SMBH accretion properties of radio-selected AGN out to z~4

I will discuss the most recent results about Active Galactic Nuclei (AGN) accretion in radio-selected AGN, which are key laboratories for studying supermassive black hole (SMBH) activity, and its role in quenching galaxy star formation. The questions we tried to address is: "Does SMBH accretion in radio AGN change with radio power and cosmic time?"
We explored a large (>1200) and complete sample of radio AGN from the VLA-COSMOS 3 GHz Large Project (PI: Smolcic) spanning four orders of magnitude in radio luminosity (Lr) across a wide redshift range (0.6 < z < 5). We measured the average SMBH accretion rate (BHAR) of radio AGN by stacking the latest Chandra COSMOS+Legacy images, in bins of both Lr and redshift. While the average BHAR does not show any significant trend with Lr, at any redshift, we do find a significant increase of BHAR with redshift, at fixed Lr. Interestingly, we observe a similar redshift in the fraction of blue (star-forming) radio AGN hosts, implying a possible link between BHAR and star-forming (SF) content within the host. However, the same fraction of SF hosts is also shown by a control sample of non-radio-AGN, as if the presence of a radio AGN did not affect the overall SF content of the host galaxy. Our results imply that: (i) the high-redshift Universe facilitates active SMBH activity, and (2) radio AGN feedback might not be the primary culprit for quenching galaxy star formation.