The hidden AGN main sequence: Evidence for a universal SMBH accretion to star formation rate ratio since z~2 producing a M_BH-M* relation
by Mullaney, J. R. and Daddi, E. and Béthermin, M. and Elbaz, D. and Juneau, S. and Pannella, M. and Sargent, M. T. and Alexander, D. M. and Hickox, R. C.
6 Pages, 3 Figures, Submitted to ApJL
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies (SFGs) at z~1 and z~2 as a function of galaxy stellar mass (M*). We find the average rate of SMBH growth taking place in SFGs follows remarkably similar trends with both M* and redshift as the average star-formation rates (SFRs) of these galaxies (i.e., dM_BH/dt ~ M*^(0.86+/-0.39) for the z~1 sample and dM_BH/dt ~ M*^(1.05+/-0.36) for the z~2 sample). It follows that the ratio of SMBH growth rate to SFR is (a) flat with respect to galaxy stellar mass (b) not evolving with redshift and (c) close to the ratio required to maintain/establish a SMBH to stellar mass ratio of ~10^(-3) as also inferred from today’s M_BH-M_Bulge relationship. We interpret this as evidence that SMBHs have, on average, grown in-step with their host galaxies since at least z~2, irrespective of host galaxy mass and AGN triggering mechanism and that the relative growth rates are more important in establishing inferred M_BH-M* relationships than the seed SMBH masses or merger history. Based on these results we speculate that it is the availability of gas reservoirs that regulates both cosmological SMBH growth and star-formation.