Characterising SMSS J2157--3602, the most luminous known quasar, with accretion disc models

TL;DR

This paper introduces a Bayesian accretion disc fitting method applied to the most luminous known quasar, providing detailed estimates of black hole mass, luminosity, and efficiency, and demonstrating its potential to complement existing mass estimation techniques.

Contribution

The paper develops and tests a new Bayesian accretion disc fitting approach using thin and slim disc models on a high-redshift quasar, offering improved black hole property constraints.

Findings

Black hole mass estimated at log(M_AD/M_sun)=10.31 with uncertainties.

Bolometric luminosity determined as log(L_bol/erg s^{-1})=47.87.

Eddington ratio of approximately 0.29 was derived.

Abstract

We develop an accretion disc (AD) fitting method, utilising thin and slim disc models and Bayesian inference with the Markov-Chain Monte-Carlo approach, testing it on the most luminous known quasar, SMSS J215728.21-360215.1, at redshift $z=4.692$. With a spectral energy distribution constructed from near-infrared spectra and broadband photometry, the AD models find a black hole mass of $\log(M_{\rm{AD}}/M_{\odot}) = 10.31^{+0.17}_{-0.14}$ with an anisotropy-corrected bolometric luminosity of $\log{(L_{\rm{bol}}/\rm{erg\,s^{-1}})} = 47.87 \pm 0.10$, and derive an Eddington ratio of $0.29^{+0.11}_{-0.10}$ as well as a radiative efficiency of $0.09^{+0.05}_{-0.03}$. Using the near-infrared spectra, we estimate the single-epoch virial black hole mass estimate to be $\log(M_{\rm{SE}}/M_{\odot}) = 10.33 \pm 0.08$, with a monochromatic luminosity at 3000\AA\ of $\log{(L(\rm{3000\text{\AA}})/\rm{erg\,s^{-1}})} = 47.66 \pm 0.01$. As an independent approach, AD fitting has the potential to complement the single-epoch virial mass method in obtaining stronger constraints on properties of massive quasar black holes across a wide range of redshifts.