Issue |
A&A
Volume 414, Number 1, January IV 2004
|
|
---|---|---|
Page(s) | 95 - 106 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20031608 | |
Published online | 12 January 2004 |
On the colour–colour properties of the Extremely Red Objects
1
Department of Astronomy and Astrophysics, Centre for Astrophysics and Space Science, Chalmers University of Technology, 439 92 Onsala, Sweden e-mail: stefan@oso.chalmers.se
2
European Space Agency, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: wiklind@stsci.edu
Corresponding author: S. Bergström, stefan@oso.chalmers.se
Received:
7
May
2003
Accepted:
10
October
2003
The colours of the galaxy class known as Extremely Red Objects
(EROs; ) are considered to be consistent with two distinct galaxy
populations at high redshift: evolved ellipticals or young dusty
starbursts. In this paper the properties of EROs, spanned by the
five photometric bands RIJHK, are investigated as to the
possibility to distinguish between these two galaxy populations
using only broad band photometry. The broad band colours of
elliptical and starburst galaxies at redshifts up to 5 are computed from
synthetic spectra obtained using the spectral evolution synthesis programme
PÉGASE.2. Two initial mass functions and a range of metallicities and
extinctions are used. In order to be extremely red in the redshift range
considered, the evolution of the
colour sets the requirement that
ellipticals have to be less than
Gyr old, and that the starbursts
must have colour excesses of
, as derived from the nebular
emission lines. In investigating the overlap in the different colour–colour
planes as a function of redshift, it is found that the planes formed from
permutations of the same three filters exhibit very similar overlap
characteristics. In colour–colour planes formed within such triplets one of the
filters will serve as a “pivot” band against which the two other bands are
compared. The configuration where this pivot band lies between the other two
bands has the best performance as a discriminator among the three possible
configurations. A consistent behaviour cannot be found among the
configurations formed by permuting four filters. The minimal filter
configuration
vs.
is found to be the very best discriminator,
working as such up to redshift 2.9.
Key words: galaxies: elliptical and lenticular, cD / galaxies: evolution / galaxies: fundamental parameters / galaxies: high-redshift / galaxies: starburst
© ESO, 2004
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