eRASS Hard X-ray selected AGNs

The Bayesian statistics-based code NWAY was used to identify the counterparts for the X-ray sources. These sources were classified based on their multi-wavelength properties, and the literature was searched to identify spectroscopic redshifts, which further inform the source classification. A total of 2547 sources were found to have good-quality counterparts, and 111 of these have been detected only in the hard band.

The median redshift of the extragalactic sources is ~0.19. Compared with other hard X-ray selected surveys, the eROSITA hard sample covers a larger redshift range and probes dimmer sources, providing a complementary and expanded sample as compared to Swift BAT. Examining the column density distribution of missed and detected eROSITA sources present in the follow-up catalogue of Swift BAT 70 month sources, it is demonstrated that eROSITA can detect obscured sources with column densities >10^23cm^-2^ corresponding to ~14% of the full sample, but that the completeness drops rapidly thereafter.

A sample of hard-only sources, many of which are likely to be obscured AGN with column densities ~10^23cm^-2^, is also presented and discussed. We caution that a large number of hard-only sources are believed to be spurious, based on simulations, and that additional cuts on counterpart quality or requiring spectroscopic redshifts should be applied to use this sample. X-ray spectral fitting reveals that these sources have extremely faint soft X-ray emission and their optical images suggest that they are found in more edge-on galaxies with lower b/a.

The first eROSITA all-sky survey provided the first imaging survey above 2keV, and the resulting X-ray catalogue has been demonstrated to be a powerful tool for understanding AGN, in particular the heavily obscured AGN found in the hard-only sample.