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CIV Emission as a Vector for Improving Quasars as Standard Candles

Presentation #101.15 in the session AGN & Quasars — iPoster Session.

Published onJun 29, 2022
CIV Emission as a Vector for Improving Quasars as Standard Candles

Risaliti & Lusso (2015) have developed a method for using quasars to constrain cosmological parameters. Their method depends on the non-linear relationship between X-ray and optical/UV flux (αox) and reducing possible sources of scatter in that relationship. Scatter could come in the form of dust reddening or gas absorption and/or variability between the optical and X-ray epochs. We find that there is potential for applying a CIV emission-line-based correction in addition to (or instead of) cutting absorbed objects — even after accounting for the trend in X-ray and optical/UV flux with luminosity (Δαox). It would appear that a simple multi-dimensional linear fit to Δαox as a function of both X-ray photon index (Gamma) and CIV emission-line properties could be used to make corrections to αox for individual objects in a way that would further reduce the scatter in the (corrected) αox distribution. Doing so could enable the development of a relationship similar to that which allows for Type Ia supernovae to have a “standardizable” luminosity. Moreover, we note that, the CIV emission-line properties are less susceptible to variability than αox and could be used to further reduce the scatter in αox by identifying individual objects with “wrong” values of αox caused by variability between the optical and X-ray epochs, enabling further improvement of cosmological analyses with quasars. This work is based in part upon support from the National Science Foundation under Grant No. 1908716.

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