| Abstract
| - We present results on number counts of Extremely Red Objects (EROs) in a 2850 arcmin 2 near-infrared survey performed in European Large Area ISO Survey (ELAIS) fields at $K<17.5$. Counts of EROs are extended to brighter levels than available previously, giving $0.002 \pm 0.001 \ \rm arcmin^{-2}$ at $K<16.5$ 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 $z=0.7{-}1.5$, with the bulk of the population at $z\sim1$. 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 ${>}2{-}3~L^{\star}$ massive galaxies at around $z\sim1$, is estimated to be ${\approx}2\times10^{-5} ~ {\rm Mpc^{-3}}$, which is consistent with local values. Furthermore, the cumulative number counts at our bright magnitudes are remarkably well fitted by pure luminosity evolution models.
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