1,079 research outputs found
Superdense and normal early-type galaxies at 1<z<2
We combined proprietary and archival HST observations to collect a sample of
62 early-type galaxies (ETGs) at 0.9<z<2 with spectroscopic confirmation of
their redshift and spectral type. The whole sample is covered by ACS or NICMOS
observations and partially by Spitzer and AKARI observations. We derived
morphological parameters by fitting their HST light profiles and physical
parameters by fitting their spectral energy distributions. The study of the
size-mass and the size-luminosity relations of these early-types shows that a
large fraction of them (~50) follows the local relations. These 'normal' ETGs
are not smaller than local counterparts with comparable mass. The remaining
half of the sample is composed of compact ETGs with sizes (densities) 2.5-3
(15-30) times smaller (higher) than local counterparts and, most importantly,
than the other normal ETGs at the same redshift and with the same stellar mass.
This suggests that normal and superdense ETGs at z~2 come from different
histories of mass assembly.Comment: 4 pages, 3 figures. To appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and
C.C. Popescu, AIP Conf. (in press
Validation of fluorescence transition probability calculations
A systematic and quantitative validation of the K and L shell X-ray
transition probability calculations according to different theoretical methods
has been performed against experimental data. This study is relevant to the
optimization of data libraries used by software systems, namely Monte Carlo
codes, dealing with X-ray fluorescence. The results support the adoption of
transition probabilities calculated according to the Hartree-Fock approach,
which manifest better agreement with experimental measurements than
calculations based on the Hartree-Slater method.Comment: 8 pages, 21 figures and images, 3 tables, to appear in proceedings of
the Nuclear Science Symposium and Medical Imaging Conference 2009, Orland
Kinetics of self-induced aggregation in Brownian particles
We study a model of interacting random walkers that proposes a simple
mechanism for the emergence of cooperation in group of individuals. Each
individual, represented by a Brownian particle, experiences an interaction
produced by the local unbalance in the spatial distribution of the other
individuals. This interaction results in a nonlinear velocity driving the
particle trajectories in the direction of the nearest more crowded regions; the
competition among different aggregating centers generates nontrivial dynamical
regimes. Our simulations show that for sufficiently low randomness, the system
evolves through a coalescence behavior characterized by clusters of particles
growing with a power law in time. In addition, the typical scaling properties
of the general theory of stochastic aggregation processes are verified.Comment: RevTeX, 9 pages, 9 eps-figure
Cluster and field elliptical galaxies at z~1.3. The marginal role of the environment and the relevance of the galaxy central regions
We compared the properties of 56 elliptical galaxies selected from three
clusters at with those of field galaxies in the GOODS-S (~30),
COSMOS (~180) and CANDELS (~220) fields. We studied the relationships among
effective radius, surface brightness, stellar mass, stellar mass density
and central mass density within 1 kpc radius. We
find that cluster ellipticals do not differ from field ellipticals: they share
the same structural parameters at fixed mass and the same scaling relations. On
the other hand, the population of field ellipticals at shows a
significant lack of massive ( M) and large (R kpc) ellipticals with respect to the cluster. Nonetheless, at
M, the two populations are similar. The size-mass
relation of ellipticals at z~1.3 defines two different regimes, above and below
a transition mass M: at lower masses the
relation is nearly flat (R), the mean radius is
constant at ~1 kpc and while, at larger masses,
the relation is R. The transition mass marks the
mass at which galaxies reach the maximum . Also the
-mass relation follows two different regimes,
, defining a transition mass
density M pc. The mass density
does not correlate with mass, dense/compact galaxies can be
assembled over a wide mass regime, independently of the environment. The
central mass density, , besides to be correlated with the mass,
is correlated to the age of the stellar population: the higher the central
stellar mass density, the higher the mass, the older the age of the stellar
population. [Abridged]Comment: Accepted for publication in A&A; 20 pages, 13 figures (replaced to
match the A&A version
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