2021/08/31 by Dominic W. Pesce, Daniel C. M. Palumbo, Ramesh Narayan +7 · 1 citation
Physics and Astronomy · #astro-ph.HE #astro-ph.CO
paper · pdf · doi:10.3847/1538-4357/ac2eb5
37 pages, 18 figures, published in ApJ
arxiv created 2022/01/10 · arxiv updated 2022/01/11
We present estimates for the number of shadow-resolved supermassive black hole (SMBH) systems that can be detected using radio interferometers, as a function of angular resolution, flux density sensitivity, and observing frequency. Accounting for the distribution of SMBHs across mass, redshift, and accretion rate, we use a new semi-analytic spectral energy distribution model to derive the number of SMBHs with detectable and optically thin horizon-scale emission. We demonstrate that (sub)millimeter interferometric observations with ∼0.1 μas resolution and ∼1 μJy sensitivity could access >106 SMBH shadows. We then further decompose the shadow source counts into the number of black holes for which we could expect to observe the first- and second-order lensed photon rings. Accessing the bulk population of first-order photon rings requires \lesssim2 μas resolution and \lesssim0.5 mJy sensitivity, while doing the same for second-order photon rings requires \lesssim0.1 μas resolution and \lesssim5 μJy sensitivity. Our model predicts that with modest improvements to sensitivity, as many as ∼5 additional horizon-resolved sources should become accessible to the current Event Horizon Telescope (EHT), while a next-generation EHT observing at 345 GHz should have access to ∼3 times as many sources. More generally, our results can help guide enhancements of current arrays and specifications for future interferometric experiments that aim to spatially resolve a large population of SMBH shadows or higher-order photon rings.