# Rapid Black Hole Growth at the Dawn of the Universe: A Super-Eddington Quasar at z=6.6

## TL;DR

This study analyzes a high-redshift quasar at z=6.6, revealing rapid super-Eddington black hole growth with a small, hot accretion disc and super-solar metallicity, challenging standard thin disc models and indicating early SMBH evolution.

## Contribution

It provides the first detailed spectral energy distribution modeling of a z=6.6 quasar, demonstrating super-Eddington accretion and a very blue continuum slope, suggesting rapid black hole growth in the early universe.

## Key findings

- Black hole mass estimated at ~10^8 solar masses.
- The continuum slope is significantly bluer than standard models predict.
- The quasar is accreting at super-Eddington rates, with L_bol/L_Edd ≥ 9.

## Abstract

We present the analysis of a new near-infrared (NIR) spectrum of a recently discovered $z=6.621$ quasar PSO J006+39 in an attempt to explore the early growth of supermassive black holes (SMBHs). This NIR (rest-frame ultraviolet, UV) spectrum shows blue continuum slope and rich metal emission lines in addition to Ly$\alpha$ line. We utilize the MgII line width and the rest frame luminosity $L_\text{3000\AA}$ to find the mass of SMBH ($M_\text{BH}$) to be $\sim 10^8 M_\odot$, making this one of the lowest mass quasars at high redshift. The power-law slope index ($\alpha_\lambda$) of the continuum emission is $-2.94\pm0.03$, significantly bluer than the slope of $\alpha_\lambda=-7/3$ predicted from standard thin disc models. We fit the spectral energy distribution (SED) using a model which can fit local SMBHs, which includes warm and hot Comptonisation powered by the accretion flow as well as an outer standard disc. The result shows that the very blue slope is probably produced by a small radial ($\sim230$ gravitational radius, $R_\text{g}$) extent of the standard accretion disc. All plausible SED models require that the source is super-Eddington ($L_\text{bol}/L_\text{Edd} \gtrsim 9$), so the apparently small disc may simply be the inner funnel of a puffed up flow, and clearly the SMBH in this quasar is in a rapid growth phase. We also utilize the rest-frame UV emission lines to probe the chemical abundance in the broad line region (BLR) of this quasar. We find that this quasar has super solar metallicity through photoionization model calculations.