Exploring the properties of the obscured hyperluminous quasar COS-87259 at z=6.853

TL;DR

This study characterizes the properties of a highly obscured, hyperluminous quasar at redshift 6.853 using advanced Bayesian SED fitting, revealing its dominant AGN contribution, black hole mass, and star formation rate, with implications for early universe quasar populations.

Contribution

Introduces a Bayesian SED fitting approach with radiative transfer models to analyze obscured quasars at high redshift, providing detailed physical parameters.

Findings

AGN fraction 86-92%

Black hole mass 1.8-3.2 billion solar masses

Star formation rate ~2000 solar masses per year

Abstract

In this paper we explore the properties of the z=6.853 obscured hyperluminous quasar COS-87259, discovered in the Cosmological Evolution Survey (COSMOS) field, with our recently developed Bayesian spectral energy distribution (SED) fitting code SMART (Spectral energy distributions Markov chain Analysis with Radiative Transfer models). SMART fits SEDs exclusively with multicomponent radiative transfer models that constitute four different types of pre-computed libraries for the active galactic nucleus (AGN) torus, the starburst and the spheroidal or disc host. We explore two smooth radiative transfer models for the AGN torus and two two-phase models, in order to put constraints on the AGN fraction of the galaxy, the black hole mass and its star formation rate (SFR). We find that either of the smooth tapered disc or the two-phase flared disc models provide a good fit to the SED of COS-87259. The best-fitting models predict an AGN fraction in the range 86-92 per cent, a bolometric AGN luminosity of 5.8-10.3 x 10^13 Lo, a black hole mass of 1.8-3.2 x 10^9 Mo (assuming the quasar is accreting at the Eddington limit) and an SFR in the range 1985-2001 Mo/yr. The predicted space density of such objects in the redshift range 4-7 is about 20 times more than that of co-eval unobscured quasars.