Speaker
Description
Extragalactic X-ray surveys have transformed our view of the high-energy universe, revealing the populations that produce the cosmic X-ray background (CXRB) and reshaping our understanding of black-hole growth and cosmic structure. I will review what X-ray surveys and their multiwavelength follow-up have uncovered about these populations over the past 27 years, drawing on results from missions including Chandra, Einstein Probe, INTEGRAL, MAXI, NuSTAR, Spektr-RG, Swift, and XMM-Newton. I will first discuss the identification, classification, and basic nature of the extragalactic sources detected in X-ray surveys, including active galactic nuclei (AGNs), galaxies, clusters and groups, and transients. Since AGNs dominate the CXRB, I will then highlight key insights into their demographics, physics, and ecology revealed by X-ray surveys. These include recent results on the drivers of AGN evolution, AGN-galaxy connections, highly obscured AGNs, high-redshift AGNs, dwarf-galaxy AGNs, as well as hypervariable AGNs and nuclear X-ray transients. I will conclude by outlining major unresolved questions and prospects for advancing the field through new observations, future missions, and complementarity with multiwavelength wide-field surveys.