Can X-Ray Observations Improve Optical-UV-based Accretion-rate Estimates for Quasars?

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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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Marlar, Andrea May 23, 2022.

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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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10 p.

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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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  • The Astrophysical Journal, 931(1), IOP Science, May 2022

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  • Publication Title: The Astrophysical Journal
  • Volume: 931
  • Issue: 1
  • Article Identifier: 41
  • Pages: 10
  • Peer Reviewed: Yes

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  • May 23, 2022

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  • Sept. 30, 2022, 11:33 a.m.

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  • Nov. 1, 2022, 8:39 a.m.

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Marlar, Andrea. 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 April 14, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Science.

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