Star-Forming Environments Throughout the M101 Group

TL;DR

This study investigates star formation across different environments in the M101 Group using multiwavelength data, finding consistent star formation properties and no need for IMF truncation even in low-density regions.

Contribution

It provides the first detailed statistical analysis of HII regions in the M101 Group, showing invariance in star formation indicators across environments and supporting a universal IMF.

Findings

Median and scatter of F_Hα/F_FUV are invariant across environments.

Starburst99 models reproduce observed flux ratios with a standard IMF.

No evidence for IMF truncation in low-density star-forming regions.

Abstract

We present a multiwavelength study of star formation within the nearby M101 Group, including new deep H$\alpha$ imaging of M101 and its two companions. We perform a statistical analysis of the H$\alpha$ to FUV flux ratios in HII regions located in three different environments: M101's inner disk, M101's outer disk, and M101's lower mass companion galaxy NGC~5474. We find that, once bulk radial trends in extinction are taken into account, both the median and scatter in F$_{\rm H\alpha}/$F$_{\rm FUV}$ in HII regions are invariant across all of these environments. Also, using Starburst99 models, we are able to qualitatively reproduce the distributions of F$_{\rm H\alpha}/$F$_{\rm FUV}$ throughout these different environments using a standard Kroupa IMF, hence we find no need to invoke truncations in the upper mass end of the IMF to explain the young star-forming regions in the M101 Group even at extremely low surface density. This implies that star formation in low density environments differs from star formation in high density environments only by intensity and not by cloud-to-cloud physics.