Disclosing the Radio Loudness Distribution Dichotomy in Quasars: An Unbiased Monte Carlo Approach Applied to the SDSS-FIRST Quasar Sample

Baloković, M. and Smolčić, Vernesa and Ivezić, Ž. and Zamorani, G. and Schinnerer, E. and Kelly, B. C. (2012) Disclosing the Radio Loudness Distribution Dichotomy in Quasars: An Unbiased Monte Carlo Approach Applied to the SDSS-FIRST Quasar Sample. Astrophysical Journal, 759 (1). pp. 30-43. ISSN 0004-637X

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Abstract

We investigate the dichotomy in the radio loudness distribution of quasars by modeling their radio emission and various selection effects using a Monte Carlo approach. The existence of two physically distinct quasar populations, the radio-loud and radio-quiet quasars, is controversial and over the last decade a bimodal distribution of radio loudness of quasars has been both affirmed and disputed. We model the quasar radio luminosity distribution with simple unimodal and bimodal distribution functions. The resulting simulated samples are compared to a fiducial sample of 8300 quasars drawn from the SDSS DR7 Quasar Catalog and combined with radio observations from the FIRST survey. Our results indicate that the SDSS-FIRST sample is best described by a radio loudness distribution which consists of two components, with (12 ± 1)% of sources in the radio-loud component. On the other hand, the evidence for a local minimum in the loudness distribution (bimodality) is not strong and we find that previous claims for its existence were probably affected by the incompleteness of the FIRST survey close to its faint limit. We also investigate the redshift and luminosity dependence of the radio loudness distribution and find tentative evidence that at high redshift radio-loud quasars were rarer, on average louder, and exhibited a smaller range in radio loudness. In agreement with other recent work, we conclude that the SDSS-FIRST sample strongly suggests that the radio loudness distribution of quasars is not a universal function, and that more complex models than presented here are needed to fully explain available observations.

Item Type: Article
Keywords: galaxies: active; galaxies: evolution; galaxies: high-redshift; methods: statistical; quasars: general; radio continuum: galaxies
Date: 2012
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © 2012 American Astronomical Society. Received 2011 January 18; accepted 2012 August 24; published 2012 October 15.
Divisions: Faculty of Science > Department of Physics
Publisher: IOP Publishing
Depositing User: Vernesa Smolčić
Date Deposited: 20 Apr 2015 08:05
Last Modified: 19 Apr 2016 13:40
URI: http://digre.pmf.unizg.hr/id/eprint/3836

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