Blowing star formation away in AGN Hosts (BAH) -- II. Investigating the origin of the H2 emission excess in nearby galaxies with JWST MIRI

TL;DR

This study uses JWST MIRI observations to analyze H2 emission excess in nearby AGN host galaxies, revealing shock heating from jets and outflows as the primary cause of the excess.

Contribution

It provides new evidence linking H2 emission excess to shock heating caused by AGN-driven outflows and radio jet interactions in nearby galaxies.

Findings

H2 emission excess is mainly driven by shock-heated gas.

Radio jet interaction causes shocks in 3C 293, leading to H2 emission.

Shock heating from outflows or jets explains the H2 excess in these galaxies.

Abstract

We use James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) medium-resolution spectrometer (MRS) observations of 3C 293 (UGC 8782), CGCG 012-070 and NGC 3884 to investigate the origin of the H$_2$ emission. These three nearby Active Galactic Nucleus (AGN) hosts are known to present H$_2$ emission excess relative to star-forming galaxies, as traced by the H$_2$ S(3)/PAH$_{\rm 11.3\mu m}$ line ratio. We define the kinematically disturbed region (KDR) by the AGN and the virially dominated region (VDR) based on the H$_2$ line widths, using the $W{\rm 80}$ parameter. From the correlations between $W{\rm 80}$ and H$_2$ S(3)/PAH${\rm 11.3\mu m}$, as well as the higher H$2$ S(5)/H$2$ S(3) and [Fe II]${\rm 5.34 \mu m}$/PAH${\rm 11.3\mu m}$ ratios and flatter power-law temperature distributions observed in the KDR, we conclude that the H$_2$ emission in the KDR is primarily driven by shock-heated gas. For 3C 293, the KDR is co-spatial with the radio core, indicating that the origin of the shocks is the interaction of the radio jet with the interstellar medium, which is also responsible for the observed molecular and ionized gas outflows in this source. The other galaxies are weak radio sources; however, due to the lack of high-resolution radio images, we cannot rule out low-power jets as the origin of the shock-heated H$_2$. Our results indicate that the excess H$_2$ emission excess is associated to shock heating of the gas, generated by outflows or by the interaction of the radio jet with the ambient gas.