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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. 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. Here, 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 lesssim 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. Additionally, we 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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of $$\gamma =6.1^{+1.1}_{-0.8}$$, and that most are seen within 10° of the jet axis.
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [4] ;  [5] ;  [6] ;  [7] ;  [2] ;  [8] ;  [8] ;  [2] ;  [5] ;  [7] ;  [8] ;  [8] ;  [7]
  1. Univ. of California, Berkeley, CA (United States). Space Sciences Lab.
  2. Stanford Univ., CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
  3. Agenzia Spaziale Italiana (ASI) Science Data Center, Rome (Italy); National Institute for Astrophysics-Astronomical Observatory of Rome, Rome (Italy).
  4. Technical Univ. of Munchen, Garching (Germany). Dept. of Physics
  5. Univ. of Oxford (United Kingdom). Dept. of Astrophysics
  6. Naval Research Lab. (NRL), Washington, DC (United States). Space Science Division
  7. Max Planck Inst. for Extraterrestrial Physics, Garching (Germany)
  8. California Inst. of Technology (CalTech), Pasadena, CA (United States). Dept. of Astronomy
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 780; Journal Issue: 1; Journal ID: ISSN 0004-637X
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Contributing Orgs:
Fermi LAT Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; cosmology: observations; diffuse radiation; galaxies: active; galaxies: jets; gamma rays: diffuse background; surveys
OSTI Identifier:
1356540

Ajello, M., Romani, R. W., Gasparrini, D., Shaw, M. S., Bolmer, J., Cotter, G., Finke, J., Greiner, J., Healey, S. E., King, O., Max-Moerbeck, W., Michelson, P. F., Potter, W. J., Rau, A., Readhead, A. C. S., Richards, J. L., and Schady, P.. The cosmic evolution of Fermi BL lacertae objects. United States: N. p., Web. doi:10.1088/0004-637X/780/1/73.
Ajello, M., Romani, R. W., Gasparrini, D., Shaw, M. S., Bolmer, J., Cotter, G., Finke, J., Greiner, J., Healey, S. E., King, O., Max-Moerbeck, W., Michelson, P. F., Potter, W. J., Rau, A., Readhead, A. C. S., Richards, J. L., & Schady, P.. The cosmic evolution of Fermi BL lacertae objects. United States. doi:10.1088/0004-637X/780/1/73.
Ajello, M., Romani, R. W., Gasparrini, D., Shaw, M. S., Bolmer, J., Cotter, G., Finke, J., Greiner, J., Healey, S. E., King, O., Max-Moerbeck, W., Michelson, P. F., Potter, W. J., Rau, A., Readhead, A. C. S., Richards, J. L., and Schady, P.. 2013. "The cosmic evolution of Fermi BL lacertae objects". United States. doi:10.1088/0004-637X/780/1/73. https://www.osti.gov/servlets/purl/1356540.
@article{osti_1356540,
title = {The cosmic evolution of Fermi BL lacertae objects},
author = {Ajello, M. and Romani, R. W. and Gasparrini, D. and Shaw, M. S. and Bolmer, J. and Cotter, G. and Finke, J. and Greiner, J. and Healey, S. E. and King, O. and Max-Moerbeck, W. and Michelson, P. F. and Potter, W. J. and Rau, A. and Readhead, A. C. S. and Richards, J. L. and Schady, P.},
abstractNote = {Fermi has provided the largest sample of γ-ray-selected blazars to date. 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. Here, 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 lesssim 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. Additionally, we 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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of $\gamma =6.1^{+1.1}_{-0.8}$, and that most are seen within 10° of the jet axis.},
doi = {10.1088/0004-637X/780/1/73},
journal = {Astrophysical Journal},
number = 1,
volume = 780,
place = {United States},
year = {2013},
month = {12}
}