Observational evidence that positive and negative AGN feedback depends on galaxy mass and jet power

Abstract

Several studies support the existence of a link between the AGN and star formation activity. Radio jets have been argued to be an ideal mechanism for direct interaction between the AGN and the host galaxy. A drawback of previous surveys of AGN is that they are fundamentally limited by the degeneracy between redshift and luminosity in flux-density limited samples. To overcome this limitation, we present far-infrared Herschel observations of 74 radio-loud quasars (RLQs), 72 radio-quiet quasars (RQQs) and 27 radio galaxies (RGs), selected at 0.9<z<1.1 which span over two decades in optical luminosity. By decoupling luminosity from evolutionary effects, we investigate how the star formation rate (SFR) depends on AGN luminosity, radio-loudness and orientation. We find that: 1) the SFR shows a weak correlation with the bolometric luminosity for all AGN sub-samples, 2) the RLQs show a SFR excess of about a factor of 1.4 compared to the RQQs, matched in terms of black hole mass and bolometric luminosity, suggesting that either positive radio-jet feedback or radio AGN triggering are linked to star-formation triggering and 3) RGs have lower SFRs by a factor of 2.5 than the RLQ sub-sample with the same BH mass and bolometric luminosity. We suggest that there is some jet power threshold at which radio-jet feedback switches from enhancing star formation (by compressing gas) to suppressing it (by ejecting gas). This threshold depends on both galaxy mass and jet power.