631 research outputs found
Clustering at high redshift
The addition of deep near infrared images to the database provided by the
HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline
and address a number of key issues including the total stellar content of
baryonic mass, the effects of dust extinction, the dependence of morphology on
the rest frame wavelength, the photometric redshifts, the detection and nature
of extremely red objects (EROs). For these reasons deep near infrared images
were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks
bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A
multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the
HDF-S has been produced. Photometric redshifts have been generated both fitting
templates to the observed SEDs and with neural network techniques.
Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed
all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the
galaxies brighter than I_AB< 27.5 have been used to study the evolution of
galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies
at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A.
Renzini (ESO Astrophysics Symposia, Springer-Verlag
Irreversible phase transitions induced by an oscillatory input
A novel kind of irreversible phase transitions (IPT's) driven by an
oscillatory input parameter is studied by means of computer simulations. Second
order IPT's showing scale invariance in relevant dynamic critical properties
are found to belong to the universality class of directed percolation. In
contrast, the absence of universality is observed for first order IPT's.Comment: 18 pages (Revtex); 8 figures (.ps); submitted to Europhysics Letters,
December 9th, 199
The assembly of massive galaxies from NIR observations of the Hubble Deep Field South
We use a deep K(AB)<25 galaxy sample in the Hubble Deep Field South to trace
the evolution of the cosmological stellar mass density from z~ 0.5 to z~3. We
find clear evidence for a decrease of the average stellar mass density at high
redshift, 2<z<3.2, that is 15^{+25}_{-5}% of the local value, two times higher
than what observed in the Hubble Deep Field North. To take into account for the
selection effects, we define a homogeneous subsample of galaxies with
10^{10}M_\odot \leq M_* \leq 10^{11}M_\odot: in this sample, the mass density
at z>2 is 20^{+20}_{-5} % of the local value. In the mass--limited subsample at
z>2, the fraction of passively fading galaxies is at most 25%, although they
can contribute up to about 40% of the stellar mass density. On the other hand,
star--forming galaxies at z>2 form stars with an average specific rate at least
~4 x10^{-10} yr, 3 times higher than the z<~1 value. This
implies that UV bright star--forming galaxies are substancial contributors to
the rise of the stellar mass density with cosmic time. Although these results
are globally consistent with --CDM scenarios, the present rendition of
semi analytic models fails to match the stellar mass density produced by more
massive galaxies present at z>2.Comment: Accepted for publication on ApJLetter
High-z massive galaxies in the HDF-South
[abr] We report the analysis of three galaxies selected in the Hubble Deep
Field South at Ks3.
We have used population synthesis models to constrain their redshifts and their
stellar masses. One galaxy is at redshift z_p~2.4 while the other two are at
z_p~2.9-3.0. All three galaxies have already assembled a stellar mass of about
10^{11} M_sun at the observed redshift placing the possible merging event of
their formation at z>3.5. The inferred mass weighted age of their stellar
populations implies that the bulk of the stars formed at z_f>3.5. The resulting
co-moving density of M_{stars}>10^{11} M_sun galaxies at ~2.7 is
rho=1.2(+-0.7)x10^{-4} Mpc^{-3}, about a factor two higher than the predictions
of hierarchical models. The comparison with the local density of galaxies
implies that the three galaxies must have already formed most of their stellar
mass and that they cannot follow an evolution significantly different from a
passive aging.The comparison with the density of local L>L* early types
(passively evolved galaxies) suggests that their co-moving density cannot
decrease by more than a factor 2.5-3 from z=0 to z~3 and that up to 40% of the
stellar mass content of bright (L>L*) local early type galaxies was already in
place at z>2.5.Comment: 10 pages, 5 figures. Accepted for publication on A&
Characterization of PSII-LHCII supercomplexes isolated from pea thylakoid membranes by one-step treatment with α- and β- dodecyl-D-maltoside
The evolution of the galaxy luminosity function in the rest frame blue band up to z=3.5
We present an estimate of the cosmological evolution of the field galaxy
luminosity function (LF) in the rest frame 4400 Angstrom B -band up to redshift
z=3.5. To this purpose, we use a composite sample of 1541 I--selected galaxies
selected down to I_(AB)=27.2 and 138 galaxies selected down to K_(AB)=25 from
ground-based and HST multicolor surveys, most notably the new deep JHK images
in the Hubble Deep Field South (HDF-S) taken with the ISAAC instrument at the
ESO-VLT telescope. About 21% of the sample has spectroscopic redshifts, and the
remaining fraction well calibrated photometric redshifts. The resulting blue LF
shows little density evolution at the faint end with respect to the local
values, while at the bright end (M_B(AB)<-20) a brightening increasing with
redshift is apparent with respect to the local LF. Hierarchical CDM models
overpredict the number of faint galaxies by about a factor 3 at z=1. At the
bright end the predicted LFs are in reasonable agreement only at low and
intermediate redshifts (z=1), but fail to reproduce the pronounced brightening
observed in the high redshift (z=2-3) LF. This brightening could mark the epoch
where a major star formation activity is present in the galaxy evolution.Comment: 14 pages, 2 figures, Astrophysical Journal Letters, in pres
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