Dissecting the Mid-Infrared Heart of M83 with JWST

TL;DR

This study uses JWST MIRI observations to analyze the complex ionized, molecular, and dust components in M83's nucleus, revealing spatial variations and the dominance of warm molecular gas in the galaxy's central region.

Contribution

First JWST MIRI observations of M83's nucleus dissect the spatial distribution of emission features, providing new insights into the warm molecular gas and ISM interactions in the galaxy's core.

Findings

Warm H2 gas constitutes about 75% of total molecular gas mass.

Warm H2 mass estimated at approximately 68 million solar masses.

Spatial distribution of warm and cold molecular gas differs significantly.

Abstract

We present a first look at the MRS observations of the nucleus of the nearby galaxy M83, taken with MIRI onboard JWST. The observations show a rich set of emission features from the ionized gas, warm molecular gas, and dust. To begin dissecting the complex processes in this part of the galaxy, we divide the observations into four different regions. We find that the strength of the emission features varies strongly from region to region, with the south-east region displaying the weakest features tracing the dust continuum and ISM properties. Comparison between the cold molecular gas traced by the $^{12}$CO (1-0) transition with ALMA and the H$_2$ S(1) transition shows a similar spatial distribution. This is in contrast to the distribution of the much warmer H$_2$ emission from the S(7) transition found to be concentrated around the optical nucleus. We use the rotational emission lines and model the H$_2$ excitation to estimate a total molecular gas mass accounting for the warm H$_2$ component of M($>$50 K)$_{\rm H_{2}}$ = 67.90 ($\pm 5.43$)$\times$10$^{6}$ M$_{\odot}$. We compare this value to the total gas mass inferred by probing the cold H$_2$ gas through the $^{12}$CO (1-0) emission, M(CO)$_{\rm H_{2}}$ = 17.15$\times$10$^{6}$ M$_{\odot}$. We estimate that $\sim$75\% of the total molecular gas mass is contained in the warm H$_2$ component. We also identify [\ion{O}{4}] 25.89 $\mu$m and [\ion{Fe}{2}] 25.99 $\mu$m emission. We propose that the diffuse [\ion{Fe}{2}] 25.99 $\mu$m emission might be tracing shocks created during the interactions between the hot wind produced by the starburst and the much cooler ISM above the galactic plane. More detailed studies are needed to confirm such a scenario.