| Abstract |
We compare mid-infrared (mid-IR), extinction-corrected H$\alpha$, and CO (2-1) emission at 70--160 pc resolution in the first four PHANGS-JWST targets. We report correlation strengths, intensity ratios, and power law fits relating emission in JWST's F770W, F1000W, F1130W, and F2100W bands to CO and H$\alpha$. At these scales, CO and H$\alpha$ each correlate strongly with mid-IR emission, and these correlations are each stronger than the one relating CO to H$\alpha$ emission. This reflects that mid-IR emission simultaneously acts as a dust column density tracer, leading to the good match with the molecular gas-tracing CO, and as a heating tracer, leading to the good match with the H$\alpha$. By combining mid-IR, CO, and H$\alpha$ at scales where the overall correlation between cold gas and star formation begins to break down, we are able to separate these two effects. We model the mid-IR above $I_\nu = 0.5$~MJy sr$^{-1}$ at F770W, a cut designed to select regions where the molecular gas dominates the interstellar medium (ISM) mass. This bright emission can be described to first order by a model that combines a CO-tracing component and an H$\alpha$-tracing component. The best-fitting models imply that $\sim 50\%$ of the mid-IR flux arises from molecular gas heated by the diffuse interstellar radiation field, with the remaining $\sim 50\%$ associated with bright, dusty star forming regions. We discuss differences between the F770W, F1000W, F1130W bands and the continuum dominated F2100W band and suggest next steps for using the mid-IR as an ISM tracer. |
| Authors |
Adam K. Leroy  , Karin Sandström , Erik Rosolowsky , Francesco Belfiore , Alberto D. Bolatto , Yixian Cao , Eric W. Koch , E. Schinnerer , Ashley T. Barnes , Ivana Bešlić , Frank Bigiel , Guillermo A. Blanc , Jérémy Chastenet , Ness Mayker Chen , Mélanie Chevance , Ryan Chown , Enrico Congiu , Daniel A. Dale  , Oleg V. Egorov , Éric Emsellem , Cosima Eibensteiner , Christopher M. Faesi , Simon C. O. Glover , Kathryn Grasha , Brent Groves , Hamid Hassani , Jonathan D. Henshaw , Annie Hughes , María J. Jiménez-Donaire , Jaeyeon Kim , Ralf S. Klessen , Kathryn Kreckel , J. M. Diederik Kruijssen , Kirsten L. Larson , Janice Lee , Rebecca C. Levy , Daizhong Liu , Laura A. Lopez , Sharon E. Meidt , E. J. Murphy , Justus Neumann , Ismael Pessa , J. Pety , Tomoka Tosaki , Amy Sardone , Jiayi Sun , David A. Thilker , A. Usero , Elizabeth J. Watkins , Cory M. Whitcomb , Thomas G. Williams
|
