Ultra-deep catalog of X-ray groups in the Extended Chandra Deep Field South^⋆

¹ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, 00014 Helsinki, Finland
e-mail: alexis.finoguenov@helsinki.fi
² University of Maryland Baltimore County, 1000 Hilltop circle, Baltimore, MD 21250, USA
³ National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
⁴ Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall Irvine, CA 92697, USA
⁵ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22, Chile
⁸ Millennium Institute of Astrophysics  
⁹ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301, USA
¹⁰ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹¹ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
¹² Institute for the Physics and Mathematics of the Universe, University of Tokyo, 2778582 Kashiwa, Japan
¹³ Department of Astronomy & Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802, USA
¹⁴ Key Laboratory for Research in Galaxies and Cosmology, Center for Astrophysics, Department of Astronomy, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, 230026 Anhui, PR China
¹⁵ Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, CA 91101, USA
¹⁶ Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
¹⁷ Dr. Karl Remeis-Observatory & ECAP, University Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany
¹⁸ Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA
¹⁹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
²⁰ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
²¹ INAF–Osservatorio Astrofisico di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
²² Dipartimento di Fisica e Scienze della Terra, Universita degli Studi di Ferrara, via Saragat 1, 44122 Ferrara, Italy
²³ California Institute of Technology, MS 249-17 Pasadena, CA 91125, USA
²⁴ Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia
²⁵ Universität-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany

Received: 14 November 2013
Accepted: 31 January 2015

Abstract

Aims. We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S).

Methods. Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search for extended X-ray emission down to an unprecedented flux of 2 × 10^-16 ergs s^-1 cm^-2. By using simulations and comparing them with the Chandra and XMM data, we show that it is feasible to probe extended sources of this flux level, which is 10 000 times fainter than the first X-ray group catalogs of the ROSAT all sky survey. Extensive spectroscopic surveys at the VLT and Magellan have been completed, providing spectroscopic identification of galaxy groups to high redshifts. Furthermore, available HST imaging enables a weak-lensing calibration of the group masses.

Results. We present the search for the extended emission on spatial scales of 32′′ in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDF-S, such as log  N − log  S and X-ray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/dΩ test reveals that a redshift range of 0.2 < z < 0.5 in ECDF-S is sparsely populated. The lack of nearby structure, however, makes studies of high-redshift groups particularly easier both in X-rays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weak-lensing analysis to show that the detected low-luminosity systems are indeed low-mass systems. We verify the applicability of the scaling relations between the X-ray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDF-S by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30% in mass.

Conclusions. Ultra-deep X-ray surveys uniquely probe the low-mass galaxy groups across a broad range of redshifts. These groups constitute the most common environment for galaxy evolution. Together with the exquisite data set available in the best studied part of the Universe, the ECDF-S group catalog presented here has an exceptional legacy value.