Article presents a study utilizing a carefully selected sample of 53 radio-quiet quasars that have Hβ and C iv λ1549 spectroscopy as well as Chandra coverage, to search for a robust accretion-rate indicator for quasars, particularly at the highest-accessible redshifts (z ∼ 6–7).
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Article presents a study utilizing a carefully selected sample of 53 radio-quiet quasars that have Hβ and C iv λ1549 spectroscopy as well as Chandra coverage, to search for a robust accretion-rate indicator for quasars, particularly at the highest-accessible redshifts (z ∼ 6–7).
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Abstract: Current estimates of the normalized accretion rates of quasars (L/LEdd) rely on measuring the velocity widths of broad optical-UV emission lines (e.g., Hβ and Mg ii λ2800). However, such lines tend to be weak or inaccessible in the most distant quasars, leading to increasing uncertainty in L/LEdd estimates at z > 6. Utilizing a carefully selected sample of 53 radio-quiet quasars that have Hβ and C iv λ1549 spectroscopy as well as Chandra coverage, we searched for a robust accretion-rate indicator for quasars, particularly at the highest-accessible redshifts (z ∼ 6–7). Our analysis explored relationships between the Hβ-based L/LEdd, the equivalent width (EW) of C iv, and the optical-to-X-ray spectral slope (αox). Our results show that EW(C iv) is the strongest indicator of the Hβ-based L/LEdd parameter, consistent with previous studies, although significant scatter persists particularly for sources with weak C iv lines. We do not find evidence for the αox parameter improving this relation, and we do not find a significant correlation between αox and Hβ-based L/LEdd. This absence of an improved relationship may reveal a limitation of our sample. X-ray observations of additional luminous sources, found at z ≳ 1, may allow us to mitigate the biases inherent in our archival sample and test whether X-ray data could improve L/LEdd estimates. Furthermore, deeper X-ray observations of our sources may provide accurate measurements of the hard-X-ray power-law photon index (Γ), which is considered an unbiased L/LEdd indicator. Correlations between EW(C iv) and αox with a Γ-based L/LEdd may yield a more robust prediction of a quasar normalized accretion rate.
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Marlar, Andrea; Shemmer, Ohad; Brotherton, Michael S.; Richards, Gordon T. & Dix, Cooper.Can X-Ray Observations Improve Optical-UV-based Accretion-rate Estimates for Quasars?,
article,
May 23, 2022;
(https://digital.library.unt.edu/ark:/67531/metadc1998730/:
accessed July 15, 2025),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT College of Science.
