Molecular Gas Heating and Modified Dust Properties in Active Galaxies: Growing Black Holes or Tidal Shocks?

Abstract

We investigate if and how growing super-massive black holes (SMBH) known as Active Galactic Nuclei (AGN) and gravitational interactions affect the warm molecular gas and dust of galaxies. Our analysis focuses on the morphologies and warm ISM properties of 630 galaxies at z < 0.1. We use grizy images from the Pan-STARRS survey to classify the galaxies into mergers, early mergers, and non-mergers. We use MIR spectroscopic measurements of emission from rotational H 2 transitions, dust and PAH features, and silicate emission or absorption lines at 9.7 µm to study how gravitational interactions impact the warm ISM in AGN and non-AGN hosts.We find that in AGN-hosts, the ISM is warmer, the ratios of H 2 to PAHs are larger, the PAH emission line ratios and silicate strengths have a wider range of values than in non-AGN hosts. We find some statistical differences between the H 2 emission of mergers and non-mergers, but those differences are less statistically significant than those between AGN and non-AGN hosts.Our results do not establish a relation between the rate of BH growth and the warm ISM but point to highly statistically significant differences between AGN hosts and non-AGN hosts, differences that are not present with the same statistical significance between mergers and non-mergers. We speculate that the combination of triggering mechanisms, AGN orientations, and evolutionary stages that allow AGN to be classified as such in the MIR indicate that those AGN are energetically coupled on kpc scales to their host galaxies's warm ISM. Future optical and IR, spatially resolved spectroscopic studies are best suited to characterize this connection.