The star formation rates of active galactic nuclei host galaxies

TL;DR

This study compares star formation rates in various active galactic nuclei host galaxies using neural network predictions, revealing differences linked to AGN types and their triggering mechanisms such as galaxy mergers.

Contribution

It introduces a novel application of neural networks to estimate infrared luminosities and analyze SFR differences across AGN classes, highlighting the role of galaxy mergers in AGN activity.

Findings

Optically selected AGN have median Delta SFR = -0.06 dex.

LERGs show even lower SFRs with median Delta SFR = -0.5 dex.

Mid-IR selected AGN exhibit SFRs enhanced by about 1.5 times.

Abstract

Using artificial neural network (ANN) predictions of total infra-red luminosities (LIR), we compare the host galaxy star formation rates (SFRs) of ~21,000 optically selected active galactic nuclei (AGN), 466 low excitation radio galaxies (LERGs) and 721 mid-IR selected AGN. SFR offsets (Delta SFR) relative to a sample of star-forming `main sequence' galaxies (matched in M*, z and local environment) are computed for the AGN hosts. Optically selected AGN exhibit a wide range of Delta SFR, with a distribution skewed to low SFRs and a median Delta SFR = -0.06 dex. The LERGs have SFRs that are shifted to even lower values with a median Delta SFR = -0.5 dex. In contrast, mid-IR selected AGN have, on average, SFRs enhanced by a factor ~1.5. We interpret the different distributions of Delta SFR amongst the different AGN classes in the context of the relative contribution of triggering by galaxy mergers. Whereas the LERGs are predominantly fuelled through low accretion rate secular processes which are not accompanied by enhancements in SFR, mergers, which can simultaneously boost SFRs, most frequently lead to powerful, obscured AGN.