4,926 research outputs found
The role of homophily in the emergence of opinion controversies
Understanding the emergence of strong controversial issues in modern
societies is a key issue in opinion studies. A commonly diffused idea is the
fact that the increasing of homophily in social networks, due to the modern
ICT, can be a driving force for opinion polariation. In this paper we address
the problem with a modelling approach following three basic steps. We first
introduce a network morphogenesis model to reconstruct network structures where
homophily can be tuned with a parameter. We show that as homophily increases
the emergence of marked topological community structures in the networks
raises. Secondly, we perform an opinion dynamics process on homophily dependent
networks and we show that, contrary to the common idea, homophily helps
consensus formation. Finally, we introduce a tunable external media pressure
and we show that, actually, the combination of homophily and media makes the
media effect less effective and leads to strongly polarized opinion clusters.Comment: 24 pages, 10 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
Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies at z ~ 1.4
This paper aims at understanding if the normalization of the stellar initial
mass function (IMF) of massive early-type galaxies (ETGs) varies with cosmic
time and/or with mean stellar mass density Sigma (M*/2\pi Re^2). For this
purpose we collected a sample of 18 dense (Sigma>2500 M_sun/pc^2) ETGs at
1.2<z<1.6 with available velocity dispersion sigma_e. We have constrained their
mass-normalization by comparing their true stellar masses (M_true) derived
through virial theorem, hence IMF independent, with those inferred through the
fit of the photometry assuming a reference IMF (M_ref). Adopting the virial
estimator as proxy of the true stellar mass, we have assumed for these ETGs
zero dark matter (DM). However, dynamical models and numerical simulations of
galaxy evolution have shown that the DM fraction within Re in dense high-z ETGs
is negligible. We have considered the possible bias of virial theorem in
recovering the total masses and have shown that for dense ETGs the virial
masses are in agreement with those derived through more sophisticated dynamical
models. The variation of the parameter Gamma = M_true/M_ref with sigma_e shows
that, on average, dense ETGs at = 1.4 follow the same IMF-sigma_e trend of
typical local ETGs, but with a lower mass-normalization. Nonetheless, once the
IMF-sigma_e trend we have found for high-z dense ETGs is compared with that of
local ETGs with similar Sigma and sigma_e, they turn out to be consistent. The
similarity between the IMF-sigma_e trends of dense high-z and low-z ETGs over 9
Gyr of evolution and their lower mass-normalization with respect to the mean
value of local ETGs suggest that, independently on formation redshift, the
physical conditions characterizing the formation of a dense spheroid lead to a
mass spectrum of new formed stars with an higher ratio of high- to low-mass
stars with respect to the IMF of normal local ETGs.Comment: 9 pages, 4 figures, accepted for pubblication in A&A, updated to
match final journal versio
Age, metallicity and star formation history of spheroidal galaxies in cluster at z~1.2
We present the analysis, based on spectra collected at the Large Binocular
Telescope, of the stellar populations in seven spheroidal galaxies in the
cluster XLSSJ0223 at 1.22. The aim is to constrain the epoch of their
formation and their star formation history. Using absorption line strenghts and
full spectral fitting, we derive for the stellar populations of the seven
spheroids a median age =2.40.6 Gyr, corresponding to a median
formation redshift $\sim2.6_{-0.5}^{+0.7}$ (lookback time =
11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that
massive spheroids, at least in our targeted cluster, are not coeval. The median
metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at
0$<z<<\sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_ez\sim1.3$, i.e.
more massive spheroids are more metal rich, have lower stellar mass density and
tend to be older than lower-mass galaxies.Comment: 16 pages, 6 figures, 6 tables, published on MNRA
The population of early-type galaxies: how it evolves with time and how it differs from passive and late-type galaxies
The aim of our analysis is twofold. On the one hand we are interested in
addressing whether a sample of ETGs morphologically selected differs from a
sample of passive galaxies in terms of galaxy statistics. On the other hand we
study how the relative abundance of galaxies, the number density and the
stellar mass density for different morphological types change over the redshift
range 0.6<z<2.5. From the 1302 galaxies brighter than Ks=22 selected from the
GOODS-MUSIC catalogue, we classified the ETGs on the basis of their morphology
and the passive galaxies on the basis of their sSFR. We proved how the
definition of passive galaxy depends on the IMF adopted in the models and on
the assumed sSFR threshold. We find that ETGs cannot be distinguished from the
other morphological classes on the basis of their low sSFR, irrespective of the
IMF adopted in the models. Using the sample of 1302 galaxies morphologically
classified into spheroidal galaxies (ETGs) and not spheroidal galaxies (LTGs),
we find that their fractions are constant over the redshift range 0.6<z<2.5
(20-30% ETGs vs 70-80% LTGs). However, at z<1 these fractions change among the
population of the most massive (M*>=10^(11) M_sol) galaxies, with the fraction
of massive ETGs rising up to 40% and the fraction of massive LTGs decreasing
down to 60%. Moreover, we find that the number density and the stellar mass
density of the whole population of massive galaxies increase almost by a factor
of ~10 between 0.6<z<2.5, with a faster increase of these densities for the
ETGs than for the LTGs. Finally, we find that the number density of the
highest-mass galaxies (M*>3-4x10^(11) M_sol) both ETGs and LTGs do not increase
since z~2.5, contrary to the lower mass galaxies. This suggests that the
population of the most massive galaxies formed at z>2.5-3 and that the assembly
of such high-mass galaxies is not effective at lower redshift.Comment: 15 pages, 14 figures. Published in A&
Electronic transport within a quasi two-dimensional model for rubrene single-crystal field effect transistors
Spectral and transport properties of the quasi two-dimensional adiabatic
Su-Schrieffer-Heeger model are studied adjusting the parameters in order to
model rubrene single-crystal field effect transistors with small but finite
density of injected charge carriers. We show that, with increasing temperature
, the chemical potential moves into the tail of the density of states
corresponding to localized states, but this is not enough to drive the system
into an insulating state. The mobility along different crystallographic
directions is calculated including vertex corrections which give rise to a
transport lifetime one order of magnitude smaller than spectral lifetime of the
states involved in the transport mechanism. With increasing temperature, the
transport properties reach the Ioffe-Regel limit which is ascribed to less and
less appreciable contribution of itinerant states to the conduction process.
The model provides features of the mobility in close agreement with
experiments: right order of magnitude, scaling as a power law ,
with close or larger than two, and correct anisotropy ratio between
different in-plane directions. Due to a realistic high dimensional model, the
results are not biased by uncontrolled approximations.Comment: 10 pages, 9 figures, Submitte
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