Dark bubbles around high-redshift radio-loud AGN

TL;DR

This paper investigates the discrepancy between the observed and expected numbers of high-redshift blazars and their parent populations, proposing that dust obscuration around quasars explains the scarcity of misaligned sources.

Contribution

It introduces a scenario where dust bubbles obscure nuclei, accounting for the missing misaligned blazars at high redshift, independent of jet orientation or Lorentz factor.

Findings

Increased number of identified blazars at z>3 demands a larger parent population.

Detected blazars have sufficient radio flux to be above survey limits.

Obscuration by dust bubbles may hide misaligned sources, explaining the discrepancy.

Abstract

At redshift larger than 3 there is a disagreement between the number of blazars (whose jet is pointing at us) and the number of expected parents (whose jet is pointing elsewhere). Now we strengthen this claim because (i) the number of blazars identified within the SDSS+FIRST survey footprint increased, demanding a more numerous parent population, and (ii) the detected blazars have a radio flux large enough to be above the FIRST flux limit even if the jet is slightly misaligned. The foreseen number of these slightly misaligned jets, in principle detectable, is much larger than the radio-detected sources in the FIRST+SDSS survey (at redshift larger than 4). This argument is independent of the presence of an isotropic radio component, such as the hot spot or the radio lobe, and does not depend on the bulk Lorentz factor Gamma. We propose a scenario that ascribes the lack of slightly misaligned sources to an over-obscuration of the nucleus by a "bubble" of dust, possibly typical of the first high-redshift quasars.