Comparing the pre-SNe feedback and environmental pressures for 6000 HII regions across 19 nearby spiral galaxies

Abstract

The feedback from young stars (i.e. pre-supernova) is thought to play a crucial role in molecular cloud destruction. In this paper, we assess the feedback mechanisms acting within a sample of 5810 HII regions identified from the PHANGS-MUSE survey of 19 nearby ($<$ 20 Mpc) star-forming, main sequence spiral galaxies (log($M_{\star }$/M${}_{\odot }$)= 9.4 $-$ 11). These optical spectroscopic maps are essential to constrain the physical properties of the HII regions, which we use to investigate their internal pressure terms. We estimate the photoionised gas ($P_{\mathrm{therm}}$), direct radiation ($P_{\mathrm{rad}}$), and mechanical wind pressure ($P_{\mathrm{wind}}$), which we compare to the confining pressure of their host environment ($P_{\mathrm{de}}$). The HII regions remain unresolved within our $\sim 50-100$ pc resolution observations, so we place upper ($P_{\max }$) and lower ($P_{\min }$) limits on each of the pressures by using a minimum (i.e. clumpy structure) and maximum (i.e. smooth structure) size, respectively. We find that the $P_{\max }$ measurements are broadly similar, and for $P_{\min }$ the $P_{\mathrm{therm}}$ is mildly dominant. We find that the majority of HII regions are over-pressured, $P_{\mathrm{tot}}/P_{\mathrm{de}}=(P_{\mathrm{therm}}+P_{\mathrm{wind}}+P_{\mathrm{rad}})/P_{\mathrm{de}}>1$, and expanding, yet there is a small sample of compact HII regions with $P_{\mathrm{tot},\max }/P_{\mathrm{de}}<1$ ($\sim$1% of the sample). These mostly reside in galaxy centres ($R_{\mathrm{gal}}<1$kpc), or, specifically, environments of high gas surface density; log($\hat{I}{\pounds }_{\mathrm{gas}}/{\mathrm{M}}_{\odot }{\mathrm{pc}}^{-2}$)$\sim$2.5 (measured on kpc-scales). Lastly, we compare to a sample of literature measurements for $P_{\mathrm{therm}}$ and $P_{\mathrm{rad}}$ to investigate how dominant pressure term transitions over around 5dex in spatial dynamic range and 10 dex in pressure.

28 pages total, 16+3 figures, and 3 tables. Accepted for publication in MNRAS