A correlation between star formation rate and average black hole accretion in star forming galaxies

TL;DR

This study finds a nearly linear correlation between star formation rate and average black hole accretion rate in star-forming galaxies at redshifts 0.25 to 0.8, suggesting a close link between galaxy growth and black hole activity.

Contribution

It provides the first measurement of the average black hole accretion rate as a function of star formation rate for a large sample of star-forming galaxies at intermediate redshifts.

Findings

Almost linear relation between BHAR and SFR.

BHAR increases with SFR across a wide range.

Supports a tight link between galaxy growth and black hole activity.

Abstract

We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of star formation rate (SFR) for galaxies in the redshift range 0.25<z<0.8. We study a sample of 1,767 far-IR selected star-forming galaxies in the 9 deg^2 Bo\"otes multiwavelength survey field. The SFR is estimated using 250 micron observations from the Herschel Space Observatory, for which the contribution from the AGN is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M_sun/year) and the SFR (in M_sun/year) for galaxies across a wide SFR range 0.85<log SFR<2.56 : log BHAR=(-3.72\pm0.52)+(1.05\pm0.33) log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.