X-ray Coverage of the LSST Deep-Drilling Fields: Latest XMM-Newton Results and STAR-X 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 survey, recently completed, advancing this effort: the 13.1 deg² XMM-SERVS survey. XMM-SERVS has successfully mapped three 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, dwarf AGN studies, and combined radio/X-ray AGN investigations. I will also highlight how the proposed STAR-X MIDEX mission will obtain much more sensitive X-ray coverage of the LSST DDFs as it conducts its 12 deg² Deep and 300 deg² Medium-Deep time-domain surveys. STAR-X will detect about 74,000 X-ray sources in its planned Deep surveying of the DDFs and thereby illuminate the growth modes of the first SMBHs, obscured SMBH growth through the era of galaxy assembly, novel X-ray transients, high-redshift clusters, and protoclusters.