JWST Observations of Starbursts: Relations between PAH features and CO clouds in the starburst galaxy M 82

¹ Departamento de Astronomía, Universidad de Concepción, Barrio Universitario, Concepción, Chile
² Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
⁵ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
⁶ Department of Astronomy, The Ohio State University, Columbus, OH 43210, USA
⁷ IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁸ Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
⁹ Sterrenkundig Observatorium, Ghent University, Krijgslaan 281 – S9, B9000 Ghent, Belgium
¹⁰ Departamento Física Teórica y del Cosmos, Universidad de Granada, E-18071 Granada, Spain
¹¹ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, E-18071 Granada, Spain
¹² European Space Agency, c/o STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹⁴ National Radio Astronomy Observatory, PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA
¹⁵ New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, USA
¹⁶ IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁷ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
¹⁸ Millenium Nucleus for Galaxies, MINGAL
¹⁹ Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606, USA
²⁰ Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
²¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

^⋆ Corresponding author; fumitaka.nakamura@nao.ac.jp

Received: 24 January 2025
Accepted: 24 February 2025

Abstract

We present a study of new 7.7–11.3 μm data obtained with the James Webb Space Telescope Mid-InfraRed Instrument in the starburst galaxy M 82. In particular, we focus on the dependency of the integrated CO(1–0) line intensity on the MIRI-F770W and MIRI-F1130W filter intensities to investigate the correlation between H₂ content and the 7.7 and 11.3 μm features from polycyclic aromatic hydrocarbons (PAH) in M 82’s outflows. To perform our analysis, we identify CO clouds using the archival ¹²CO(J = 1 − 0) NOEMA moment 0 map within 2 kpc from the center of M 82, with sizes ranging between ∼21 and 270 pc; then, we compute the CO-to-PAH relations for the 306 validated CO clouds. On average, the power-law slopes for the two relations in M 82 are lower than what is seen in local main-sequence spirals. In addition, there is a moderate correlation between I_{CO(1 − 0)} − I_7.7 μm/I_11.3 μm for some of the CO cloud groups analyzed in this work. Our results suggest that the extreme conditions in M 82 translate into CO not tracing the full budget of molecular gas in smaller clouds, perhaps as a consequence of photoionization and/or emission suppression of CO molecules due to hard radiation fields from the central starburst.