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

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 deg 2 , consisting of 50 single fields, each approximately 210 arcmin 2 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 σ 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 .