Reconstructing PTA measurements via early seeding of supermassive black holes

Abstract

Motivated by recent findings that PTA's nHz signal may be dominated by supermassive black hole (SMBH) binaries ($M\gtrsim 10^9{M}_{\odot }$), and high redshift quasar observations revealing unexpectedly massive SMBHs, we calculate the implications of early seeded SMBHs for the PTA signal. As an application, we explore two prominent scenarios of high-$z$ SMBHs seeding mechanisms: direct collapse black holes (DCBHs) and collapse of Dark Stars. We show that Dark Star seeded SMBHs, with comoving seed number density of $\mathcal{O}(10^{-3}){\mathrm{Mpc}}^{-3}$ can be the dominant contributor to the PTA signal while the DCBH channel may contribute sub-dominantly. We also suggest ways to place an upper bound on the seed number density.

Accepted as PRD Letter