The K20 survey. I. Disentangling old and dusty star-forming galaxies in the ERO population

2001/11/28 by A. Cimatti, E. Daddi, M. Mignoli +14 · 30 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph

paper · pdf · doi:10.1051/0004-6361:20011696

5 pages, 3 figures, to appear in Astronomy & Astrophysics Letters

arxiv created 2001/11/28 · openalex publication_date 2002/01/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31

Abstract

We present the results of VLT optical spectroscopy of a complete sample of 78 EROs with R-Ks≥5 over a field of 52 arcmin². About 70% of the 45 EROs with Ks≤19.2 have been spectroscopically identified with old passively evolving and dusty star-forming galaxies at 0.7<z<1.5. The two classes are about equally populated and for each of them we present and discuss the average spectrum. From the old ERO average spectrum and for Z=Z_\odot we derive a minimum age of ∼ 3 Gyr, corresponding to a formation redshift of z_f \gtsima 2.4. PLE models with such formation redshifts well reproduce the density of old EROs (consistent with being passively evolving ellipticals), whereas the predictions of the current hierarchical merging models are lower than the observed densities by large factors (up to an order of magnitude). From the average spectrum of the star-forming EROs we estimate a substantial dust extinction with E(B-V) \gtsima 0.5. The star formation rates, corrected for the average reddening, suggest a significant contribution from EROs to the cosmic star-formation density at z ∼ 1.

Citations

• Star Formation in Galaxies Along the Hubble Sequence

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