Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei

TL;DR

This study reports the first detection of methanimine megamasers in galaxy nuclei, revealing their association with nuclear activity in compact obscured galaxy cores and their potential as probes of nuclear processes.

Contribution

It is the first to identify methanimine megamasers in galaxy nuclei and links their emission to nuclear activity within compact obscured nuclei.

Findings

Methanimine megamasers detected in 6 out of 7 galaxies.

Methanimine luminosities exceed 1 L$_{ ext{sun}}$, classifying them as megamasers.

Strong correlation between methanimine and OH megamaser luminosities.

Abstract

We present the first search for the 5.29 GHz methanimine($\rm{CH}_2\rm{NH}$) $1_{10}-1_{11}$ transition toward a sample of galaxy nuclei. We target seven galaxies that host Compact Obscured Nuclei (CONs) with the Karl G. Jansky Very Large Array. These galaxies are characterized by Compton-thick cores. $\rm{CH}_2\rm{NH}$ emission is detected toward six CONs. The brightness temperatures measured toward Arp220 indicate maser emission. Isotropic luminosities of the $\rm{CH}_2\rm{NH}$ transition, from all sources where it is detected, exceed 1 L$_{\odot}$ and thus may be considered megamasers. We also detect formaldehyde ($\rm{H}_2\rm{CO}$) emission toward three CONs. The isotropic $\rm{CH}_2\rm{NH}$ luminosities are weakly correlated with the infrared luminosity of the host galaxy and strongly correlated with OH megamaser luminosities from the same galaxies. Non-LTE radiative transfer models suggest that the maser is pumped by the intense mm/submm radiation field of the CONs. Our study suggests that $\rm{CH}_2\rm{NH}$ megamasers are linked to the nuclear processes within 100 pc of the Compton Thick nucleus within CONs.