The correlations between optical/UV broad lines and X-ray emission for a large sample of quasars. Issue 1 (6th December 2019)

• Record Type: Journal Article
• Authors: Timlin, John D; Brandt, W N; Ni, Q; Luo, B; Pu, Xingting; Schneider, D P; Vivek, M; Yi, W
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 492:Issue 1(2020)
• Page Start: 719
• Page End: 741
• Publication Date: 2019-12-06
• Subjects: galaxies: active -- quasars: emission lines -- quasars: general -- X-rays: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz3433
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present Chandra observations of 2106 radio-quiet quasars in the redshift range 1.7 ≤ z ≤ 2.7 from the Sloan Digital Sky Survey (SDSS), through data release 14 (DR14), that do not contain broad absorption lines in their rest-frame ultraviolet (UV) spectra. This sample adds over a decade worth of SDSS and Chandra observations to our previously published sample of 139 quasars from SDSS DR5 that is still used to correlate X-ray and optical/UV emission in typical quasars. We fit the SDSS spectra for 753 of the quasars in our sample that have high-quality (exposure time ≥ 10 ks and off-axis observation angle ≤ 10 arcmin) X-ray observations, and analyse their X-ray-to-optical spectral energy distribution properties (αox and Δαox ) with respect to the measured C iv and Mg ii emission-line rest-frame equivalent width (EW) and the C iv emission-line blueshift. We find significant correlations (at the ≥99.99 per cent level) between αox and these emission-line parameters, as well as between Δαox and $\rm{C \, \small{IV}}$ EW. Slight correlations are found between Δαox and $\rm{C \, \small{IV}}$ blueshift, $\rm{Mg \, \small{II}}$ EW, and the $\rm{C \, \small{IV}}$ EW to $\rm{Mg \, \small{II}}$ EW ratio. The best-fitting trend in each parameter space is used to compare the X-ray weakness (Δαox ) and optical/UV emission properties of typical quasars and weak-line quasars (WLQs). The WLQs typically exhibit weaker X-ray emission than predicted by the typical quasar relationships. The best-fitting relationships for our typical quasars are consistent with predictions from the disc–wind quasar model. The behaviour of the WLQs compared to our typical quasars can be explained by an X-ray 'shielding' model.