Star-forming Environments throughout the M101 Group

Abstract

We present a multiwavelength study of star formation within the nearby M101 Group, including new deep H α imaging of M101 and its two companions. We perform a statistical analysis of the H α -to-FUV flux ratios in H ii 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 H α / F FUV in H ii regions are invariant across all of these environments. Also, using Starburst99 models, we are able to qualitatively reproduce the distributions of F H α / F FUV throughout these different environments using a standard Kroupa initial mass function (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.