The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity

By Linhua Jiang, Xiaohui Fan, Željko Ivezic´, Gordon Richards, D. Schneider, M. Strauss, B. Kelly. 2006

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Using a sample of optically selected quasars from the Sloan Digital Sky Survey, we have determined the radio-loud fraction (RLF) of quasars as a function of redshift and optical luminosity. The sample contains more than 30,000 objects and spans a redshift range of 0 < z ≤ 5 and a luminosity range of -30 ≤ Mi < -22. We use both the radio-to-optical flux ratio (R parameter) and the radio luminosity to define radio-loud quasars. After breaking the correlation between redshift and luminosity due to the flux-limited nature of the sample, we find that the RLF of quasars decreases with increasing redshift and decreasing luminosity. The relation can be described in the form of log [RLF/(1 − RLF)] = b0 + bz log(1 + z) + bM(M2500 + 26), where M2500 is the absolute magnitude at rest-frame 2500 Å, and bz, bM < 0. When using R > 10 to define radio-loud quasars, we find that b0 = -0.132 ± 0.116, bz = -2.052 ± 0.261, and bM = -0.183 ± 0.025. The RLF at z = 0.5 declines from 24.3% to 5.6% as luminosity decreases from M2500 = -26 to -22, and the RLF at M2500 = -26 declines from 24.3% to 4.1% as redshift increases from 0.5 to 3, suggesting that the RLF is a strong function of both redshift and luminosity. We also examine the impact of flux-related selection effects on the RLF determination using a series of tests and find that the dependence of the RLF on redshift and luminosity is highly likely to be physical, and that the selection effects we considered are not responsible for the dependence.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/30c4c14aac7fec04e4d0f5c304aab1facb5cbc9b

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Citations in the corpus

A CATALOG OF QUASAR PROPERTIES FROM SLOAN DIGITAL SKY SURVEY DATA RELEASE 7 (2010, methodology): “FIRST radio flag:−1=not in FIRST footprint; 0=FIRST undetected; 1=core dominant; 2=lobe dominant (for details, see Jiang et al. 2007, and discussion in §2).”
THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, background): “If radio loudness correlates with redshift and/or luminosity (e.g., Jiang et al. 2007; Singal et al. 2011, 2012), an attempt to correct the N(z) distribution using radio-loud quasars would be incorrect (see also the discussion in § 3.4 of R06).”
Biases in Virial Black Hole Masses: An SDSS Perspective (2007, background): “For example, Kurk et al. (2007) and Jiang et al. (2007a) have obtained observations of both MgII and CIV in four z∼ 6 quasars.”
Reverberation Mapping of High-Luminosity Quasars: First Results (2006, background): “%) are radio loud, somewhat more than the 20% radio-loud fraction (i.e., two objects) one would expect for a quasar population of this mean redshift (2.8) and luminosity (Jiang et al. 2007).”
C IV λ1549 as an Eigenvector 1 Parameter for Active Galactic Nuclei (2007, background): “The sample should be particularly valuable for RQ versus RL comparisons because the two populations are almost equally represented while in a complete sample only 10% are found to be RL (Jiang et al. 2007; Cirasuolo et al. 2003; Sulentic et al. 2003).”
QUASAR CLUSTERING FROM SDSS DR5: DEPENDENCES ON PHYSICAL PROPERTIES (2008, background): “The FIRST-detected sample contains quasars that are generally radio-loud with typical radioloudnessR ≡ f6 cm/ f2500∼ 100 (Jiang et al. 2007).”
The 2dF-SDSS LRG and QSO Survey: the QSO luminosity function at 0.4 < z < 2.6 (2009, background): “In contrast, the radio-detected fraction (to the same radio flux limit) of optically bright QSOs is no more that 25 per cent (Jiang et al. 2007).”
UNIFICATION OF LUMINOUS TYPE 1 QUASARS THROUGH C iv EMISSION (2010, background): “As the RL population is as low as ∼5% and as high as ∼20% of the total depending on redshift and luminosity (Jiang et al. 2007), other scaling factors could be more appropriate.”
21 cm cosmology in the 21st century (2011, background): “Furthermore, the radio-loud fraction of quasars is poorly understood and may evolve at higher redshifts [195].”
A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys (2013, background): “Radio-loud AGN constitute ∼10 per cent of the AGN population, the fraction of which may vary with luminosity and redshift (e.g. Jiang et al. 2007) and are known to exhibit X-ray emission attributable to synchrotron or synchro-Compton emission from a jet (Zamorani et al. 1981).”