The Luminosity Function of Fermi-detected Flat-Spectrum Radio Quasars

TL;DR

This paper analyzes the luminosity function and evolution of Fermi-detected flat-spectrum radio quasars, revealing their contribution to the gamma-ray background and their beaming properties.

Contribution

It provides the first comprehensive luminosity function and evolution model for Fermi-detected FSRQs, including their spectral energy distribution and beaming characteristics.

Findings

FSRQs peak in number density at redshift 0.5-2.0.

The luminosity function follows luminosity-dependent density evolution.

FSRQs contribute approximately 9.3% to the gamma-ray background.

Abstract

Fermi has provided the largest sample of {\gamma}-ray selected blazars to date. In this work we use a complete sample of FSRQs detected during the first year of operation to determine the luminosity function (LF) and its evolution with cosmic time. The number density of FSRQs grows dramatically up to redshift \sim0.5-2.0 and declines thereafter. The redshift of the peak in the density is luminosity dependent, with more luminous sources peaking at earlier times; thus the LF of {\gamma}-ray FSRQs follows a luminosity-dependent density evolution similarly to that of radio-quiet AGN. Also using data from the Swift Burst Alert Telescope we derive the average spectral energy distribution of FSRQs in the 10 keV-100 GeV band and show that there is no correlation of the peak {\gamma}-ray luminosity with {\gamma}-ray peak frequency. The coupling of the SED and LF allows us to predict that the contribution of FSRQs to the Fermi isotropic {\gamma}-ray background is 9.3(+1.6/-1.0) (\pm3% systematic uncertainty) in the 0.1-100GeV band. Finally we determine the LF of unbeamed FSRQs, finding that FSRQs have an average Lorentz factor of {\gamma} = 11.7(+3.3/-2.2), that most are seen within 5\circ of the jet axis, and that they represent only ~0.1 % of the parent population.