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New constraints on quasar evolution: broad-line velocity shifts over 1.5 ≲ z ≲ 7.5

Meyer, RA; Bosman, SEI; Ellis, RS; (2019) New constraints on quasar evolution: broad-line velocity shifts over 1.5 ≲ z ≲ 7.5. Monthly Notices of the Royal Astronomical Society , 487 (3) pp. 3305-3323. 10.1093/mnras/stz1504. Green open access

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Abstract

We present the results of a model-independent investigation of the rest-frame UV spectra from a comprehensive sample of $394$ quasars in the redshift range $1.5\leq z \leq 7.5$. We fit the main Broad Emission Lines (BELs) in the rest-frame range $1280 \text{\AA} \leq \lambda \leq 3000 \text{\AA}$ (O I, C II, Si IV, C III, C IV and Mg II) with a lightly-supervised spline fitting technique. Redshifts are derived from the peaks of each fitted BEL and used to compute relative velocity shifts. We show that our method gives unbiased velocity shifts and is insensitive to spectral resolution and instrumental parameters. It is found that the average blueshift of the \cfour\, line with respect to several low-ionisation lines in luminosity-matched samples does not significantly evolve over $1.5\gtrsim z\gtrsim6$. However, the average blueshift increases significantly by a factor $\sim 2.5$ at $z\gtrsim 6$. We propose that this redshift evolution can be explained by \cfour\, winds launched perpendicularly to an accretion disk with increased torus opacity at high-redshift, coupled with a potential orientation-driven selection bias. Our results open new exciting avenues of investigation into young quasars in the reionisation epoch.

Type: Article
Title: New constraints on quasar evolution: broad-line velocity shifts over 1.5 ≲ z ≲ 7.5
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stz1504
Publisher version: http://dx.doi.org/10.1093/mnras/stz1504
Language: English
Additional information: This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: galaxies: evolution, quasars: emission lines
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10075330
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