ABSTRACT
Supermassive black holes (SMBHs) play a crucial role in the evolution of galaxies and are currently detected up to $z$ ∼ 7.5. Theories describing black hole (BH) growth are challenged by how rapidly seeds with initial mass $M_\bullet \lesssim 10^5 \, {\rm M_\odot }$, formed at $z$ ∼ 20–30, grew to $M_\bullet \sim 10^9 \, {\rm M_\odot }$ by $z$ ∼ 7. Here we study the effects of the value of the Hubble parameter, H0, on models describing the early growth of BHs. First, we note that the predicted mass of a quasar at $z$ = 6 changes by $\gt 300{{\ \rm per\ cent}}$ if the underlying Hubble parameter used in the model varies from H0 = 65 to H0 = 74 km s−1Mpc−1, a range encompassing current estimates. Employing an MCMC approach based on priors from $z$ ≳ 6.5 quasars and on H0, we study the interconnection between H0 and the parameters describing BH growth: seed mass Mi and Eddington ratio fEdd. Assuming an Eddington ratio of fEdd = 0.7, in agreement with previous estimates, we find $H_0 = 73.6^{+1.2}_{-3.3}$ km s−1Mpc−1. In a second analysis, allowing all the parameters to vary freely, we find log (Mi/M⊙) > 4.5 (at 95 per cent CL), $H_0 = 74^{+1.5}_{-1.4}$ km s−1Mpc−1 and $f_{\rm Edd}=0.77^{+0.035}_{-0.026}$ at 68 per cent CL. Our results on the typical Eddington ratio are in agreement with previous estimates. Current values of the Hubble parameter strongly favour heavy seed formation scenarios, with $M_i \gtrsim 10^4 \, {\rm M_\odot }$. In our model, with the priors on BH masses of quasars used, light seed formation scenarios are rejected at ∼3σ.
RELATION BETWEEN GLOBULAR CLUSTERS AND SUPERMASSIVE BLACK HOLES IN ELLIPTICALS AS A MANIFESTATION OF THE BLACK HOLE FUNDAMENTAL PLANE