An enhanced fraction of starbursting galaxies among high Eddington ratio
  AGNs
  We investigate the star-forming properties of 1620 X-ray selected AGN host
galaxies as a function of their specific X-ray luminosity (i.e., X-ray
luminosity per unit host stellar mass) -- a proxy of the Eddington ratio. Our
motivation is to determine whether there is any evidence of a suppression of
star-formation at high Eddington ratios, which may hint toward "AGN feedback"
effects. Star-formation rates (SFRs) are derived from fits to Herschel-measured
far-infrared spectral energy distributions, taking into account any
contamination from the AGN. Herschel-undetected AGNs are included via stacking
analyses to provide average SFRs in bins of redshift and specific X-ray
luminosity (spanning $0.01 \lesssim L_{\rm X}/M_{\ast} \lesssim 100~L_{\odot}
~M_{\odot}^{-1}$). After normalising for the effects of mass and redshift
arising from the evolving galaxy main sequence, we find that the SFRs of high
specific luminosity AGNs are slightly enhanced compared to their lower specific
luminosity counterparts. This suggests that the SFR distribution of AGN hosts
changes with specific X-ray luminosity, a result reinforced by our finding of a
significantly higher fraction of starbursting hosts among high specific
luminosity AGNs compared to that of the general star-forming galaxy population
(i.e., 8-10 per cent vs. 3 per cent). Contrary to our original motivation, our
findings suggest that high specific luminosity AGNs are more likely to reside
in galaxies with enhanced levels of star-formation.
