Cold HI in faint dwarf galaxies

TL;DR

This study investigates the distribution of cold atomic hydrogen in faint dwarf irregular galaxies, revealing that cold gas correlates with recent star formation and exhibits a different relationship than classical star formation laws.

Contribution

It introduces two methods for identifying cold HI in faint dwarf galaxies and compares their effectiveness, providing new insights into cold gas and star formation correlations.

Findings

Cold HI identified by brightness temperature is more abundant than by Gaussian decomposition.

A significant fraction of cold gas overlaps with recent star formation regions.

Star formation rate density relates to HI column density with a flatter power law than the Kennicutt-Schmidt relation.

Abstract

We present the results of a study of the amount and distribution of cold atomic gas, as well its correlation with recent star formation in a sample of extremely faint dwarf irregular galaxies. Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) and its extension, FIGGS2. We use two different methods to identify cold atomic gas. In the first method, line-of-sight HI spectra were decomposed into multiple Gaussian components and narrow Gaussian components were identified as cold HI. In the second method, the brightness temperature (T_B) is used as a tracer of cold HI. We find that the amount of cold gas identified using the T_B method is significantly larger than the amount of gas identified using Gaussian decomposition. We also find that a large fraction of the cold gas identified using the T_B method is spatially coincident with regions of recent star formation, although the converse is not true. That is only a small fraction of the regions with recent star formation are also covered by cold gas. For regions where the star formation and the cold gas overlap, we study the relationship between the star formation rate density and the cold \HI column density. We find that the star formation rate density has a power law dependence on the HI column density, but that the slope of this power law is significantly flatter than that of the canonical Kennicutt-Schmidt relation.