The XMM deep survey in the CDFS XI. X-ray properties of 185 bright sources

TL;DR

This study analyzes X-ray spectra of 185 bright sources from the XMM-Newton deep survey of the Chandra Deep Field South, revealing properties of AGN, obscuration trends, and identifying potential Compton-thick AGN candidates.

Contribution

Introduces an exploratory spectral inspection method using X-ray colours and Fe line indicators for pre-selecting Compton-thick AGN candidates.

Findings

Obscured AGN are more common at higher redshifts.

Approximately 4% of sources are Compton-thick AGN candidates.

Detected broad Fe K lines in about 30% of unobscured AGN.

Abstract

We present X-ray spectra of 185 bright sources detected in the XMM-Newton deep survey of the Chandra Deep Field South, combining the three EPIC cameras. The 2-10 keV flux limit of the sample is 2e-15 erg/s/cm2. The sources are distributed over a redshift range of z=0.1-3.8. Eleven new X-ray redshift measurements are included. A spectral analysis was performed using a simple model to obtain absorbing column densities, rest-frame 2-10 keV luminosities and Fe K line properties of 180 sources at z>0.4. Obscured AGN are found to be more abundant toward higher redshifts. Using the XMM-Newton data alone, seven Compton-thick AGN candidates are identified, which makes the Compton-thick AGN fraction to be ~4%. An exploratory spectral inspection method with two rest-frame X-ray colours and an Fe line strength indicator is introduced and tested against the results from spectral fitting. This method works reasonably well to characterise a spectral shape and can be useful for a pre-selection of Compton-thick AGN candidates. We found six objects exhibiting broad Fe K lines out of 21 unobscured AGN of best data quality, implying a detection rate of ~30%. Five redshift spikes, each of which has more than six sources, are identified in the redshift distribution of the X-ray sources. Contrary to the overall trend, the sources at the two higher-redshift spikes at z=1.61 and z=2.57 have puzzlingly low obscuration.