Involved people at OAB: Pozzetti, Zamorani.
A project aimed at studying the nature of the Extremely Red Galaxies (ERGs)
has been initiated in collaboration with Arcetri Observatory.
From near-IR (ESO 2.2m+IRAC2) and optical (NTT + EMMI SUSI, HST+WFPC2)
imaging data we have selected several ERGs
(R-K>6 and/or I-K>5) both in ``empty'' fields
(Pozzetti et al. in preparation) and around
radio-loud AGNs at 
(Cimatti et al. 1999).
Most of the HST morphologies of the red selected objects look regular and
compact, and only few objects are diffuse or strongly disturbed.
The comparison of the observed surface density and color distribution
with the predictions from a ``monolithic collapse'' model shows a deficit
of passively evolving ellipticals formed at z>5.
The contamination of the ERG sample by dust-reddened starbursts and/or
AGN has been investigated through near-infrared spectroscopy in order to
search for emission lines (e.g. H
) redshifted in the 1-2.4
m
region. A sample of 9 ERGs with R-K>5 and 
was observed with
the ESO VLT-UT1 equipped with ISAAC. Neither strong emission lines
(
erg s
cm
) nor continuum breaks
were detected. 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 z>0.8 (Cimatti et al. 1999).