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Title: The cosmic evolution of Fermi BL Lacertae objects

Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by Fermi during its first year of operation. We obtained redshift constraints for 206 out of the 211 BL Lac objects in our sample, making it the largest and most complete sample of BL Lac objects available in the literature. We use this sample to determine the luminosity function of BL Lac objects and its evolution with cosmic time. We find that for most BL Lac classes the evolution is positive, with a space density peaking at modest redshift (z ≈ 1.2). Low-luminosity, high-synchrotron-peaked (HSP) BL Lac objects are an exception, showing strong negative evolution, with number density increasing for z ≲ 0.5. Since this rise corresponds to a drop-off in the density of flat-spectrum radio quasars (FSRQs), a possible interpretation is that these HSPs represent an accretion-starved end state of an earlier merger-driven gas-rich phase. We additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the so-called 'blazar sequence'. Finally, by estimating the beamingmore » corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of γ=6.1{sub −0.8}{sup +1.1}, and that most are seen within 10° of the jet axis.« less
Authors:
 [1] ; ; ; ;  [2] ;  [3] ;  [4] ; ;  [5] ;  [6] ; ; ;  [7] ; ; ; ;  [8]
  1. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
  2. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
  3. Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati, Roma (Italy)
  4. Physik Dept., Technische Universität München, James-Franck-Str., 85748 Garching (Germany)
  5. Department of Astrophysics, University of Oxford, Oxford OX1 3RH (United Kingdom)
  6. Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
  7. Max-Planck Institut für extraterrestrische Physik, D-85748 Garching (Germany)
  8. Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22348288
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BL LACERTAE OBJECTS; CORRECTIONS; CORRELATIONS; COSMIC GAMMA SOURCES; COSMOLOGY; DENSITY; EVOLUTION; EXCEPTIONS; GALAXIES; LUMINOSITY; PHOTONS; QUASARS; RED SHIFT; SPACE; SPECTRA