MIR spectra of AGNs heating molecular gas

We determine if and how accreting SMBHs at the centre of galaxies - known as active galactic nuclei (AGNs) - heat and ionize their host galaxies' dust and molecular gas. We use four MIR diagnostics to estimate the contribution of the AGN to the total MIR emission.

We refer to galaxies whose AGNs contribute more than 50 per cent of the total MIR emission as AGN dominated. We compare the relative strengths of polycyclic aromatic hydrocarbon (PAH) emission features and find that PAH grains in AGN-dominated sources have a wider range of sizes and fractional ionizations than PAH grains in non-AGN-dominated sources. We measure rotational transitions of H_2_ and estimate H_2_ excitation temperatures and masses for individual targets, H_2_ excitation temperatures for spectra stacked by their AGN contribution to the MIR, and the H_2_ excitation temperature distributions via a hierarchical Bayesian model.