English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

In this work we use a sample of 318 radio-quiet quasars (RQQ) to investigatethe dependence of the ratio of optical/UV flux to X-ray flux, alpha_ox, and theX-ray photon index, Gamma_X, on black hole mass, UV luminosity relative toEddington, and X-ray luminosity relative to Eddington. Our sample is drawn fromthe SDSS, with X-ray data from ROSAT and Chandra, and optical data mostly fromthe SDSS; 153 of these sources have estimates of Gamma_X from Chandra. Weestimate M_BH using standard estimates derived from the Hbeta, Mg II, and C IVbroad emission lines. Our sample spans a broad range in black hole mass (10^6 <M_BH / M_Sun < 10^10) and redshift (z < 4.8). We find that alpha_ox increaseswith increasing M_BH and L_UV / L_Edd, and decreases with increasing L_X /L_Edd. In addition, we confirm the correlation seen in previous studies betweenGamma_X and M_BH and both L_UV / L_Edd and L_X / L_Edd; however, we also findevidence that the dependence of Gamma_X of these quantities is not monotonic,changing sign at M_BH ~ 3 x 10^8 M_Sun. We argue that the alpha_ox correlationsimply that the fraction of bolometric luminosity emitted by the accretion disk,as compared to the corona, increases with increasing accretion rate relative toEddington. In addition, we argue that the Gamma_X trends are caused by adependence of X-ray spectral index on accretion rate. We discuss our resultswithin the context of accretion models with comptonizing corona, and discussthe implications of the alpha_ox correlations for quasar feedback. To date,this is the largest study of the dependence of RQQ X-ray parameters on blackhole mass and related quantities, and the first to attempt to correct for thelarge statistical uncertainty in the broad line mass estimates.

Observational Constraints on the Dependence of Radio-Quiet Quasar X-ray Emission on Black Hole Mass and Accretion Rate