The University of Southampton
University of Southampton Institutional Repository

The intrinsic fraction of broad-absorption line quasars

The intrinsic fraction of broad-absorption line quasars
The intrinsic fraction of broad-absorption line quasars
We carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate of the intrinsic BALQSO fraction from the Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. We first show that the distribution of objects selected by the so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high BALQSO fractions that have recently been inferred from AI-based samples are therefore likely to be overestimated. We then present two new approaches to the classification problem that are designed to be more robust than the AI, but also more complete than the traditional 'balnicity index' (BI). Both approaches yield observed BALQSO fractions around 13.5 per cent, while a conservative third approach suggests an upper limit of 18.3 per cent. Finally, we discuss the selection biases that affect our observed BALQSO fraction. After correcting for these biases, we arrive at our final estimate of the intrinsic BALQSO fraction. This is fBALQSO= 0.17 ± 0.01 (stat) ± 0.03 (sys) with an upper limit of fBALQSO? 0.23 . We conclude by pointing out that the bimodality of the log AI distribution may be evidence that the BAL-forming region has clearly delineated physical boundaries.
methods: statistical, catalogues, surveys, quasars: absorption lines
0035-8711
1426-1435
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Scaringi, Simone
88701970-a1b9-41fe-bf55-886716ee3374
Goad, Michael R.
98d06542-81a7-4d7b-a0a5-c79079b9c662
Cottis, Christopher E.
25aa05dc-de5d-4deb-9486-c04d94e871d0
Knigge, Christian
ac320eec-631a-426e-b2db-717c8bf7857e
Scaringi, Simone
88701970-a1b9-41fe-bf55-886716ee3374
Goad, Michael R.
98d06542-81a7-4d7b-a0a5-c79079b9c662
Cottis, Christopher E.
25aa05dc-de5d-4deb-9486-c04d94e871d0

Knigge, Christian, Scaringi, Simone, Goad, Michael R. and Cottis, Christopher E. (2008) The intrinsic fraction of broad-absorption line quasars. Monthly Notices of the Royal Astronomical Society, 386 (3), 1426-1435. (doi:10.1111/j.1365-2966.2008.13081.x).

Record type: Article

Abstract

We carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate of the intrinsic BALQSO fraction from the Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. We first show that the distribution of objects selected by the so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high BALQSO fractions that have recently been inferred from AI-based samples are therefore likely to be overestimated. We then present two new approaches to the classification problem that are designed to be more robust than the AI, but also more complete than the traditional 'balnicity index' (BI). Both approaches yield observed BALQSO fractions around 13.5 per cent, while a conservative third approach suggests an upper limit of 18.3 per cent. Finally, we discuss the selection biases that affect our observed BALQSO fraction. After correcting for these biases, we arrive at our final estimate of the intrinsic BALQSO fraction. This is fBALQSO= 0.17 ± 0.01 (stat) ± 0.03 (sys) with an upper limit of fBALQSO? 0.23 . We conclude by pointing out that the bimodality of the log AI distribution may be evidence that the BAL-forming region has clearly delineated physical boundaries.

Full text not available from this repository.

More information

Published date: 21 May 2008
Keywords: methods: statistical, catalogues, surveys, quasars: absorption lines
Organisations: Astronomy and Space Science

Identifiers

Local EPrints ID: 144205
URI: http://eprints.soton.ac.uk/id/eprint/144205
ISSN: 0035-8711
PURE UUID: a12fe87c-df5e-4034-a153-dea52998fcd4

Catalogue record

Date deposited: 16 Apr 2010 15:21
Last modified: 17 Jul 2019 00:07

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×