Introduction

Extremely Red Objects

Extremely Red Objects (EROs) are variously defined in the literature. They appear to be comprised of two separate populations -- dusty, star-forming galaxies (e.g., HR 10) and passively-evolving ellipticals (e.g., LBDS 53W091). The surface density of EROs on the sky is quite uncertain, since the objects are known to be strongly clustered. However, published numbers suggest that we will find one object every few square arcminutes with K<19 and R-K>5. At these bright magnitudes, optical spectroscopy should be successful in measuring redshifts for at least the former class of object, which are expected to show strong [O II] 3727 emission. Since the two classes of object are likely to display different clustering characteristics, the ability to identify to which class an individual object belongs is very important, even if we cannot determine spectroscopic redshifts for objects in the latter class. Pozzetti & Manucci (2000) suggested that they can be separated into two groups by comparing their optical to near infrared colors (I-J and J-K) and we can test this with spectroscopy.

The deep near-infrared UKIRT/WFCAM data which we hope to obtain will allow us to study the luminosity function of EROs to depths never before determine. Optical data to R=28 is necessary to properly compare with the K=23 galaxy population.