A strong redshift dependence of the broad absorption line quasar fraction

By James T. Allen, Paul Hewett, N. Maddox, Gordon Richards, V. Belokurov. 2010

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We describe the application of non-negative matrix factorization to generate compact reconstructions of quasar spectra from the Sloan Digital Sky Survey (SDSS), with particular reference to broad absorption line quasars (BALQSOs). BAL properties are measured for Si IV λ1400, C IV λ1550, Al III λ1860 and Mg II λ2800, resulting in a catalogue of 3547 BALQSOs. Two corrections, based on extensive testing of synthetic BALQSO spectra, are applied in order to estimate the intrinsic fraction of C IV BALQSOs. First, the probability of an observed BALQSO spectrum being identified as such by our algorithm is calculated as a function of redshift, signal-to-noise ratio and BAL properties. Secondly, the different completenesses of the SDSS target selection algorithm for BALQSOs and non-BAL quasars are quantified. Combining the detection probabilities with an intrinsic E(B - V) distribution capable of reproducing the observed increase in mean E(B - V) with increasing redshift, the intrinsic C IV BALQSO fraction is 41 ± 5 per cent. Our analysis of the selection effects allows us to measure the dependence of the intrinsic C IV BALQSO fraction on luminosity and redshift. We find a factor of 3.5 ± 0.4 decrease in the intrinsic fraction from the highest redshifts, z ≃ 4.0, down to z ≃ 2.0. The redshift dependence implies that an orientation effect alone is not sufficient to explain the presence of BAL troughs in some but not all quasar spectra. Our results are consistent with the intrinsic BALQSO fraction having no strong luminosity dependence, although with 3 σ limits on the rate of change of the intrinsic fraction with luminosity of -6.9 and 7.0 per cent dex -1 we are unable to rule out such a dependence.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/62ffa55a48e937229fb8b4797624aacf4d4432a9

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Citations in the corpus

The Sloan Digital Sky Survey quasar catalog: ninth data release (2012, methodology): “We checked the 131 objects for which we measured BI > 0 but Allen et al. (2011) found BI= 0 individually.”
UNIFICATION OF LUMINOUS TYPE 1 QUASARS THROUGH C iv EMISSION (2010, methodology): “Finally, we have removed all known BALQSOs as cataloged by Allen et al. (2011).”
Observational evidence of quasar feedback quenching star formation at high redshift (2011, background): “Evidence of outflows in luminous quasars has been detected up to very high redshift (e.g. Allen et al., 2011; Maiolino etal., 2004; Alexander et al., 2010).”
What drives the growth of black holes (2011, background): “…found for broad absorption line (BAL) quasars, which are believed to represent the ≈ 20–40% of quasars (with evidence for a redshift dependence; e.g., Allen et al. 2011) for which the nuclear continuum is viewed through the outflow (there is evidence that maybe all quasars host energetic winds;…”
The Sloan Digital Sky Survey Quasar Catalog: Fourteenth data release (2017, methodology): “The BI distribution from Gibson et al. (2009) exhibits a slight excess of low-BI values (log BICIV < 2) compared to Allen et al. (2011) and this work.”
X-shooter reveals powerful outflows in z ∼ 1.5 X-ray selected obscured quasi-stellar objects (2014, result): “Recent works also suggest that ∼40% of IR selected and SDSS QSOs are BAL QSOs, pointing towards the fact that they are quite common (Dai et al. 2008; Allen et al. 2011) and that the outflow and unobscured phases may be of comparable length, in agreement with the Hopkins scenario (see also Glikman…”
The Sloan Digital Sky Survey Quasar Catalog: Twelfth data release (2016, methodology): “The BI distribution from Gibson et al. (2009) exhibits an excess of low-BI values compared to Allen et al. (2011) and this work.”
A refined measurement of the mean transmitted flux in the Lyα forest over 2 < z < 5 using composite quasar spectra (2012, methodology): “For quasars present in the SDSS DR6 release, BAL quasars were defined using the classifications of Allen et al. (2011), while the small fraction of quasars present only in DR7 were classified via visual inspection.”