  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.
