Mid-J CO Emission in Nearby Seyfert Galaxies

TL;DR

This paper presents the first complete sub-millimeter spectra of nearby active galaxies, analyzing CO emission to understand the heating mechanisms of warm molecular gas in Seyfert galaxies.

Contribution

It provides the first detailed CO spectral line energy distribution for Seyfert galaxies and compares observational data with PDR and XDR models to identify gas heating sources.

Findings

CO lines probe warm molecular gas heated by AGN or star formation.

Radiative transfer modeling estimates physical conditions of molecular gas.

Comparison with PDR/XDR models suggests dominant heating mechanisms.

Abstract

We study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup = 4 to 12) is the most prominent spectral feature in this range. These CO lines probe warm molecular gas that can be heated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleus or in young star-forming regions. In these proceedings we investigate the physical origin of the CO emission using the averaged CO spectral line energy distribution (SLED) of six Seyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneous medium to estimate the molecular gas conditions. We also compare this CO SLED with the predictions of photon and X-ray dominated region (PDR and XDR) models.