Surface density of extremely red objects with R - J ≥ 5

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 and J band magnitudes more than 10σ above background (). Thirty five of these objects have been detected in both J and R-band. We derive a surface density for such EROs of  arcmin^-2, which is about seven times lower than for galaxies with . Stellar population models suggest that these EROs are massive galaxies with an old stellar population in a redshift range of . For this scenario, we estimate the co-moving volume density to be ( Mpc^-3.