Volume 501, Number 2, July II 2009
|Page(s)||485 - 494|
|Published online||19 May 2009|
On the nature of red galaxies: the Chandra perspective*
Max-Planck-Institut für Astrophysik (MPA), Karl-Schwarzschild-Str. 1, Garching b. Muenchen, 85748, Germany e-mail: firstname.lastname@example.org
2 Dipartimento di Astronomia, Università degli Studi di Bologna, via Ranzani 1, Bologna, Italy
3 INAF - Osservatorio Astronomico di Bologna, via Ranzani, 1, 40127 Bologna, Italy
4 Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany
5 Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, DAPNIA/SAP, Orme des Merisiers, 91191 Gif-sur-Yvette, France
6 Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
7 INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
8 National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
9 The Graduate University for Advanced Studies, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
10 Center for Astrophysics, University of Science and Technology of China, Hefei 230026, P.R. China
Accepted: 17 April 2009
We present the X-ray properties of the extremely red objects (ERO) population observed by Chandra with three partially overlapping pointings (up to ≈90 ks) over an area of ≈500 arcmin2, down to a 0.5–8 keV flux limit of ≈10-15 erg cm-2 s-1. We selected EROs using a multi-band photometric catalog down to a KS-band magnitude of ≈19.3 (Vega system); 14 EROs were detected in X-rays, corresponding to ≈9% of the overall X-ray source population (149 X-ray sources) and to ≈5% of the ERO population (288). The X-ray emission of all X-ray detected EROs is consistent with that of an active galactic nucleus (AGN) ( 3.51042 erg s-1 at photometric redshifts ), in agreement with previous X-ray observations, with an indication of increasing absorption between the three X-ray brightest EROs and the 11 X-ray faintest EROs. We take advantage of the good spatial resolution and limited background provided by Chandra to place constraints on the population of the X-ray undetected EROs by a stacking analysis. Their stacked emission, whose statistical significance is 5.7σ in the observed 0.5–8 keV band, provides an upper limit to the average intrinsic absorption at of 2.51022 cm-2 and corresponds to a rest-frame 0.5–8 keV luminosity of 8.91041 erg s-1. We estimate that any accretion-related X-ray emission to the stacked signal is likely “diluted” by emission due to hot gas in normal galaxies and star-formation activity in dust-enshrouded galaxies at high redshift.
Key words: galaxies: active / galaxies: nuclei / quasars: general / X-rays: galaxies
© ESO, 2009
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.