New Constraints on Quasar Evolution: Broad Line Velocity Shifts over $1.5\lesssim z\lesssim 7.5$

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 $1.5\le z\le 7.5$. We fit the main Broad Emission Lines (BELs) in the rest-frame range $1280\text{A˚}\le \lambda \le 3000\text{A˚}$ (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 $1.5\gtrsim z\gtrsim 6$. 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.

Accepted for publication in MNRAS. 14 pages, 14 Figures, 2 Tables. Revised version to match the accepted one - results unchanged. Supplementary material for appendix A available at : www.homepages.ucl.ac.uk/~ucapram/QSOBEL_shifts_supp_material.tar.gz

References in corpus (20)

• A Catalog of Quasar Properties from SDSS DR7
• A luminous quasar at a redshift of z = 7.085
• Biases in Virial Black Hole Masses: An SDSS Perspective
• The Sloan Digital Sky Survey Quasar Catalog: twelfth data release
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• Faint AGNs at z>4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe
• Physical properties of 15 quasars at $z\gtrsim 6.5$
• Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
• The WISSH Quasars Project I. Powerful ionised outflows in hyper-luminous quasars
• A downturn in intergalactic CIV as redshift 6 is approached
• XQ-100: A legacy survey of one hundred 3.5 < z < 4.5 quasars observed with VLT/XSHOOTER
• Two bright z > 6 quasars from VST ATLAS and a new method of optical plus mid-infra-red colour selection
• The discovery of the first luminous z~6 quasar in the UKIDSS Large Area Survey
• Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
• A deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641
• Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641
• Black hole obscuration and duty cycles mediated by AGN feedback in high redshift galaxies
• Kinematics of CIV and [OIII] emission in luminous high-redshift quasars
• A new bright z=6.82 quasar discovered with VISTA: VHS J0411-0907

Cited by in corpus (3)

• A Luminous Quasar at Redshift 7.642
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928