Herschel far-infrared photometry of the Swift Burst Alert Telescope active galactic nuclei sample of the local universe - III. Global star-forming properties and the lack of a connection to nuclear activity

TL;DR

This study analyzes the star-forming properties of local AGN host galaxies using Herschel and WISE data, revealing no strong link between nuclear activity and star formation, and providing IR-based AGN diagnostics.

Contribution

It offers a comprehensive SED decomposition of over 300 local AGN, quantifies their dust and star formation properties, and explores the IR signatures of AGN activity, advancing understanding of galaxy evolution.

Findings

AGN hosts have higher dust masses, temperatures, and SFRs than non-AGN galaxies.

Approximately 30% of the sample's 70 μm emission is significantly influenced by AGN.

The SFR-AGN luminosity relationship shows a shallow slope with large scatter and no high-luminosity upturn.

Abstract

We combine the Herschel Space Observatory PACS and SPIRE photometry with archival WISE photometry to construct the spectral energy distributions (SED) for over 300 local ($z < 0.05$), ultra-hard X-ray (14 - 195 keV) selected active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) 58 month catalogue. Using a simple analytical model that combines an exponentially cut-off powerlaw with a single temperature modified blackbody, we decompose the SEDs into a host-galaxy and AGN component. We calculate dust masses, dust temperatures, and star-formation rates (SFR) for our entire sample and compare them to a stellar mass-matched sample of local non-AGN galaxies. We find AGN host galaxies have systematically higher dust masses, dust temperatures, and SFRs due to the higher prevalence of late-type galaxies to host an AGN, in agreement with previous studies of the Swift/BAT AGN. We provide a scaling to convert X-ray luminosities into 8 - 1000 $\mu$m AGN luminosities, as well as determine the best mid-to-far IR colors for identifying AGN dominated galaxies in the IR regime. We find that for nearly 30 per cent of our sample, the 70 $\mu$m emission contains a significant contribution from the AGN ($> 0.5$), especially at higher luminosities ($L_{14-195\,\rm{keV}} > 10^{42.5}$ ergs s$^{-1}$). Finally, we measure the local SFR-AGN luminosity relationship, finding a slope of 0.18, large scatter (0.37 dex), and no evidence for an upturn at high AGN luminosity. We conclude with a discussion on the implications of our results within the context of galaxy evolution with and without AGN feedback.