Astronomy & Astrophysics

Free access article

Issue		A&A Volume 392, Number 2, September III 2002
Page(s)		395 - 406
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20020861

A&A 392, 395-406 (2002)
DOI: 10.1051/0004-6361:20020861

The K20 survey

III. Photometric and spectroscopic properties of the sample

A. Cimatti¹, M. Mignoli², E. Daddi³, L. Pozzetti², A. Fontana⁴, P. Saracco⁵, F. Poli⁶, A. Renzini³, G. Zamorani², T. Broadhurst⁷, S. Cristiani^{8, 9}, S. D'Odorico³, E. Giallongo⁴, R. Gilmozzi³ and N. Menci⁴

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

(Received 5 April 2002 / Accepted 6 June 2002 )

Abstract
The K20 survey is an ESO VLT optical and near-infrared spectroscopic survey aimed at obtaining spectral information and redshifts of a complete sample of about 550 objects to $K_{\rm s}\leq20.0$ over two independent fields with a total area of 52 arcmin ². In this paper we discuss the scientific motivation of such a survey, we describe the photometric and spectroscopic properties of the sample, and we release the $K_{\rm s}$ -band photometric catalog. Extensive simulations showed that the sample is photometrically highly complete to $K_{\rm s}=20$ . The observed galaxy counts and the $R-K_{\rm s}$ color distribution are consistent with literature results. We observed spectroscopically 94% of the sample, reaching a spectroscopic redshift identification completeness of 92% to $K_{\rm s}\leq20.0$ for the observed targets, and of 87% for the whole sample (i.e. counting also the unobserved targets). Deep spectroscopy was complemented with multi-band deep imaging in order to derive tested and reliable photometric redshifts for the galaxies lacking spectroscopic redshifts. The results show a very good agreement between the spectroscopic and the photometric redshifts with ${<z_{\rm spe}-z_{\rm phot}>}=0.01$ and with a dispersion of $\sigma_{\Delta z}=0.09$ . Using both the spectroscopic and the photometric redshifts, we reached an overall redshift completeness of about 98%. The size of the sample, the redshift completeness, the availability of high quality photometric redshifts and multicolor spectral energy distributions make the K20 survey database one of the most complete samples available to date for constraining the currently competing scenarios of galaxy formation and for a variety of other galaxy evolution studies.

Key words: galaxies: evolution; galaxies: formation

Offprint request: A. Cimatti, cimatti@arcetri.astro.it

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