembling dark galaxies.

Interactions may trigger starbursts and galaxy transformation.

Abstract

There are only a few ``dark galaxy'' candidates discovered to date in the local Universe. One of the most prominent of them is the SW component of a merging system HI 1225+01. On the other hand, the number of known very metal-poor gas-rich dwarfs similar to IZw18 and SBS 0335-052 E,W has grown drastically during the last decade, from a dozen and a half to about five dozen. Many of them are very gas-rich, having from ~90 to 99% of all baryons in gas. For some of such objects that have the deep photometry data, no evidences for the light of old stars are found. At least a half of such galaxies with the prominent starbursts have various evidences of interactions, including advanced mergers. This suggests that a fraction of this group objects can be a kind of very stable protogalaxies (or ``dark galaxies''), which have recently experienced strong disturbances from nearby massive galaxy-size bodies. Such a collision caused the gas instabilities and its collapse with the subsequent onset of starburst. We briefly discuss the morphology and gas kinematics for the subsample of the most metal-poor dwarfs that illustrate this picture. We discuss also the relation of these rare galaxies to the processes by which ``dark galaxies'' can occasionally transform to optically visible galaxies.