Surface density of extremely red objects with R - J 5

Free access article

Issue		A&A Volume 443, Number 3, December I 2005


Page(s)		831 - 839
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20042208

A&A 443, 831-839 (2005)
DOI: 10.1051/0004-6361:20042208

Surface density of extremely red objects with R - J $\geq$ 5

A. Hempel^{1, 2}, T. M. Herbst² and D. J. Thompson^{2, 3}

¹ Geneva Observatory, 51 Ch. des Maillettes, Sauverny 1290, Switzerland
    e-mail: Angela.Hempel@obs.unige.ch
² Max Planck Institute for Astronomy (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
    e-mail: herbst@mpia.de
³ The Palomar Observatory, California Institute of Technology, Pasadena, CA 91125, USA
    e-mail: djt@irastro.caltech.edu

(Received 19 October 2004 / Accepted 5 April 2005 )

Abstract
We present the results of a wide-field survey for extremely red objects (EROs), based on J and R band imaging. The survey covers 2.89 deg², consisting of 50 single fields, each approximately 210 arcmin² in size. This survey provides a sample of 60 extended objects with a colour of $R-J \ge 5$ and J band magnitudes more than 10 $\sigma$ above background ( $18^{\rm mag}\le J \le 20^{\rm mag}$ ). Thirty five of these objects have been detected in both J and R-band. We derive a surface density for such EROs of $5.7\pm0.1\times10^{-3}$ arcmin^-2, which is about seven times lower than for galaxies with $R-K\ge6$ . Stellar population models suggest that these EROs are massive galaxies with an old stellar population in a redshift range of $1.4\le z \le 3.0$ . For this scenario, we estimate the co-moving volume density to be ( $9.57 \pm 1.24) \times10^{-6}$ Mpc^-3.

Key words: Galaxy: evolution -- galaxies: high-redshift -- galaxies: elliptical and lenticular, cD

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