The Gamma-Ray Luminosity Function of Flat-spectrum Radio Quasars

We have utilized the largest sample of gamma-ray-selected Fermi flat-spectrum radio quasars (FSRQs) ever used (519 sources) to construct the luminosity function and its evolution through cosmic history. In addition to spanning large redshift (0 < z ≲ 4) and luminosity ranges (2.9 × 10$^{43}$ erg s$^{−1}$–7.3 × 10$^{48}$ erg s$^{−1}$), this sample also has a robust calculation of the detection efficiency associated with its observation, making its selection effects and biases well understood. We confirm that the local luminosity function is best explained by a double power law. The evolution of the luminosity function of FSRQs follows a luminosity-dependent density evolution. FSRQs experience positive evolution, with their space density growing with increasing redshift up to a maximum redshift, after which the numbers decrease. This peak in redshift occurs at larger redshifts for higher-luminosity sources and at lower redshifts for lower-luminosity sources. We find an unexpected similarity between the luminosity function of FSRQs and that of BL Lacertae objects (BL Lacs) at intermediate luminosity. This could be a sign of a strong genetic link between the two blazar subclasses or of BL Lac samples being contaminated by large amounts of FSRQs with their jets nearly perfectly aligned with our line of sight.