The X-ray properties of the most luminous quasars with strong emission-line outflows

Anastasia Shlentsova, Bartolomeo Trefoloni, Matilde Signorini, Guido Risaliti, Elisabeta Lusso, Emanuele Nardini, Franz E. Bauer, Matthew J. Temple, Amy L. Rankine, Gordon T. Richards

First listed 2026-02-06 | Last updated 2026-02-06

Abstract

Strong outflows from active galactic nuclei are frequently observed in objects with lower coronal X-ray luminosity. This intrinsic X-ray weakness is considered a requirement for the formation of radiatively driven winds. To obtain an unbiased view on the connection between X-ray emission and the presence of powerful winds in the most luminous quasar phase, we present an X-ray analysis of a sample of extremely luminous, radio-quiet quasars with signatures of strong outflows in their rest-frame ultraviolet (UV) emission spectra. We study the $Chandra$ X-ray spectral properties of 10 objects, selected from the Sloan Digital Sky Survey Data Release 16 quasar catalogue based on their UV luminosities and ${\rm C}_{\rm IV}$ emission line blueshifts, comparing them to typical optically blue quasars. Our analysis reveals that seven out of 10 quasars in our sample have photon indices $Γ>1.7$. Only two out of 10 objects exhibiting outflows with velocities exceeding 1400 km/s are X-ray 'weak', consistent with the fraction of X-ray 'weak' objects generally observed in quasar populations. Notably, one of the objects identified as X-ray 'weak' is likely an intrinsically X-ray 'normal' quasar that is heavily obscured. We observe a tentative indication at a $\sim$2$σ$ confidence level that the correlation between the excessively low X-ray flux level and the presence of ${\rm C}_{\rm IV}$ emission-line outflows might emerge at wind velocities greater than 3000 km/s. Our study provides additional evidence that the relationship between X-ray emission and the presence of winds is intricate. Our findings emphasise the need for X-ray observations of a larger sample of UV-selected quasars with confirmed strong emission-line outflows to unravel the nuanced interplay between winds and X-ray emission.

Short digest

Chandra spectroscopy of 10 extremely luminous, radio‑quiet SDSS DR16 quasars preselected for strong UV emission‑line outflows (C IV centroid blueshift ≥1400 km/s) finds largely normal coronal emission. Seven of ten show photon indices Γ>1.7, and only two qualify as X‑ray “weak,” with one of those likely an intrinsically normal but heavily obscured quasar. A tentative (~2σ) trend links unusually low X‑ray flux to very fast winds only at v_out ≳3000 km/s. Bottom line: powerful emission‑line winds in the brightest quasars do not generally require suppressed X‑rays, motivating larger unbiased X‑ray samples.

Key figures to inspect

• Figure 1: Use L2500 vs. C IV centroid shift to see how strong blueshifts become ubiquitous at the highest UV luminosities and how the 10‑object main sample was carved out of the 45 preselected targets.
• Figure 2: Inspect the multi‑component fit to the C IV region; verify the outflow component’s blueshift relative to the BLR component (v_out) after masking tellurics/absorbers, confirming the ≥1400 km/s selection and how velocities were measured.
• Figure 3: Locate the sample in the C IV emission‑space map colored by He II EW (MFICA reconstructions for 66,810 DR16 quasars) to gauge whether weak He II—hence softer SEDs—coincide with large C IV blueshifts in this extreme‑luminosity regime.
• Figure 4: Examine the example Chandra fit to read off Γ and any absorption signatures; identify which spectra look flattened/absorbed, consistent with the obscured X‑ray‑‘weak’ outlier versus the Γ>1.7 majority.