The ROSAT Deep Survey II. Optical identification, photomettry and spectra of sources in the Lockman field

TL;DR

This paper presents optical identification, photometry, and spectra for 50 X-ray sources in the Lockman field from the ROSAT Deep Survey, classifying most sources as AGNs and other objects, and discusses the identification process.

Contribution

It introduces a systematic process with five ID classes for optical identification of X-ray sources in deep surveys, enhancing source classification accuracy.

Findings

39 AGNs identified among 50 X-ray sources

3 galaxy groups and 1 galaxy identified

4 sources remain unidentified, with some having high X-ray to optical flux ratios

Abstract

The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the $0.5 - 2$ keV band larger than 5.5 $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ in the Lockman field (Hasinger et al., Paper I). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux. Keywords: surveys -- galaxies: active -- quasars: emission lines -- galaxies: Seyfert -- X-rays: galaxies