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Published June 1, 2012 | Published
Journal Article Open

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


Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a complete sample of flat spectrum radio quasars (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 ~0.5-2.0 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 γ-ray FSRQs follows a luminosity-dependent density evolution similar to that of radio-quiet active galactic nuclei. Also, using data from the Swift Burst Alert Telescope we derive the average spectral energy distribution (SED) of FSRQs in the 10 keV-300 GeV band and show that there is no correlation between the luminosity at the peak of the γ-ray emission component and its peak frequency. Using this luminosity-independent SED with the derived LF allows us to predict that the contribution of FSRQs to the Fermi isotropic γ-ray background is 9.3^(+1.6)_(–1.0%)(±3% systematic uncertainty) in the 0.1-100 GeV band. Finally we determine the LF of unbeamed FSRQs, finding that FSRQs have an average Lorentz factor of γ = 11.7^(+3.3)_(– 2.2), that most are seen within 5° of the jet axis, and that they represent only ~0.1% of the parent population.

Additional Information

© 2012 American Astronomical Society. Received 2011 October 15; accepted 2012 March 28; published 2012 May 11. The authors acknowledge a very constructive report from an expert referee. M.A. acknowledges Y. Inoue and T. Venters for providing their data in electronic form and for interesting discussions about the origin of the IGRB. M.A. acknowledges support from NASA grant NNH09ZDA001N for the study of the origin of the Isotropic Gamma-ray Background. R.W.R. acknowledges NASA grant NNX08AW30G and extensive consultation with the OVRO Fermi group. The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d' Études Spatiales in France. Facilities: Fermi (LAT), Swift (BAT)

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