Letter to the Editor

The K20 survey^*

II. The different spatial clustering of old and dusty star-forming EROs

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
² Dipartimento di Astronomia, Università di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
³ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Racah Institute for Physics, The Hebrew University, Jerusalem 91904, Israel
⁵ Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ Osservatorio Astronomico di Brera, via E. Bianchi 46, Merate, Italy
⁷ Osservatorio Astronomico di Roma, via Dell'Osservatorio 2, Monteporzio, Italy
⁸ Dipartimento di Astronomia, Università “La Sapienza”, Roma, Italy
⁹ ST, European Coordinating Facility, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁰ Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy

Corresponding author: E. Daddi, edaddi@eso.org

Received: 21 December 2001
Accepted: 21 January 2002

Abstract

We compare the 3D clustering of old passively-evolving and dusty star-forming EROs from the K20 survey. With detailed simulations of clustering, the comoving correlation length of dusty star-forming EROs is constrained to be less than h^-1 Mpc. In contrast, the old EROs are much more positively correlated, with Mpc, consistent with previous claims for field early-type galaxies based on analyses of ERO angular clustering. The low level of clustering of dusty star-forming EROs does not support these to be major mergers building up an elliptical galaxy, or typical counterparts of SCUBA sources, but it is instead consistent with the weak clustering of high redshift blue galaxies and of luminous local IRAS galaxies. Current hierarchical merging models can explain the large r₀ for field early-type galaxies, but fail in matching their high number density and overall old ages.