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

Abstract

We investigate a scenario where primordial black holes (PBHs) can be the progenitors of supermassive black holes (SMBHs) observed at $z\sim 6$. 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 ${\omega }_{\theta }=0.045_{-0.106}^{+0.114}{\theta }^{-0.8}$ 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.

23 pages, 7 figures