Abundance of LIGO/Virgo Black Holes from Microlensing Observations of Quasars with Reverberation Mapping Size Estimates

TL;DR

This study uses quasar microlensing observations combined with reverberation mapping to constrain the abundance of stellar-mass black holes, finding they constitute less than 0.4% of dark matter, aligning with LIGO/Virgo merger data.

Contribution

It provides new upper limits on the abundance of LIGO/Virgo-mass black holes using quasar microlensing, considering a mixed population and dark matter components.

Findings

Black holes of ~30 M_sun make up less than 0.4% of total matter.

Stellar contribution estimated at 16%, consistent with previous studies.

Results exclude primordial black holes as significant dark matter components.

Abstract

Assuming a population of Black Holes (BHs) with masses in the range inferred by LIGO/Virgo from BH mergers, we use quasar microlensing observations to estimate their abundances. We consider a mixed population of stars and BHs and the presence of a smooth dark matter component. We adopt reverberation mapping estimates of the quasar size. According to a Bayesian analysis of the measured microlensing magnifications, a population of BHs with masses $\sim$ 30$M_{\odot}$ constitutes less than 0.4 % of the total matter at 68 % confidence level (less than 0.9 % at 90 % confidence). We have explored the whole mass range of LIGO/Virgo BHs finding that this upper limit ranges from 0.5 % to 0.4 % at 68 % C.L. (from 1.1 % to 0.9 % at 90 % C.L.) when the BHs mass change from 10 to 60$M_{\odot}$. We estimate a 16 % contribution from the stars, in agreement with previous studies based on a single mass population that do not consider explicitly the presence of BHs. These results are consistent with the estimates of BH abundances from the statistics of LIGO/Virgo mergers and rule out that PBHs (or any type of compact objects), in this mass range constitute a significant fraction of the dark matter.