The K20 survey - II. The different spatial clustering of z similar to 1 old and dusty star-forming EROs

We compare the 3D clustering of old passively-evolving and dusty star-forming zsimilar to1 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 r(0) similar to 2.5 h(-1) Mpc. In contrast, the old EROs are much more positively correlated, with 5.5 less than or similar to r(0)/(h(-1) Mpc) less than or similar to 16, consistent with previous claims for zsimilar to1 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 r(0) for zsimilar to1 field early-type galaxies, but fail in matching their high number density and overall old ages.