Implications on star-formation-rate indicators from HII regions and diffuse ionised gas in the M101 Group
A. E. Watkins, J. C. Mihos, P. Harding, R. Garner III
arXiv:2404.19003v1 Announce Type: new
Abstract: We examine the connection between diffuse ionised gas (DIG), HII regions, and field O and B stars in the nearby spiral M101 and its dwarf companion NGC 5474 using ultra-deep H$alpha$ narrow-band imaging and archival GALEX UV imaging. We find a strong correlation between DIG H$alpha$ surface brightness and the incident ionising flux leaked from the nearby HII regions, which we reproduce well using simple Cloudy simulations. While we also find a strong correlation between H$alpha$ and co-spatial FUV surface brightness in DIG, the extinction-corrected integrated UV colours in these regions imply stellar populations too old to produce the necessary ionising photon flux. Combined, this suggests that HII region leakage, not field OB stars, is the primary source of DIG in the M101 Group. Corroborating this interpretation, we find systematic disagreement between the H$alpha$- and FUV-derived star formation rates (SFRs) in the DIG, with SFR$_{{rm H}alpha} arXiv:2404.19003v1 Announce Type: new
Abstract: We examine the connection between diffuse ionised gas (DIG), HII regions, and field O and B stars in the nearby spiral M101 and its dwarf companion NGC 5474 using ultra-deep H$alpha$ narrow-band imaging and archival GALEX UV imaging. We find a strong correlation between DIG H$alpha$ surface brightness and the incident ionising flux leaked from the nearby HII regions, which we reproduce well using simple Cloudy simulations. While we also find a strong correlation between H$alpha$ and co-spatial FUV surface brightness in DIG, the extinction-corrected integrated UV colours in these regions imply stellar populations too old to produce the necessary ionising photon flux. Combined, this suggests that HII region leakage, not field OB stars, is the primary source of DIG in the M101 Group. Corroborating this interpretation, we find systematic disagreement between the H$alpha$- and FUV-derived star formation rates (SFRs) in the DIG, with SFR$_{{rm H}alpha}