Evolution of UV–NIR structural properties of cluster galaxies *,**
1
INAF, Istituto Nazionale di Astrofisica Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: labarber@na.astro.it
2
Università degli Studi di Trieste, Department of Astronomy, Trieste, Italy
Corresponding author: P. Merluzzi, merluzzi@na.astro.it
Received:
25
November
2002
Accepted:
19
May
2003
We study the structure and the internal colour gradients of
cluster galaxies from UV to NIR restframe, in the redshift range
. Structural parameters (half light radius
, mean surface brightness 
and Sersic
index 
) are derived for galaxies in the clusters 
at
and 
at 
. This data
set, together with previous data for the cluster 
at
, constitutes the first large (
) sample of cluster galaxies whose internal structure in UV,
optical (OPT) and NIR (U-, V- and H-band restframe) can be
investigated up to a look-back time of 
(
, 
and 
). Galaxies are classified as spheroids or
disks according to the shape of the light profile, and the evolution
of the two populations are investigated separately. On average,
both spheroids and disks are more concentrated at longer
wavelengths: the galaxy sizes become smaller from UV to NIR, while
Sersic indices increase. This trend shows an evolution in disks,
where the mean ratio of optical to NIR Sersic indices decreases from
to 
. Colour gradients are on
average negative at all redshifts and are stronger in disks than in
spheroids. But while for spheroids both 
and
are only weakly dependent on redshift, the
optical-NIR gradients of disks become significantly smaller at
. Colour gradients and central colours are compared
with models of metallicity, age, and dust extinction
gradients. Metallicity turns out to be the primary driver of colour
gradients in spheroids, the age gradient being constrained to be
smaller than 
. For disks, two kinds of models fit the
present data: (i) age gradients (in the range
[30, 50]%) with significant dust extinction, and (ii)
“pure” dust models, in which the gradients of colour excess are a
factor of two higher in than in the other clusters. Since
colour gradients of disks seem not to correlate significantly with
inclination, we argue that age gradient models could represent a
more likely explanation of the present data, in agreement with what
expected on the basis of hierarchical merging scenarios.
Key words: galaxies: clusters: individual: A 209, AC 118, EIS 0048 / galaxies: photometry / galaxies: evolution / galaxies: fundamental parameters (colours, colour gradients, effective radii, Sersic indices)
© ESO, 2003