The AGNIFS survey: distribution and excitation of the hot molecular and ionised gas in the inner kpc of nearby AGN hosts

TL;DR

This study maps hot molecular and ionised gas in the inner kiloparsec of 36 nearby active galaxies, revealing excitation mechanisms, spatial distributions, and differences between AGN types, with implications for understanding AGN fueling.

Contribution

First comprehensive spatially-resolved analysis of H$_2$ and Br$\gamma$ emissions in a large sample of nearby AGN, detailing excitation processes and morphological differences.

Findings

H$_2$ emission is less concentrated than Br$\gamma$ emission.

Thermal processes dominate H$_2$ excitation, with shocks and fluorescence identified.

Gas masses are sufficient to fuel AGN for 10$^5$-10$^8$ years.

Abstract

We use the Gemini NIFS instrument to map the H$_2 2.1218\mu$m and Br$\gamma$ flux distributions in the inner 0.04-2 kpc of a sample of 36 nearby active galaxies ($0.001\lesssim z\lesssim0.056$) at spatial resolutions from 4 to 250 pc. We find extended emission in 34 galaxies. In $\sim$55% of them, the emission in both lines is most extended along the galaxy major axis, while in the other 45% the extent follows a distinct orientation. The emission of H$_2$ is less concentrated than that of Br$\gamma$, presenting a radius that contains half of the flux 60% greater, on average. The H$_2$ emission is driven by thermal processes - X-ray heating and shocks - at most locations for all galaxies, where $0.4<H_2/Br\gamma<6$. For regions where H$_2$/Br$\gamma>6$ (seen in 40% of the galaxies), shocks are the main H$_2$ excitation mechanism, while in regions with H$_2$/Br$\gamma<0.4$ (25% of the sample) the H$_2$ emission is produced by fluorescence. The only difference we found between type 1 and type 2 AGN was in the nuclear emission-line equivalent widths, that are smaller in type 1 than in type 2 due to a larger contribution to the continuum from the hot dusty torus in the former. The gas masses in the inner 125 pc radius are in the range $10^1-10^4$ M$_\odot$ for the hot H$_2$ and $10^3-10^6$ M$_\odot$ for the ionised gas and would be enough to power the AGN in our sample for $10^5-10^8$ yr at their current accretion rates.