Mid-Infrared Colors Vary with Galactic Environment: Contrasting Star-Forming Disks, Young Centers, and Quiescent Star-Formation Deserts
Debosmita Pathak, Karin M. Sandstrom, Adam K. Leroy, Ryan Chown, Daniel A. Dale, Hannah B. Koziol, Mansi Padave, Jessica Sutter, Thomas G. Williams, Dalya Baron, Alberto D. Bolatto, Mederic Boquien, Oleg V. Egorov, Eric Emsellem, Simon C. O. Glover, Ralf S. Klessen, Eva Schinnerer, Todd A. Thompson, Francesco Belfiore, Frank Bigiel, Enrico Congiu, Ivan Gerasimov, Jay Gonzalez Lobos, Annie Hughes, Laura A. Lopez, Justus Neumann, Elias K. Oakes, Hsi-An Pan, Erik Rosolowsky, Sumit K. Sarbadhicary
astro-ph.GA
Submitted: 2026-08-24
Updated: 2026-08-25
Comments: 24 pages, 16 figures, 3 tables; accepted for publication in ApJ
Code: https://github.com/emsellem/pymusepipe
License: http://creativecommons.org/licenses/by/4.0/
The gist: We present 50 - 100, pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the
Terminology
Abstract
We present 50 - 100, pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity (U) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band-ratios remain fairly constant in the diffuse ISM of star-forming disks. However, they show stark variations in extreme environments: highly star-forming central molecular zones (CMZs) and star-formation deserts/quiescent bulges. In CMZs, PAH-to-continuum (3.3/21, 7.7/21, and 11.3/21, mu m) and the 10/21, mu m continuum colors are 0.2 - 0.4 dex lower than in normal disks. We attribute this to higher U based on the far-IR dust colors and the high 21, mu m / Mol, which we suggest to be a good tracer of U outside star-forming regions. Meanwhile, star-formation deserts show low 7.7, mu m PAH emission, resulting in low 7.7/21, mu m and 7.7/11.3, mu m, while all other mid-IR colors remain typical. This suggests the presence of more neutral PAHs in star-formation deserts, where low 7.7, mu m likely reflects ISM conditions similar to early-type and elliptical galaxies. All environments form part of a continuous trend in 7.7/11.3, mu m vs. specific star-formation rate.
Sources
- Polycyclic aromatic hydrocarbons destruction in star-forming regions across 42 nearby galaxies
- PDRs4All: XVIII. The evolution of the PAH ionisation and PAH size distribution across the Orion Bar
- The Calibration of Short Wavelength Polycyclic Aromatic Hydrocarbon Emission as Star Formation Rate Indicators with JWST
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