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Issue A&A
Volume 396, Number 3, December IV 2002
Page(s) 847 - 855
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021453



A&A 396, 847-855 (2002)
DOI: 10.1051/0004-6361:20021453

A VLT/FORS2 spectroscopic survey in the HDF-S

E. Vanzella1, 2, S. Cristiani3, 4, S. Arnouts1, M. Dennefeld5, A. Fontana6, A. Grazian1, 2, M. Nonino3, P. Petitjean5 and P. Saracco7

1  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
2  Dipartimento di Astronomia dell'Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
3  INAF - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 40131 Trieste, Italy
4  Space Telescope European Coordinating Facility, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
5  Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
6  INAF - Osservatorio Astronomico di Roma, via dell'Osservatorio 2, Monteporzio, Italy
7  INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, Merate, Italy

(Received 21 June 2002 / Accepted 30 September 2002 )

Abstract
We report on low-resolution multi-object spectroscopy of 65 objects from $I(AB) \simeq 20$ to $I(AB) \simeq 25$ in the HDF-S obtained with the VLT Focal Reducer/low dispersion Spectrograph (FORS2). 18 objects belong to the HDF-S proper, i.e. the WFPC2 deep area. 15 high-redshift galaxies with 2.0 < z < 3.5 (10 in the HDF-S proper) have been identified. The spectroscopic redshifts are in good agreement with the photometric ones derived from a $\chi^{2}$ minimization technique comparing the observed spectral energy distribution with synthetic libraries and with a new neural network ( NN) approach. The dispersion with the former method is $\sigma_z=0.16$ whereas the latter provides $\sigma_z=0.13$. No "catastrophic" difference is encountered. The inferred star formation rates of the individual objects range from tens to a few hundreds of $M_{\odot}$ yr -1 and the global star formation rate of the Universe at $<z>\,\simeq 2.4$ is estimated to be 0.15 $M_{\odot}$ yr -1 Mpc -3 with a statistical error of 0.04.

Evidence for large-scale structure is found with two groups' redshifts observed at $z\simeq 2.1$ and $z\simeq 2.7$ and a pronounced low redshift peak around $z\simeq 0.58$.

An elliptical galaxy lensing a background object turns out to be at a redshift z=0.577.


Key words: techniques: spectroscopic -- galaxies: evolution -- galaxies: formation -- galaxies: distances and redshifts

Offprint request: E. Vanzella, evanzell@eso.org

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© ESO 2002

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