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arXiv · 2608.16802

JWST Whirlpool Galaxy Treasury: Mid-Infrared Emission in M51 and its Relation to Gas Column and Star Formation

Mansi Padave·Karin M. Sandstrom·Daniel A. Dale·Adam K. Leroy·Eric W. Koch·Tony D. Weinbeck·Angela Adamo·Jessica Sutter·Lindsey Hands·Torsten Böker·Martha L. Boyer·Ryan Chown·Bruce T. Draine·Ilse de Looze·Brandt A. L. Gaches·Simon C. O. Glover·Dario Colombo·Robert C. Kennicutt Jr.·Hannah Koziol·Ralf S. Klessen·Sean T. Linden·Desika Narayanan·Alex Pedrini·Julia Roman-Duval·Eva Schinnerer·J. D. T. Smith·Sophia K. Stuber·Fabian Walter
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Abstract

Using JWST/MIRI imaging of M51 in eight broadband filters, we investigate correlations of mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs) and dust continuum with molecular, atomic, and ionized gas traced by CO(1-0), HI, and Pa-alpha, respectively. In molecular gas-dominated regions, PAH-dominated filters (F560W, F770W, F1130W, F1280W) exhibit near-linear correlations with CO(1-0) at 40 pc scale, indicating that PAHs are well-mixed with gas and experience relatively constant radiation field intensities. The F1500W, F1800W, and F2100W dust continuum-dominated filters show shallower slopes with CO(1-0), reflecting contributions from star-forming regions with high radiation field intensities. This is reinforced by the near-linear scaling between F2100W and Pa-alpha. PAH-dominated bands do not show this linear trend with Pa-alpha, likely due to their destruction in ionized regions. F1000W behaves similarly to PAH bands in its correlations with CO(1-0) and Pa-alpha. Modeling mid-infrared emission with an empirical decomposition into gas- and star-formation-associated components shows that PAH-dominated filters receive comparable contributions from both, while the relative contribution associated with the Pa-alpha template increases toward longer wavelengths, reaching $\sim$75% in F2100W. These results demonstrate that mid-infrared simultaneously traces the gas column and star formation, but with a systematic wavelength-dependent shift in what drives the correlations: PAHs being more gas-tracing and dust-continuum reflecting star formation. Lastly, considering both HI and H$_2$ at 440 pc resolution, we find a tight, linear relation between $\Sigma_{HI+H_2}$ and PAH-dominated filters. Although most of our coverage is in H$_2$-dominated regions, we note similar observations with HI, suggesting that PAHs are also well-mixed with atomic gas.

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Mansi Padave, Karin M. Sandstrom, Daniel A. Dale, Adam K. Leroy, Eric W. Koch, Tony D. Weinbeck, Angela Adamo, Jessica Sutter, Lindsey Hands, Torsten Böker, Martha L. Boyer, Ryan Chown, Bruce T. Draine, Ilse de Looze, Brandt A. L. Gaches, Simon C. O. Glover, Dario Colombo, Robert C. Kennicutt Jr., Hannah Koziol, Ralf S. Klessen, Sean T. Linden, Desika Narayanan, Alex Pedrini, Julia Roman-Duval, Eva Schinnerer, J. D. T. Smith, Sophia K. Stuber, Fabian Walter. 2026-08-17. JWST Whirlpool Galaxy Treasury: Mid-Infrared Emission in M51 and its Relation to Gas Column and Star Formation. https://arxiv.org/abs/2608.16802

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