450 research outputs found
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
Electrical resistivity tomography for studying liquefaction induced by the May 2012 Emilia-Romagna earthquake (Mw = 6.1, northern Italy)
Abstract. This work shows the result of an electrical resistivity tomography (ERT) survey carried out for imaging and characterizing the shallow subsurface affected by the coseismic effects of the Mw = 6.1 Emilia-Romagna (northern Italy) earthquake that occurred on 20 May 2012. The most characteristic coseismic effects were ground failure, lateral spreading and liquefaction that occurred extensively along the paleo-Reno River in the urban areas of San Carlo and Mirabello (southwestern portion of Ferrara Province). In total, six electrical resistivity tomographies were performed and calibrated with surface geological surveys, exploratory boreholes and aerial photo interpretations. This was one of first applications of the electrical resistivity tomography method in investigating coseismic liquefaction
Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster Survey
We study the characteristics of the galaxy cluster samples expected from the
European Space Agency's Euclid satellite and forecast constraints on
cosmological parameters describing a variety of cosmological models. The method
used in this paper, based on the Fisher Matrix approach, is the same one used
to provide the constraints presented in the Euclid Red Book (Laureijs et
al.2011). We describe the analytical approach to compute the selection function
of the photometric and spectroscopic cluster surveys. Based on the photometric
selection function, we forecast the constraints on a number of cosmological
parameter sets corresponding to different extensions of the standard LambdaCDM
model. The dynamical evolution of dark energy will be constrained to Delta
w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a
(w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance
matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a
FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL,
will be constrained to \Delta f_NL ~ 6.6 for the local shape scenario, from
Euclid clusters alone. Using only Euclid clusters, the growth factor parameter
\gamma, which signals deviations from GR, will be constrained to Delta
\gamma=0.02, and the neutrino density parameter to Delta Omega_\nu=0.0013 (or
Delta \sum m_\nu=0.01). We emphasise that knowledge of the observable--mass
scaling relation will be crucial to constrain cosmological parameters from a
cluster catalogue. The Euclid mission will have a clear advantage in this
respect, thanks to its imaging and spectroscopic capabilities that will enable
internal mass calibration from weak lensing and the dynamics of cluster
galaxies. This information will be further complemented by wide-area
multi-wavelength external cluster surveys that will already be available when
Euclid flies. [Abridged]Comment: submitted to MNRA
The Population of Dark Matter Subhaloes: Mass Functions and Average Mass Loss Rates
Using a cosmological N-Body simulation and a sample of re-simulated
cluster-like haloes, we study the mass loss rates of dark matter subhaloes, and
interpret the mass function of subhaloes at redshift zero in terms of the
evolution of the mass function of systems accreted by the main halo progenitor.
When expressed in terms of the ratio between the mass of the subhalo at the
time of accretion and the present day host mass the unevolved subhalo mass
function is found to be universal. However, the subhalo mass function at
redshift zero clearly depends on , in that more massive host haloes host
more subhaloes. To relate the unevolved and evolved subhalo mass functions, we
measure the subhalo mass loss rate as a function of host mass and redshift. We
find that the average, specific mass loss rate of dark matter subhaloes depends
mainly on redshift. These results suggest a pleasingly simple picture for the
evolution and mass dependence of the evolved subhalo mass function. Less
massive host haloes accrete their subhaloes earlier, which are thus subjected
to mass loss for a longer time. In addition, their subhaloes are typically
accreted by denser hosts, which causes an additional boost of the mass loss
rate. To test the self-consistency of this picture, we use a merger trees
constructed using the extended Press-Schechter formalism, and evolve the
subhalo populations using the average mass loss rates obtained from our
simulations, finding the subhalo mass functions to be in good agreement with
the simulations. [abridged]Comment: 12 pages, 12 figures; submitted to MNRA
A PCA-based automated finder for galaxy-scale strong lenses
We present an algorithm using Principal Component Analysis (PCA) to subtract
galaxies from imaging data, and also two algorithms to find strong,
galaxy-scale gravitational lenses in the resulting residual image. The combined
method is optimized to find full or partial Einstein rings. Starting from a
pre-selection of potential massive galaxies, we first perform a PCA to build a
set of basis vectors. The galaxy images are reconstructed using the PCA basis
and subtracted from the data. We then filter the residual image with two
different methods. The first uses a curvelet (curved wavelets) filter of the
residual images to enhance any curved/ring feature. The resulting image is
transformed in polar coordinates, centered on the lens galaxy center. In these
coordinates, a ring is turned into a line, allowing us to detect very faint
rings by taking advantage of the integrated signal-to-noise in the ring (a line
in polar coordinates). The second way of analysing the PCA-subtracted images
identifies structures in the residual images and assesses whether they are
lensed images according to their orientation, multiplicity and elongation. We
apply the two methods to a sample of simulated Einstein rings, as they would be
observed with the ESA Euclid satellite in the VIS band. The polar coordinates
transform allows us to reach a completeness of 90% and a purity of 86%, as soon
as the signal-to-noise integrated in the ring is higher than 30, and almost
independent of the size of the Einstein ring. Finally, we show with real data
that our PCA-based galaxy subtraction scheme performs better than traditional
subtraction based on model fitting to the data. Our algorithm can be developed
and improved further using machine learning and dictionary learning methods,
which would extend the capabilities of the method to more complex and diverse
galaxy shapes
On the road to per cent accuracy - V. The non-linear power spectrum beyond ÎCDM with massive neutrinos and baryonic feedback
In the context of forthcoming galaxy surveys, to ensure unbiased constraints on cosmology and gravity when using non-linear structure information, per cent-level accuracy is required when modelling the power spectrum. This calls for frameworks that can accurately capture the relevant physical effects, while allowing for deviations from Lambda cold dark matter (ÎCDM). Massive neutrino and baryonic physics are two of the most relevant such effects. We present an integration of the halo model reaction frameworks for massive neutrinos and beyond ÎCDM cosmologies. The integrated halo model reaction, combined with a pseudo-power spectrum modelled by HMCode2020 is then compared against N-body simulations that include both massive neutrinos and an f(R) modification to gravity. We find that the framework is 4 per cent accurate down to at least â 3 h Mpc-1 for a modification to gravity of |fR0| †10-5 and for the total neutrino mass MÎœ ÎŁmÎœ †0.15 eV. We also find that the framework is 4 per cent consistent with EuclidEmulator2 as well as the Bacco emulator for most of the considered ÎœwCDM cosmologies down to at least k â 3 h Mpc-1. Finally, we compare against hydrodynamical simulations employing HMCode2020's baryonic feedback modelling on top of the halo model reaction. For ÎœÎCDM cosmologies, we find 2 per cent accuracy for MÎœ †0.48 eV down to at least k â 5h Mpc-1. Similar accuracy is found when comparing to ÎœwCDM hydrodynamical simulations with MÎœ = 0.06 eV. This offers the first non-linear, theoretically general means of accurately including massive neutrinos for beyond-ÎCDM cosmologies, and further suggests that baryonic, massive neutrino, and dark energy physics can be reliably modelled independently
Enhanced cluster lensing models with measured galaxy kinematics
We present an improved determination of the total mass distribution of three massive clusters from the Cluster Lensing and Supernova Survey with Hubble and Hubble Frontier Fields, MACS J1206.2-0847 (z = 0.44), MACS J0416.1-2403 (z = 0.40), Abell S1063 (z = 0.35). We specifically reconstructed the sub-halo mass component with robust stellar kinematics information of cluster galaxies, in combination with precise strong lensing models based on large samples of spectroscopically identified multiple images. We used integral-field spectroscopy in the cluster cores, from the Multi Unit Spectroscopic Explorer on the Very Large Telescope, to measure the stellar velocity dispersion, Ï, of 40-60 member galaxies per cluster, covering four to five magnitudes to mF160W â 21.5. We verified the robustness and quantified the accuracy of the velocity dispersion measurements with extensive spectral simulations. With these data, we determined the normalization and slope of the galaxy L-Ï Faber-Jackson relation in each cluster and used these parameters as a prior for the scaling relations of the sub-halo population in the mass distribution modeling. When compared to our previous lens models, the inclusion of member galaxies' kinematics provides a similar precision in reproducing the positions of the multiple images. However, the inherent degeneracy between the central effective velocity dispersion, Ï0, and truncation radius, rcut, of sub-halos is strongly reduced, thus significantly alleviating possible systematics in the measurements of sub-halo masses. The three independent determinations of the Ï0 - rcut scaling relation in each cluster are found to be fully consistent, enabling a statistical determination of sub-halo sizes as a function of Ï0, or halo masses. Finally, we derived the galaxy central velocity dispersion functions of the three clusters projected within 16% of their virial radius, finding that they are well in agreement with each other. We argue that such a methodology, when applied to high-quality kinematics and strong lensing data, allows the sub-halo mass functions to be determined and compared with those obtained from cosmological simulations
Bailing Out the Milky Way: Variation in the Properties of Massive Dwarfs Among Galaxy-Sized Systems
Recent kinematical constraints on the internal densities of the Milky Way's
dwarf satellites have revealed a discrepancy with the subhalo populations of
simulated Galaxy-scale halos in the standard CDM model of hierarchical
structure formation. This has been dubbed the "too big to fail" problem, with
reference to the improbability of large and invisible companions existing in
the Galactic environment. In this paper, we argue that both the Milky Way
observations and simulated subhalos are consistent with the predictions of the
standard model for structure formation. Specifically, we show that there is
significant variation in the properties of subhalos among distinct host halos
of fixed mass and suggest that this can reasonably account for the deficit of
dense satellites in the Milky Way. We exploit well-tested analytic techniques
to predict the properties in a large sample of distinct host halos with a
variety of masses spanning the range expected of the Galactic halo. The
analytic model produces subhalo populations consistent with both Via Lactea II
and Aquarius, and our results suggest that natural variation in subhalo
properties suffices to explain the discrepancy between Milky Way satellite
kinematics and these numerical simulations. At least ~10% of Milky Way-sized
halos host subhalo populations for which there is no "too big to fail" problem,
even when the host halo mass is as large as M_host = 10^12.2 h^-1 M_sun.
Follow-up studies consisting of high-resolution simulations of a large number
of Milky Way-sized hosts are necessary to confirm our predictions. In the
absence of such efforts, the "too big to fail" problem does not appear to be a
significant challenge to the standard model of hierarchical formation.
[abridged]Comment: 12 pages, 3 figures; accepted by JCAP. Replaced with published
versio
Mass assembly of galaxies: Smooth accretion versus mergers
Galaxies accrete their mass by means of both smooth accretion from the cosmic
web, and the mergers of smaller entities. We wish to quantify the respective
role of these two modes of accretion, which could determine the morphological
types of galaxies observed today. Multi-zoom cosmological simulations are used
to estimate as a function of time the evolution of mass in bound systems, for
dark matter as well as baryons. The baryonic contents of dark matter haloes are
studied. Merger histories are followed as a function of external density, and
the different ways in which mass is assembled in galaxies and the stellar
component accumulated are quantified. We find that most galaxies assemble their
mass through smooth accretion, and only the most massive galaxies also grow
significantly through mergers. The mean fraction of mass assembled by accretion
is 77 %, and by mergers 23 %. We present typical accretion histories of
hundreds of galaxies: masses of the most massive galaxies increase
monotonically in time, mainly through accretion, many intermediate-mass objects
also experience mass-loss events such as tidal stripping and evaporation.
However, our simulations suffer from the overcooling of massive galaxies caused
by the neglect of active galaxy nuclei (AGN) feedback. The time by which half
of the galay mass has assembled, both in dark matter and baryons, is a
decreasing function of mass, which is compatible with the observations of a
so-called downsizing. At every epoch in the universe, there are low-mass
galaxies actively forming stars, while more massive galaxies form their stars
over a shorter period of time within half the age of the universe.Comment: A&A Accepted, 19 pages, 17 figure
AMICO galaxy clusters in KiDS-DR3: Cosmological constraints from angular power spectrum and correlation function
We study the tomographic clustering properties of the photometric cluster
catalogue derived from the Third Data Release of the Kilo Degree Survey,
focusing on the angular correlation function and its spherical harmonic
counterpart, the angular power spectrum. We measure the angular correlation
function and power spectrum from a sample of 5162 clusters, with an intrinsic
richness , in the photometric redshift range , comparing our measurements with theoretical models, in the framework of
the -Cold Dark Matter cosmology. We perform a Monte Carlo Markov Chain
analysis to constrain the cosmological parameters ,
and the structure growth parameter . We adopt Gaussian priors on the parameters of
the mass-richness relation, based on the posterior distributions derived from a
previous joint analysis of cluster counts and weak lensing mass measurements
carried out with the same catalogue. From the angular correlation function, we
obtain ,
and , in agreement,
within , with 3D clustering result based on the same cluster sample
and with existing complementary studies on other datasets. For the angular
power spectrum, we derive statistically consistent results, in particular
and ,
while the constraint on alone is weaker with respect to the one
provided by the angular correlation function, .
Our results show that the 2D clustering from photometric cluster surveys can
provide competitive cosmological constraints with respect to the full 3D
clustering statistics, and can be successfully applied to ongoing and
forthcoming spectro/photometric surveys.Comment: 14 pages, 9 figures. Submitted to Astronomy & Astrophysics (A&A
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