The Cosmic Evolution of Fermi BL Lacertae Objects

M. Ajello; R.~W. Romani; D. Gasparrini; M.~S. Shaw; J. Bolmer; G. Cotter; J. Finke; J. Greiner; S.~E. Healey; O. King; W. Max-Moerbeck; P.~F. Michelson; W.~J. Potter; A. Rau; A.~C.~S. Readhead; J.~L. Richards; P. Schady

doi:10.1088/0004-637X/780/1/73

The Cosmic Evolution of Fermi BL Lacertae Objects

M. Ajello, R.~W. Romani, D. Gasparrini, M.~S. Shaw, J. Bolmer, G. Cotter, J. Finke, J. Greiner, S.~E. Healey, O. King, W. Max-Moerbeck, P.~F. Michelson, W.~J. Potter, A. Rau, A.~C.~S. Readhead, J.~L. Richards, P. Schady

Department of Physics

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Abstract

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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of , and that most are seen within 10° of the jet axis.

Original language	English
Pages (from-to)	73
Number of pages	1
Journal	Astrophysical Journal
Volume	780
Issue number	1
DOIs	https://doi.org/10.1088/0004-637X/780/1/73
Publication status	Published - 13 Dec 2013

Keywords

cosmology: observations, diffuse radiation, galaxies: active, galaxies: jets, gamma rays: diffuse background, surveys, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena

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10.1088/0004-637X/780/1/73

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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. (2013). The Cosmic Evolution of Fermi BL Lacertae Objects. Astrophysical Journal, 780(1), 73. https://doi.org/10.1088/0004-637X/780/1/73

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abstract = "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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of , and that most are seen within 10° of the jet axis.",

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AU - Ajello, M.

AU - Romani, R.~W.

AU - Gasparrini, D.

AU - Shaw, M.~S.

AU - Bolmer, J.

AU - Cotter, G.

AU - Finke, J.

AU - Greiner, J.

AU - Healey, S.~E.

AU - King, O.

AU - Max-Moerbeck, W.

AU - Michelson, P.~F.

AU - Potter, W.~J.

AU - Rau, A.

AU - Readhead, A.~C.~S.

AU - Richards, J.~L.

AU - Schady, P.

PY - 2013/12/13

Y1 - 2013/12/13

N2 - 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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of , and that most are seen within 10° of the jet axis.

AB - 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 beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of , and that most are seen within 10° of the jet axis.

KW - cosmology: observations, diffuse radiation, galaxies: active, galaxies: jets, gamma rays: diffuse background, surveys, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena

U2 - 10.1088/0004-637X/780/1/73

DO - 10.1088/0004-637X/780/1/73

M3 - Article

SN - 0004-637X

VL - 780

SP - 73

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

ER -

The Cosmic Evolution of Fermi BL Lacertae Objects

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