Expectations for Horizon-Scale Supermassive Black Hole Population Studies with the ngEHT

TL;DR

This paper estimates the capabilities of the next-generation Event Horizon Telescope (ngEHT) to identify supermassive black hole shadows and measure their masses and spins, using synthetic data and a geometric emission model.

Contribution

It introduces a simple geometric model for polarized emission around black holes and assesses ngEHT's potential to constrain black hole parameters with simulated datasets.

Findings

ngEHT can potentially measure ~50 black hole masses

ngEHT can potentially measure ~30 black hole spins

ngEHT can potentially identify ~7 black hole shadows

Abstract

We present estimates for the number of supermassive black holes (SMBHs) for which the next-generation Event Horizon Telescope (ngEHT) can identify the black hole ``shadow,'' along with estimates for how many black hole masses and spins the ngEHT can expect to constrain using measurements of horizon-resolved emission structure. Building on prior theoretical studies of SMBH accretion flows and analyses carried out by the Event Horizon Telescope (EHT) collaboration, we construct a simple geometric model for the polarized emission structure around a black hole, and we associate parameters of this model with the three physical quantities of interest. We generate a large number of realistic synthetic ngEHT datasets across different assumed source sizes and flux densities, and we estimate the precision with which our defined proxies for physical parameters could be measured from these datasets. Under April weather conditions and using an observing frequency of 230~GHz, we predict that a ``Phase 1'' ngEHT can potentially measure $\sim$50 black hole masses, $\sim$30 black hole spins, and $\sim$7 black hole shadows across the entire sky.