Abstract
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.
Users
Please
log in to take part in the discussion (add own reviews or comments).