The Environments of CO Cores and Star Formation in the Dwarf Irregular Galaxy WLM

TL;DR

This study investigates the environmental factors influencing CO core formation in the low-metallicity dwarf galaxy WLM, finding no clear environmental predictors for CO core presence despite detailed analysis of star forming regions.

Contribution

It provides the first detailed environmental characterization of CO cores in a low-metallicity dwarf galaxy, revealing that CO core formation is not strongly driven by local environmental factors.

Findings

Higher CO mass regions have higher HI surface densities.

No correlation between star formation region age and CO core mass.

CO cores are found across diverse environments without clear environmental dependence.

Abstract

The low metallicities of dwarf irregular galaxies (dIrr) greatly influence the formation and structure of molecular clouds. These clouds, which consist primarily of H$_2$, are typically traced by CO, but low metallicity galaxies are found to have little CO despite ongoing star formation. In order to probe the conditions necessary for CO core formation in dwarf galaxies, we have used the catalog of Rubio et al. (2022, in preparation) for CO cores in WLM, a Local Group dwarf with an oxygen abundance that is 13% of solar. Here we aim to characterize the galactic environments in which these 57 CO cores formed. We grouped the cores together based on proximity to each other and strong FUV emission, examining properties of the star forming region enveloping the cores and the surrounding environment where the cores formed. We find that high HI surface density does not necessarily correspond to higher total CO mass, but regions with higher CO mass have higher HI surface densities. We also find the cores in star forming regions spanning a wide range of ages show no correlation between age and CO core mass, suggesting that the small size of the cores is not due to fragmentation of the clouds with age. The presence of CO cores in a variety of different local environments, along with the similar properties between star forming regions with and without CO cores, leads us to conclude that there are no obvious environmental characteristics that drive the formation of these CO cores.