Number counts of bright extremely red objects: Evolved massive galaxies at z 

¹ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile
² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³ Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
⁴ Observatory, PO Box 14, 00014 University of Helsinki, Finland

Corresponding author: P. Väisänen, pvaisane@eso.org

Received: 10 December 2003
Accepted: 8 April 2004

Abstract

We present results on number counts of Extremely Red Objects (EROs) in a 2850 arcmin² near-infrared survey performed in European Large Area ISO Survey (ELAIS) fields at . Counts of EROs are extended to brighter levels than available previously, giving at and consistent numbers with literature values at fainter magnitudes. Photometric redshifts from HYPERZ as well as GRASIL model SEDs of galaxies imply that our EROs are located in the range , with the bulk of the population at . Taking advantage of the ISO data in the fields, we use mid-IR detections to constrain the number of dusty EROs, and also discuss the superior capabilities of Spitzer Space Telescope to detect dusty EROs. Both the mid-IR data and the use of colour-colour diagrammes indicate that at most 10-20% of the EROs in this bright regime are dusty starbursting systems. The space density of our EROs, interpreted to be counterparts of local massive galaxies at around , is estimated to be , which is consistent with local values. Furthermore, the cumulative number counts at our bright magnitudes are remarkably well fitted by pure luminosity evolution models.