A VLT/FORS2 spectroscopic survey in the HDF-S

E. Vanzella , S. Cristiani , S. Arnouts , M. Dennefeld (1) , A. Fontana , A. Grazian , M. Nonino , P. Petitjean (1) , P. Saracco

1 IAP - Institut d'Astrophysique de Paris

We report on low-resolution multi-object spectroscopy of 65 objects from I(AB) ~= 20 to I(AB) ~= 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 =~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 ~= 2.1 and z ~= 2.7 and a pronounced low redshift peak around z ~= 0.58. An elliptical galaxy lensing a background object turns out to be at a redshift z=0.577.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]

E. Vanzella, S. Cristiani, S. Arnouts, M. Dennefeld, A. Fontana, et al.. A VLT/FORS2 spectroscopic survey in the HDF-S. Astronomy and Astrophysics - A&A, 2002, 396, pp.847-856. ⟨hal-00005611⟩