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Astron. Astrophys. 352, L45-L50 (1999)

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Letter to the Editor

New clues on the nature of extremely red galaxies *

A. Cimatti 1, E. Daddi 2, S. di Serego Alighieri 1, L. Pozzetti 1, F. Mannucci 3, A. Renzini 4, E. Oliva 1, G. Zamorani 5, P. Andreani 6 and H.J.A. Röttgering 7

1 Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy (cimatti@arcetri.astro.it)
2 Università di Firenze, Dipartimento di Astronomia, Largo Fermi 5, 50125 Firenze, Italy
3 CAISMI-CNR, Largo Fermi 5, 50125 Firenze, Italy
4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
5 Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6 Osservatorio Astronomico di Padova, vicolo dell' Osservatorio 5, 35122 Padova, Italy
7 Sterrewacht Leiden, Sterrewacht, Postbus 9513, Leiden 2300 RA, The Netherlands

Received 17 August 1999 / Accepted 19 September 1999


We present near-infrared VLT-UT1+ISAAC spectroscopy of a sample of 9 extremely red galaxies (ERGs) with [FORMULA] and [FORMULA]. Neither strong emission lines ([FORMULA]1-5[FORMULA] erg s- 1 cm-2) nor continuum breaks are detected. From near-infrared spectrophotometry, complemented with broad-band optical and near-IR photometry, we estimate "spectro-photometric" redshifts to be in the range of [FORMULA]. We derive upper limits on the star formation rates in range of [FORMULA]. Two of the observed ERGs are dusty starburst candidates because they require strong dust reddening to reproduce their global spectral energy distributions. The other ERGs are consistent with being dustless old passively evolved spheroidals at [FORMULA]. We discuss the general implications of our findings in relation with the problem of the formation of early type galaxies.

Key words: galaxies: evolution – galaxies: formation – galaxies: general

* Based on observations made at the European Southern Observatory, La Silla and Paranal, Chile

Send offprint requests to: A. Cimatti

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999