XMM-Newton observations of the Lockman Hole: X-ray source catalogue and number counts

TL;DR

This paper presents a deep X-ray source catalogue from XMM-Newton observations of the Lockman Hole, providing detailed source counts, spectral analysis, and insights into Compton-thick AGN populations at unprecedented sensitivity levels.

Contribution

It offers the deepest XMM-Newton X-ray survey of the Lockman Hole, including a new logN-logS relation for Compton-thick AGN and analysis of X-ray colours for source classification.

Findings

Detected 409 X-ray sources within the surveyed area.

Measured sensitivity limits down to 1.9×10^-16 erg cm^-2 s^-1 in the 0.5-2.0 keV band.

Estimated a 6% fraction of Compton-thick AGN candidates, consistent with models.

Abstract

The Lockman Hole field represents the sky area of lowest Galactic line-of-sight column density N_H=5.7X10^19 cm^-2. It was observed by the XMM-Newton X-ray observatory in 18 pointings for a total of 1.16 Msec (raw EPIC pn observing time) constituting the deepest XMM-Newton exposure so far. We present a catalogue of the X-ray sources detected in the central 0.196 deg^2 of the field and discuss the derived number counts and X-ray colours. In the 0.5--2.0 keV band, a sensitivity limit (defined as the faintest detectable source)of 1.9X10^-16 erg cm^-2 s^-1 was reached. The 2.0--10.0 keV band and 5.0--10.0 keV band sensitivity limits were 9X10^-16 erg cm^-2 s^-1 and 1.8X10^-15 erg cm^-2 s^-1, respectively.A total of 409 sources above a detection likelihood of 10 (3.9 sigma) were found within a radius of 15' off the field centre, of which 340, 266, and 98 sources were detected in the soft, hard, and very hard bands, respectively. The number counts in each energy band are in close agreement with results from previous surveys and with the synthesis models of the X-ray background. A 6% of Compton-thick source candidates have been selected from the X-ray colour-colour diagram. This fraction is consistent with the most recent predictions of X-ray background population synthesis models at our flux limits. We also estimated, for the first time, the logN-logS relation for Compton-thick AGN.