Extragalactic X-ray Surveys from Deep to Wide

This is a recording of a talk titled "Extragalactic X-ray Surveys from Deep to Wide" prepared for the "High-Energy Astrophysics and Cosmology in the Era of All-Sky Surveys" conference (2024 October). The speaker is Prof. W.N. Brandt from the Department of Astronomy & Astrophysics at the Pennsylvania State University.

Here is the relevant abstract: I will briefly review what X-ray surveys and their multiwavelength follow-up have revealed about the sources constituting the cosmic X-ray background (CXRB), focusing on extragalactic results from the past 25 years from missions including Chandra, Einstein Probe, INTEGRAL, NuSTAR, SRG, Swift, and XMM-Newton. After demonstrating the general utility of X-ray surveys, I will detail the identification, classification, and basic nature of the detected sources: active galactic nuclei, galaxies, clusters and groups, and transients. Since active galactic nuclei are the dominant contributors to the CXRB, I will present some key insights about their demographics, physics, and ecology revealed by X-ray surveys. I will conclude by describing some unresolved questions and prospects for advancing the field with new observations, future missions, and complementarity with multiwavelength very wide-field surveys.