EDP Sciences
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Volume 398, Number 1, January IV 2003
Page(s) 127 - 132
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20021696

A&A 398, 127-132 (2003)
DOI: 10.1051/0004-6361:20021696

Massive $z\sim1.3$ evolved galaxies revealed

P. Saracco1, M. Longhetti1, P. Severgnini1, R. Della Ceca1, F. Mannucci2, R. Bender3, N. Drory4, G. Feulner3, F. Ghinassi5, U. Hopp3 and C. Maraston3

1  INAF - Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
    e-mail: [saracco, marcella]@merate.mi.astro.it; [paola, rdc]@brera.mi.astro.it
2  IRA-CNR, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: filippo@arcetri.astro.it
3  Universitäts-Sternwarte München, Scheiner Str. 1, 81679 München, Germany
    e-mail: [bender, feulner, hopp, maraston]@usm.uni-muenchen.de
4  University of Texas at Austin, Austin, Texas 78712, USA
    e-mail: drory@astro.as.utexas.edu
5  Centro Galileo Galilei, La Palma, Spain
    e-mail: ghinassi@tng.iac.es

(Received 19 September 2002 / Accepted 8 November 2002 )

We present the results of TNG near-IR low resolution spectroscopy of two (S7F5_254 and S7F5_45) sources belonging to a complete sample of 15 EROs with K'  <18 and R-K'  >5 selected from the MUNICS Survey. Both the spectra show a sharp drop in the continuum which can be ascribed only to the Balmer break. This places them at 1.2  <z<1.5. Their rest-frame z=1.2 K-band absolute magnitude is $M_K\simeq-26.6$ ( L  $\sim7L^*$). The comparison of the spectra and the photometric data with a grid of synthetic template spectra provides a redshift $z\simeq1.22^{-0.07}_{+0.2}$ for S7F5_254 and $z\simeq1.46\pm0.02$ for S7F5_45. The resulting lower limits to their stellar mass are $\mathcal{M}_{{\rm stars}}^{{\rm min}}=6\times10^{11}~M_\odot$ and $\mathcal{M}_{{\rm stars}}^{{\rm min}}=4\times10^{11}~M_\odot$. The minimum age of the last burst of star formation in S7F5_254 is 3.5 Gyr while it is 0.5 Gyr in S7F5_45 implying a minimum formation redshift $z_{\rm f}\ga3.5$ and $z_{\rm f}\ga2$ for the two EROs respectively.

Key words: galaxies: evolution -- galaxies: elliptical and lenticular, cD -- galaxies: formation

Offprint request: P. Saracco, saracco@merate.mi.astro.it

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© ESO 2003