268 research outputs found
Weak Lensing Light-Cones in Modified Gravity simulations with and without Massive Neutrinos
We present a novel suite of cosmological N-body simulations called the
DUSTGRAIN-pathfinder, implementing simultaneously the effects of an extension
to General Relativity in the form of gravity and of a non-negligible
fraction of massive neutrinos. We describe the generation of simulated weak
lensing and cluster counts observables within a past light-cone extracted from
these simulations. The simulations have been performed by means of a
combination of the MG-GADGET code and a particle-based implementation of
massive neutrinos, while the light-cones have been generated using the MapSim
pipeline allowing us to compute weak lensing maps through a ray-tracing
algorithm for different values of the source plane redshift. The mock
observables extracted from our simulations will be employed for a series of
papers focussed on understanding and possibly breaking the well-known
observational degeneracy between gravity and massive neutrinos, i.e. the
fact that some specific combinations of the characteristic parameters for these
two phenomena (the scalar amplitude and the total neutrino mass
) may result indistinguishable from the standard
cosmology through several standard observational probes.
In particular, in the present work we show how a tomographic approach to weak
lensing statistics could allow - especially for the next generation of
wide-field surveys - to disentangle some of the models that appear
statistically indistinguishable through standard single-redshift weak lensing
probe.Comment: accepted for publication in MNRAS, added theoretical comparisons to
the simulation measurement
The mass-concentration relation in lensing clusters: the role of statistical biases and selection effects
The relation between mass and concentration of galaxy clusters traces their
formation and evolution. Massive lensing clusters were observed to be
over-concentrated and following a steep scaling in tension with predictions
from the concordance CDM paradigm. We critically revise the relation
in the CLASH, the SGAS, the LOCUSS, and the high-redshift samples of weak
lensing clusters. Measurements of mass and concentration are anti-correlated,
which can bias the observed relation towards steeper values. We corrected for
this bias and compared the measured relation to theoretical predictions
accounting for halo triaxiality, adiabatic contraction of the halo, presence of
a dominant BCG and, mostly, selection effects in the observed sample. The
normalisation, the slope and the scatter of the expected relation are strongly
sample-dependent. For the considered samples, the predicted slope is much
steeper than that of the underlying relation characterising dark-matter only
clusters. We found that the correction for statistical and selection biases in
observed relations mostly solve the tension with the CDM model.Comment: 13 pages, 3 figures; v2: 14 pages, minor changes, in press on MNRA
Predicting the number of giant arcs expected in the next generation wide-field surveys from space
In this paper we estimate the number of gravitational arcs detectable in a
wide-field survey such as that which will be operated by the Euclid space
mission, assuming a {\Lambda}CDM cosmology. We use the publicly available code
MOKA to obtain realistic deflection angle maps of mock gravitational lenses.
The maps are processed by a ray-tracing code to estimate the strong lensing
cross sections of each lens. Our procedure involves 1) the generation of a
light-cone which is populated with lenses drawn from a theoretical
mass-function; 2) the modeling of each single lens using a triaxial halo with a
NFW (Navarro-Frenk-White) density profile and theoretical concentration-mass
relation, including substructures, 3) the determination of the lensing cross
section as a function of redshift for each lens in the light-cone, 4) the
simulation of mock observations to characterize the redshift distribution of
sources that will be detectable in the Euclid images. We focus on the so-called
giant arcs, i.e. gravitational arcs characterized by large length-to-width
ratios (l/w > 5, 7.5 and 10). We quantify the arc detectability at different
significances above the level of the background. Performing 128 different
realizations of a 15,000 sq. degree survey, we find that the number of arcs
detectable at 1{\sigma} above the local background will be 8912,2914, and 1275
for l/w>5, 7.5 and 10, respectively. The expected arc numbers decrease to 2409,
790, and 346 for a detection limit at 3{\sigma} above the background level.
From our analysis, we find that most of the lenses which contribute to the
lensing optical depth are located at redshifts 0.4<zl<0.7 and that the 50% of
the arcs are images of sources at zs > 3. This is the first step towards the
full characterization of the population of strong lenses that will be observed
by Euclid. [abridged]Comment: replaced to match the accepted version by MNRAS, 12 pag, 10 fig -
more references adde
Characterizing dark interactions with the halo mass accretion history and structural properties
We study the halo mass accretion history (MAH) and its correlation with the
internal structural properties in coupled dark energy cosmologies (cDE). To
accurately predict all the non-linear effects caused by dark interactions, we
use the COupled Dark Energy Cosmological Simulations (CoDECS). We measure the
halo concentration at z=0 and the number of substructures above a mass
resolution threshold for each halo. Tracing the halo merging history trees back
in time, following the mass of the main halo, we develope a MAH model that
accurately reproduces the halo growth in term of M_{200} in the {\Lambda}CDM
Universe; we then compare the MAH in different cosmological scenarios. For cDE
models with a weak constant coupling, our MAH model can reproduce the
simulation results, within 10% of accuracy, by suitably rescaling the
normalization of the linear matter power spectrum at z=0, {\sigma}_8. However,
this is not the case for more complex scenarios, like the "bouncing" cDE model,
for which the numerical analysis shows a rapid growth of haloes at high
redshifts, that cannot be reproduced by simply rescaling the value of
{\sigma}_8. Moreover, at fixed value of {\sigma}_8, cold dark matter (CDM)
haloes in these cDE scenarios tend to be more concentrated and have a larger
amount of substructures with respect to {\Lambda}CDM predictions. Finally, we
present an accurate model that relates the halo concentration to the time at
which it assembles half or 4% of its mass. Combining this with our MAH model,
we show how halo concentrations change while varying only {\sigma}_8 in a
{\Lambda}CDM Universe, at fixed halo mass.Comment: 18 pages, 14 figures, accepted for publication in MNRA
Mass and Concentration estimates from Weak and Strong Gravitational Lensing: a Systematic Study
We study how well halo properties of galaxy clusters, like mass and
concentration, are recovered using lensing data. In order to generate a large
sample of systems at different redshifts we use the code MOKA. We measure halo
mass and concentration using weak lensing data alone (WL), fitting to an NFW
profile the reduced tangential shear profile, or by combining weak and strong
lensing data, by adding information about the size of the Einstein radius
(WL+SL). For different redshifts, we measure the mass and the concentration
biases and find that these are mainly caused by the random orientation of the
halo ellipsoid with respect to the line-of-sight. Since our simulations account
for the presence of a bright central galaxy, we perform mass and concentration
measurements using a generalized NFW profile which allows for a free inner
slope. This reduces both the mass and the concentration biases. We discuss how
the mass function and the concentration mass relation change when using WL and
WL+SL estimates. We investigate how selection effects impact the measured
concentration-mass relation showing that strong lens clusters may have a
concentration 20-30% higher than the average, at fixed mass, considering also
the particular case of strong lensing selected samples of relaxed clusters.
Finally, we notice that selecting a sample of relaxed galaxy clusters, as is
done in some cluster surveys, explain the concentration-mass relation biases.Comment: (1) DIFA-UniBO, (2) INAF-OABo, (3) INFN-BO, (4) JPL-Pasadena 18
pages, 19 figures - accepted for publication by MNRAS, two figures added for
comparison with SGAS-SDSS and LoCuSS cluster
Sussidiarietà e istruzione tecnico-professionale in Italia. Note metodologiche per la ricerca
Technical education and training is now interested by a reform process, trying to integrate the different paths that a student can follow to get a technical degree: the professional schools and training courses. Another challenge is that of integrating in the new system the lessons coming from best innovative practices in the field of the fight to early school living. For this reason the level of application of subsidiarity principle can help to explain differences in the job and social outcome for students. The paper analyses the methodological aspects to be afforded to design a research on the level and effects of subsidiarity in the technical educational system.Technical and professional education, training evaluation, placement evaluation, subsidiaity, educational system reform.
Weak Lensing Peaks in Simulated Light-Cones: Investigating the Coupling between Dark Matter and Dark Energy
In this paper, we study the statistical properties of weak lensing peaks in
light-cones generated from cosmological simulations. In order to assess the
prospects of such observable as a cosmological probe, we consider simulations
that include interacting Dark Energy (hereafter DE) models with coupling term
between DE and Dark Matter. Cosmological models that produce a larger
population of massive clusters have more numerous high signal-to-noise peaks;
among models with comparable numbers of clusters those with more concentrated
haloes produce more peaks. The most extreme model under investigation shows a
difference in peak counts of about with respect to the reference
CDM model. We find that peak statistics can be used to
distinguish a coupling DE model from a reference one with the same power
spectrum normalisation. The differences in the expansion history and the growth
rate of structure formation are reflected in their halo counts, non-linear
scale features and, through them, in the properties of the lensing peaks. For a
source redshift distribution consistent with the expectations of future
space-based wide field surveys, we find that typically seventy percent of the
cluster population contributes to weak-lensing peaks with signal-to-noise
ratios larger than two, and that the fraction of clusters in peaks approaches
one-hundred percent for haloes with redshift z0.5. Our analysis
demonstrates that peak statistics are an important tool for disentangling DE
models by accurately tracing the structure formation processes as a function of
the cosmic time.Comment: accepted in MNRAS, figures improved and text update
On the Physical Reasons for the Extension of Symmetry Groups in Molecular Spectroscopy
Several situations of general interest, in which the symmetry groups usually applied to spectroscopy problems need to be extended, are reviewed. It is emphasized that any symmetry group of geometrical operations to be used in Molecular Spectroscopy should be extended for completeness by considering the time reversal operator, as far as the Hamiltonian is invariant with respect to the inversion of the direction of motion. This can explain the degeneracy of pairs of vibrational and rotational states spanning the so-called separably degenerate irreducible representations, in symmetric tops of low symmetry, and Kramers degeneracy in odd electron molecules in the absence of magnetic fields. An extension with account of time reversal is also useful to determine relative phase conventions on vibration-rotation wavefunctions, which render all vibration-rotation matrix elements real. An extension of a molecular symmetry group may be required for molecules which can attain different geometries by large amplitude periodical motions, if such motions are hindered and are not completely free. Special cases involving the internal rotation are discussed in detail. It is observed that the symmetry classification of vibrational modes involving displacements normal to the internal rotation axis is not univocal, but can be done in several ways, which actually correspond to different conventions on the separation of vibration and internal rotation in the adopted basis functions. The symmetry species of the separate vibrational and torsional factors of these functions depend on the adopted convention
Role of the polygalacturonate network on the iron (III) reduction by caffeic acid
This communication reports the role of polygalacturonate network on the Fe(III) reduction by caffeic acid. The effect of phosphate ions on the redox reaction is also considered
Cosmology through arc statistics I: sensitivity to and
The next generation of large sky photometric surveys will finally be able to
use arc statistics as a cosmological probe. Here we present the first of a
series of papers on this topic. In particular, we study how arc counts are
sensitive to the variation of two cosmological parameters: the (total) matter
density parameter, , and the normalisation of the primordial power
spectrum, expressed in terms of . Both these parameters influence the
abundances of collapsed structures and their internal structure. We compute the
expected number of gravitational arcs with various length-to-width ratios in
mock light cones, by varying these cosmological parameters in the ranges
and . We find that the arc
counts dependence on and is similar, but not identical,
to that of the halo counts. We investigate how the precision of the constraints
on the cosmological parameters based on arc counts depends on the survey area.
We find that the constraining power of arc statistics degrades critically only
for surveys covering an area smaller than of the whole sky. Finally, we
consider the case in which the search for arcs is done only in frames where
galaxy clusters have been previously identified. Adopting the selection
function for galaxy clusters expected to be detected from photometric data in
future wide surveys, we find that less than of the arcs will be missed,
with only a small degradation of the corresponding cosmological constraints.Comment: 12 pages, 12 figures, accepted by MNRA
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