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Astron. Astrophys. 361, 535-549 (2000)

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Detection of strong clustering of extremely red objects: implications for the density of z [FORMULA] 1 ellipticals *

E. Daddi 1, A. Cimatti 2, L. Pozzetti 2,3, H. Hoekstra 4, H.J.A. Röttgering 5, A. Renzini 6, G. Zamorani 3 and F. Mannucci 7

1 Università degli Studi di Firenze, Dipartimento di Astronomia e Scienza dello Spazio, Largo E. Fermi 5, 50125 Firenze, Italy
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3 Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
4 Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands
5 Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
6 European Southern Observatory, 85748 Garching, Germany
7 CAISMI-CNR, Largo E. Fermi 5, 50125 Firenze, Italy

Received 18 May 2000 / Accepted 7 August 2000


We present the results of a wide-field survey for extremely red objects (EROs hereafter), the widest so far, based on Ks and R band imaging. The survey covers 701 arcmin2 and it is 85% complete to [FORMULA] over the whole area and to [FORMULA] over 447.5 arcmin2. Thanks to the wide field covered, a complete sample of about 400 EROs with [FORMULA]5 was selected. The distribution of the EROs on the sky is strongly inhomogeneous, being characterized by overdensities and large voids. We detect at the [FORMULA] level a strong clustering signal of the EROs which is about an order of magnitude larger than the clustering of K-selected field galaxies in the same magnitude range. A smooth trend of increasing clustering amplitude with the [FORMULA] color is observed. These results are strong evidence that the largest fraction of EROs is composed of high-z ellipticals, of which we detect for the first time the [FORMULA] large scale structure clustering signal. We show how the surface density variations of the ERO population found in our survey can explain the highly discrepant results obtained so far on the density of [FORMULA] ellipticals, and we briefly discuss the main implications of our results for the evolution of elliptical galaxies. The number counts and the colors of the K-selected field galaxies are also presented and briefly discussed.

Key words: galaxies: elliptical and lenticular, cD – galaxies: evolution – galaxies: formation – galaxies: starburst – cosmology: large-scale structure of Universe – galaxies: clusters: general

* Partially based on observations made at the European Southern Observatory in La Silla, Chile.

Send offprint requests to: edaddi@arcetri.astro.it

© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000