A systematic cross-search for radio/infrared counterparts of XMM-Newton sources

TL;DR

This study created a catalog of radio, infrared, and X-ray source counterparts, revealing that most high-latitude X-ray sources are active galactic nuclei, while low-latitude sources are likely galactic objects, using a rigorous cross-matching method.

Contribution

The paper introduces a new, highly restrictive cross-correlation catalog of multi-wavelength sources with statistical significance, aiding in the identification of X-ray sources.

Findings

3320 high-confidence radio/X-ray coincidences identified

Less than 1% chance coincidence rate

Most high-latitude X-ray sources are AGN, while low-latitude sources are galactic objects

Abstract

We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b| >= 10^\circ). At low galactic latitudes (|b| <= 10^\circ) most of unidentified X-ray sources (~94%) lie at |b| <= 2^\circ. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.