The star formation rates of active galactic nuclei host galaxies
  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.
