X-ray Coverage of the LSST Deep-Drilling Fields: Current XMM-SERVS Results and Future Prospects

Cosmic X-ray surveys over the past two decades have played a critical role in transforming our understanding of growing supermassive black holes (SMBHs) in the distant universe. I will describe one key XMM-Newton survey, recently completed, advancing this effort: the 13.1 deg² XMM-SERVS survey. XMM-SERVS has successfully mapped three Rubin LSST Deep-Drilling Fields (DDFs) at 50 ks XMM-Newton depth, focusing on the SERVS areas of CDF-S, XMM-LSS, and ELAIS-S1. These fields have first-rate multiwavelength coverage already and are LSST/DES DDFs, MOONS/PFS massive spectroscopy fields, prime TolTEC/ALMA fields, and SDSS-V/4MOST multi-object reverberation-mapping fields. About 12,000 X-ray sources have been detected and characterized, the majority of which (86%) are active galactic nuclei (AGNs), and these are presently being studied. I will briefly summarize ongoing science investigations in these fields, including multiwavelength fitting of infrared-to-X-ray spectral energy distributions, identification of the most highly X-ray obscured AGNs, combined radio/X-ray AGN selection, and X-ray studies of distant active dwarf galaxies. I will discuss future prospects for improving coverage of the LSST DDFs with XMM-Newton and Chandra, hopefully contemporaneously with ongoing Rubin LSST observations. I will also briefly highlight how the proposed STAR-X MIDEX mission could obtain much more sensitive X-ray coverage of the LSST DDFs, thereby illuminating the growth modes of the first SMBHs, obscured SMBH growth/feedback through the era of galaxy assembly, extreme SMBH accretion physics, novel X-ray transients, high-redshift clusters, and protoclusters.