The redshift distribution of BL Lacs and FSRQs

TL;DR

This paper investigates the redshift distributions of BL Lacs and FSRQs, addressing overpredictions and differences through a unified model connecting black hole accretion and jet formation over cosmic time.

Contribution

It introduces a physical constraint within the gap paradigm to explain the separate peaks and tail features in the redshift distributions of BL Lacs and FSRQs.

Findings

Separate peaks in redshift distributions for BL Lacs and FSRQs explained by the model.

Identification of a tail in the BL Lac distribution not seen in FSRQs.

Physical constraints lead to different jet powers at different cosmic times.

Abstract

Flat spectrum radio quasars (FSRQs) and BL Lacs are powerful jet producing active galactic nuclei associated with supermassive black holes accreting at high and low Eddington rates, respectively. Based on the Millennium Simulation, Gardner and Done (2014; 2018) have predicted their redshift distribution by appealing to ideas from the spin paradigm in a way that exposes a need for a deeper discussion on three interrelated issues: (1) an overprediction of BL Lacs compared to flat spectrum radio quasars; (2) a difference in FSRQ and BL Lac distributions; (3) a need for powerful but different jets at separated cosmic times. Beginning with Gardner and Done's determination of Fermi observable FSRQs based on the distribution of thermal accretion across cosmic time from the Millennium Simulation, we connect FSRQs to BL Lacs by way of the gap paradigm for black hole accretion and jet formation to address the above issues in a unified way. We identify a physical constraint in the paradigm for the numbers of BL Lacs that naturally leads to separate peaks in time for different albeit powerful jets. In addition, we both identify as puzzling and ascribe physical significance to a tail end in the BL Lac curve versus redshift that is unseen in the redshift distribution for FSRQs.