Bibcode
Franceschini, A.; Rodighiero, G.; Cassata, P.; Berta, S.; Vaccari, M.; Nonino, M.; Vanzella, E.; Hatziminaoglou, E.; Antichi, J.; Cristiani, S.
Bibliographical reference
Astronomy and Astrophysics, Volume 453, Issue 2, July II 2006, pp.397-421
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7
2006
Journal
Citations
89
Refereed citations
83
Description
Aims.We constrain the evolution of the galaxy mass and luminosity
functions from the analysis of (public) multi-wavelength data in the
Chandra Deep Field South (CDFS) area, obtained from GOODS and other
projects, including very deep high-resolution imaging by HST/ACS.Methods.Our reference catalogue of faint high-redshift galaxies, which
we have thoroughly tested for completeness and reliability, comes from a
deep (S3.6≥ 1 μJy) image by IRAC on the Spitzer
Observatory. These imaging data in the field are complemented by
extensive optical spectroscopy by the ESO VLT/FORS2 and VIMOS
spectrographs, while deep K-band VLT/ISAAC imaging is also used to
derive further complementary statistical constraints and to assist the
source identification and Spectral Energy Distribution (SED) analysis.
We selected a highly reliable IRAC 3.6 μm sub-sample of 1478 galaxies
with S3.6≥ 10 μJy, 47% of which have spectroscopic
redshift, while for the remaining objects we used both COMBO-17 data
(Wolf et al. 2004, A&A, 421, 913) and the code Hyperz (Bolzonella et
al. 2000, A&A, 363, 476) to estimate the photometric redshift. This
very extensive dataset was exploited to assess evolutionary effects in
the galaxy luminosity and stellar mass functions, while
luminosity/density evolution is further constrained with the number
counts and redshift distributions. The deep ACS imaging allows us to
differentiate between these evolutionary paths by morphological type,
which our simulations show to be reliable at least up to z˜ 1.5
for the two main early- (E/S0) and late-type (Sp/Irr) classes.Results.These data, as well as our direct estimate of the stellar mass
function above M_ast h^2=1010 M_&sun; for the spheroidal
subclass, consistently show a progressive dearth of such objects
starting at z˜ 0.7, paralleled by an increase in luminosity. A
similar trend, with a more modest decrease in the mass function, is also
shared by spiral galaxies, while the irregulars/mergers show an
increased incidence at higher z. Remarkably, this decrease in the
comoving density with redshift of the total population appears to depend
on galaxy mass, being stronger for moderate-mass galaxies, but almost
absent until z=1.4 for high-mass galaxies, thus confirming previous
evidence of a “downsizing” effect in galaxy formation.Conclusions.Our favoured interpretation of the evolutionary trends for
the two galaxy categories is that of a progressive morphological
transformation (due to gas exhaustion and, likely, merging) from the
star-forming to the passively evolving phase, starting at z≥ 2 and
holding on down to z˜ 0.7. The rate of this process appears to
depend on galaxy mass, being already largely settled by z˜ 1 for
the most massive systems.