Free Access
Volume 376, Number 3, September IV 2001
Page(s) 825 - 836
Section Extragalactic astronomy

A&A 376, 825-836 (2001)
DOI: 10.1051/0004-6361:20011029

The spatial clustering of distant, $z\sim1$, early-type galaxies

E. Daddi1, T. Broadhurst2, G. Zamorani3, A. Cimatti4, H. Röttgering5 and A. Renzini2

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

(Received 18 April 2001 / Accepted 10 July 2001 )

We examine the spatial clustering of extremely red objects (EROs) found in a relatively large survey of 700 arcmin2, containing 400 galaxies with $R-K{\rm s}> 5$ to $K{\rm s}=19.2$. A comoving correlation length $r_0=12\pm3$ h-1 Mpc is derived, under the assumption that the selection function is described by a passively evolving early-type galaxy population, with an effective redshift of $z\sim 1.2$. This correlation length is very similar to that of local L* elliptical galaxies implying, at face value, no significant clustering evolution in comoving coordinates of early-type galaxies to the limiting depth of our sample, $z\sim1.5$. A rapidly evolving clustering bias can be designed to reproduce a null result; however, our data do not show the corresponding strong reduction in the average population density expected for consistency with underlying growth of the mass-function. We discuss our data in the context of recent ideas regarding bias evolution. The uncertainty we quote on r0 accounts for the spikey redshift distribution expected along relatively narrow sightlines, which we quantify with detailed simulations. This is an improvement over the standard use of Limber's equation which, because of its implicit assumption of a smooth selection function, underestimates the true noise by a factor of $\approx$3 for the parameters of our survey. We propose a general recipe for the analysis of angular clustering, suggesting that any measurement of the angular clustering amplitude, A, has an intrinsic additional uncertainty of $\sigma_A/A=\sqrt{AC}$, where AC is the appropriate integral constraint.

Key words: cosmology: large-scale structure of Universe -- galaxies: evolution -- galaxies: elliptical and lenticular, cD -- galaxies: formation -- galaxies: fundamental parameters

Offprint request: E. Daddi,

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