Journal Article

Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy Survey

S. Perrotta, V. D'Odorico, J. X. Prochaska, S. Cristiani, G. Cupani, S. Ellison, S. López, G. D. Becker, T. A. M. Berg, L. Christensen, K. D. Denney, F. Hamann, I. Pâris, M. Vestergaard and G. Worseck

in Monthly Notices of the Royal Astronomical Society

Volume 462, issue 3, pages 3285-3301
ISSN: 0035-8711
Published online July 2016 | e-ISSN: 1365-2966 | DOI:
Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy Survey

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We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5 < zem < 4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an ∼8σ excess in the C iv number density within 10 000 km s− 1 of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km s− 1 cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10 000 km s− 1 when weak absorbers (equivalent width < 0.2 Å) are also considered. We infer N v is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C ii) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.

Keywords: galaxies: high-redshift; intergalactic medium; quasars: absorption lines

Journal Article.  14114 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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