Blazars in the early Universe
Marta Volonteri, Francesco Haardt, Gabriele Ghisellini, Roberto, Della Ceca

TL;DR
This study examines the occurrence and properties of high-redshift blazars and quasars, revealing a deficit of radio-loud quasars at z>3 and discussing implications for black hole growth and observational biases.
Contribution
It provides new constraints on the density of billion-solar-mass black holes in the early Universe and explores reasons for the observed deficit of high-redshift radio-loud quasars.
Findings
Agreement with expectations up to z~3
Serious deficit of radio-loud quasars at z>3
Possible explanations include decreased Lorentz factors and observational biases
Abstract
We investigate the relative occurrence of radio--loud and radio-quiet quasars in the first billion years of the Universe, powered by black holes heavier than one billion solar masses. We consider the sample of high-redshfit blazars detected in the hard X-ray band in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. All the black holes powering these blazars exceed a billion solar mass, with accretion luminosities close to the Eddington limit. For each blazar pointing at us, there must be hundreds of similar sources (having black holes of similar masses) pointing elsewhere. This puts constraints on the density of billion solar masses black holes at high redshift (z>4), and on the relative importance of (jetted) radio-loud vs radio-quiet sources. We compare the expected number of high redshift radio--loud sources with the high luminosity…
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