Blazar candidates beyond redshift 4 observed by Swift

TL;DR

This study confirms that certain high-redshift, radio-loud quasars are indeed blazars with massive black holes, providing insights into black hole formation and evolution in the early universe.

Contribution

First X-ray confirmation of blazar nature for high-redshift, radio-loud quasars with massive black holes, revealing their jet properties and formation epochs.

Findings

All three candidates are confirmed as blazars with strong, hard X-ray flux.

Black hole masses exceed 10^9 solar masses in all cases.

Evidence suggests different formation epochs for jetted and non-jetted black holes.

Abstract

We have selected SDSS J222032.50+002537.5 and SDSS J142048.01+120545.9 as best blazar candidates out of a complete sample of extremely radio-loud quasars at z>4, with highly massive black holes. We observed them and a third serendipitous candidate with similar features (PMN J2134-0419) in the X-rays with the Swift/XRT telescope, to confirm their blazar nature. We observed strong and hard X-ray fluxes (i.e. $\alpha_X<0.6$, where $F(\nu)\propto\nu^{-\alpha_X}$ in the 0.3-10keV observed energy range, ~1-40keV rest frame) in all three cases. This allowed us to classify our candidates as real blazars, being characterized by large Lorentz factors (~13) and very small viewing angles (~3deg). All three sources have black hole masses exceeding 10^9Msun and their classification provides intriguing constraints on supermassive black hole formation and evolution models. We confirm our earlier suggestion that there are different formation epochs of extremely massive black holes hosted in jetted (z~4) and non-jetted systems (z~2.5).