The XMM deep survey in the CDFS

XI. X-ray spectral properties of 185 bright sources^⋆

¹ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès, 1, 08028 Barcelona, Spain
e-mail: kazushi.iwasawa@icc.ub.edu
² ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
³ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
⁴ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁵ Department of Astonomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802, USA
⁶ Institute of Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
⁷ Department of Physics, 104 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802, USA
⁸ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
⁹ Instituto de Física de Cantabria (CSIC-UC), Avenida de los Castros, 39005 Santander, Spain
¹⁰ Combient MiX AB, PO Box 2150, 40313 Gothenburg, Sweden
¹¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
¹² National Observatory of Athens, V. Paulou & I, Metaxa 15236, Greece
¹³ Agenzia Spaziale Italiana-Unità di Ricerca Scientifica, via del Politecnico, 00133 Roma, Italy
¹⁴ Dipartimento di Fisica, Università degli studi di Napoli Federico II, via Cinthia, 80126 Napoli, Italy
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁶ INFN – Sezione di Napoli, Via Cinthia 9, 80126 Napoli, Italy

Received: 3 December 2019
Accepted: 10 April 2020

Abstract

We present the X-ray spectra of 185 bright sources detected in the XMM-Newton deep survey of the Chandra Deep Field South with the three EPIC cameras combined. The 2–10 keV flux limit of the sample is 2 × 10⁻¹⁵ erg s⁻¹ cm⁻². The sources are distributed over a redshift range of z = 0.1−3.8, with 11 new X-ray redshift measurements 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 were identified, which set the Compton-thick AGN fraction at ≃4%. An exploratory spectral inspection method with two rest-frame X-ray colours and an Fe line strength indicator was 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 with 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, exhibit a puzzlingly low obscuration.