A comparison of young star properties with local galactic environment for LEGUS/LITTLE THINGS dwarf irregular galaxies

TL;DR

This study investigates how environmental factors influence properties of young stellar objects in dwarf irregular galaxies, finding some correlations with local pressure and gas density but no clear trend for cluster characteristics overall.

Contribution

It provides a comparative analysis of young star properties and their relation to galactic environment in dwarf irregular galaxies, highlighting the role of local pressure and gas density.

Findings

Massive OB associations are found at higher pressure and HI surface density.

HII region brightness correlates with higher pressure environments.

No trend of cluster characteristics with large-scale environmental properties.

Abstract

We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and Blue Compact Dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates, OB associations by mass and mass surface density, O stars by their numbers and near-ultraviolet absolute magnitudes, and HII regions by Halpha surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, HI surface density, and star formation rate surface density. We find no trend of cluster characteristics with environmental properties, implying that larger scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and HI surface density, and there is a trend of higher HII region Halpha surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas are found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of star formation rate density. However, there is an increase in the ratio of the number of clusters to number of O stars with pressure, perhaps reflecting an increase in clustering properties with star formation rate.