학술논문
PHANGS-JWST First Results: Mid-infrared emission traces both gas column density and heating at 100 pc scales
Document Type
Working Paper
Author
Leroy, Adam K.; Sandstrom, Karin; Rosolowsky, Erik; Belfiore, Francesco; Bolatto, Alberto D.; Cao, Yixian; Koch, Eric W.; Schinnerer, Eva; Barnes, Ashley. T.; Bešlić, Ivana; Bigiel, F.; Blanc, Guillermo A.; Chastenet, Jérémy; Chen, Ness Mayker; Chevance, Mélanie; Chown, Ryan; Congiu, Enrico; Dale, Daniel A.; Egorov, Oleg V.; Emsellem, Eric; Eibensteiner, Cosima; Faesi, Christopher M.; Glover, Simon C. O.; Grasha, Kathryn; Groves, Brent; Hassani, Hamid; Henshaw, Jonathan D.; Hughes, Annie; Jiménez-Donaire, María J.; Kim, Jaeyeon; Klessen, Ralf S.; Kreckel, Kathryn; Kruijssen, J. M. Diederik; Larson, Kirsten L.; Lee, Janice C.; Levy, Rebecca C.; Liu, Daizhong; Lopez, Laura A.; Meidt, Sharon E.; Murphy, Eric J.; Neumann, Justus; Pessa, Ismael; Pety, Jérôme; Saito, Toshiki; Sardone, Amy; Sun, Jiayi; Thilker, David A.; Usero, Antonio; Watkins, Elizabeth J.; Whitcomb, Cory M.; Williams, Thomas G.
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Subject
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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.
Comment: 49 pages, 17 figures, Section 8 provides a detailed summary, accepted for publication in ApJ Letters, part of a PHANGS-JWST Focus Issue to appear in ApJ
Comment: 49 pages, 17 figures, Section 8 provides a detailed summary, accepted for publication in ApJ Letters, part of a PHANGS-JWST Focus Issue to appear in ApJ