Supermassive primordial black holes: a view from clustering of quasars at $z \sim 6$

TL;DR

This study uses quasar clustering data at redshift ~6 to test whether primordial black holes could be the progenitors of supermassive black holes, finding that such a scenario is unlikely based on the observed clustering patterns.

Contribution

The paper provides the first clustering analysis of high-redshift quasars to constrain primordial black hole models for supermassive black hole formation.

Findings

Quasar clustering at z~6 is inconsistent with PBH-based SMBH formation models.

The observed angular correlation function excludes broad PBH parameter space.

Direct collapse of PBH clumps as SMBH progenitors is also disfavored.

Abstract

We investigate a scenario where primordial black holes (PBHs) can be the progenitors of supermassive black holes (SMBHs) observed at $z\sim6$. To this end, we carried out clustering analysis using a sample of 81 quasars at $5.88 <z<6.49$, which is constructed in Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, and 11 quasars in the same redshift range selected from the literature. The resulting angular auto-correlation function (ACF) can be fitted to a power-law form of $\omega_\theta = 0.045^{+0.114}_{-0.106}~\theta^{-0.8}$ over a scale of $0.2\!-\!10$ degrees. We compare the ACF of the quasars to that predicted for the PBH model at $z\sim 6$ and found that such a scenario is excluded for a broad range of parameter space, from which we can conclude that a scenario with PBHs as SMBHs is not viable. We also discuss a model in which SMBHs at $z \sim 6$ originate from the direct collapse of PBH clumps and argue that the observed ACF excludes such a scenario in the context of our PBH model.