STELLAR AND BLACK HOLE MASS DENSITIES AS EMPIRICAL TRACERS OF CO-EVOLUTION SHOW LOCK-STEP GROWTH SINCE Z ∼ 3

Abstract

At redshifts beyond z similar to 1, measuring the black hole (BH) galaxy relations proves to be a difficult task. The bright light of the active galactic nuclei aggravates the deconvolution of BH and galaxy properties. However, high-redshift data on these relations are vital to understand the ways in which galaxies and BHs co-evolve and the ways in which they do not. In this work we use BH and stellar mass densities (BHMDs and SMDs) to constrain the possible co-evolution of BHs with their host galaxies since z similar to 5. The BHMDs are calculated from quasar luminosity functions using the Soltan argument, while we use integrals over stellar mass functions or the star-formation rate density to obtain values for the SMD. We find that both quantities grow in lock-step below redshifts of z similar to 3 with a non-evolving BHMD to SMD ratio. A fit to the data assuming a power-law relation between the BHMD and the SMD yields exponents around unity (1.0-1.5). Up to z similar to 5 the BHMD to SMD ratio does not show a strong evolution given the larger uncertainty in the completeness of high-redshift data sets. Our results, always applying the same analysis technique, seem to be consistent across all adopted data sets.