eROSITA's Second Data Release Catalog Delivering the Most Comprehensive High-Energy Census of the Cosmos to Date

The eROSITA (extended ROentgen Survey with an Imaging Telescope Array) telescope, the primary instrument aboard the Russian-German Spektr-RG space observatory, was developed by the Max Planck Institute for Extraterrestrial Physics (MPE) and collaborators to study the soft X-ray night sky. The mission launched in 2019 and has delivered deep, sharp images over very large areas of the sky to map the high-energy Universe. This past summer, the German eROSITA Consortium made its second data release (DR2), the most comprehensive catalog of the X-ray Universe ever released. Combining data from three full-sky scans, the DR2 lists over 1.9 million point-like sources (primarily stars and actively accreting black holes) and about 64,000 extended sources, including galaxy clusters and supernova remnants (neutron stars and active black holes) - almost double the sources in the original release. The catalog includes data from multiple sky passes that were conducted by the observatory every six months to progressively increase depth and sensitivity. As Mara Salvato, the eROSITA spokesperson and chair of the follow-up working group, added: X-ray detection is only the first step. By linking X-ray sources to their counterparts at other wavelengths, we can work out what these objects are, where they sit on the cosmic distance ladder, and build clean, well-defined samples on an unprecedented scale. An illustration of the winds and accretion disk around a supermassive black hole that makes up an AGN. Credit: NASA/M.Weiss (Chandra X-ray Center) DR2 combines data obtained over Spektr-RG's first 556 days of observations, which were stacked to capture more objects with fainter fluxes. The catalog also includes multi-wavelength information that connects detections with their most likely optical and infrared counterparts. From this data, the team concluded that about 88% of the identified sources are extragalactic, predominantly from the actively accreting supermassive black holes (SMBHs) at the center of galaxies beyond our own. This release also coincides with the Sloan Digital Sky Survey's twentieth release (SDSS DR20), which includes considerable optical spectroscopy provided by eROSITA-DE's surveys. These two datasets represent the culmination of almost a decade of scientific collaboration between the two survey efforts. Combining the data has enabled one of the largest and most detailed studies of SMBHs to date. From this, researchers will be able to construct 3D maps of active black holes and track their evolution over cosmic time. Said William Roster, the lead author of the corresponding study: The most luminous black holes at high redshift are like needles in a haystack. Thanks to DR2, we found more needles than expected, suggesting that rapidly growing black holes were more abundant in the early Universe than previously thought. “This is a dataset of unprecedented scale and completeness, now in the hands of the global astronomical community," added eROSITA Principal Investigator Andrea Merloni. "With nearly 2 million sources, DR2 provides a unique foundation for discoveries ranging from rare objects to large-scale population studies.” Further Reading: MPE