224 research outputs found
The halo 3-point correlation function: a methodological analysis
Upcoming galaxy surveys will provide us with an unprecedented view of the Large -Scale Structure of the Universe and the realistic chance to extract valuable astrophysical and cosmological information from higher-order clustering statistics. This perspective poses new challenges, requiring both accurate and efficient estimators and a renewed assessment of possible systematic errors in the theoretical models and likelihood assumptions. This work investigates these issues in relation to the analysis of the 3-point correlation function (3PCF) in configuration space. We measure the 3PCF of 300 halo catalogs from the MINERVA simulations covering a total volume of 1000h-3Gpc3. Each 3PCF measurement includes all possible triangular configurations with sides between 20 and 130h-1 Mpc. In the first place, we test different estimates of the covariance matrix, a crucial aspect of the analysis. We compare the covariance computed numerically from the limited but accurate benchmark simulations set to the one obtained from 10000 approximate halo catalogs generated with the PINOCCHIO code. We demonstrate that the two numerically-estimated covariance matrices largely match, confirming the validity of approximate methods based on Lagrangian Perturbation Theory for generating mocks suitable for covariance estimation. We also compare the numerical covariance with a theoretical prediction in the Gaussian approximation. We find a good match between the two for separations above 40h-1 Mpc. We test the 3PCF tree-level model in Perturbation Theory. The model is adopted in a likelihood analysis aimed at the determination of bias parameters. We find that, for our sample of halos at redshift z = 1, the tree-level model performs well for separations r > 40h-1 Mpc. Results obtained with this scale cut are robust against different choices of covariance matrix. We compare to the analogous analysis of the halo bispectrum already presented in a previous publication, finding a remarkable agreement between the two statistics. We notice that such comparison relies, to the best of our knowledge for the first time, on a robust and consistent covariance estimate and on the inclusion of essentially all measurable configurations in Fourier as in configuration space. We then test different assumptions to build the model defining a robust combination of hypotheses that lead to unbiased parameter estimates. Our results confirm the importance of 3PCF, supplying a solid recipe for its inclusion in likelihood analyses. Moreover, it opens the path for further improvements, especially in modelling, to extract information from non-linear regimes
A forecasting model to estimate the drop in blood supplies during the SARS-CoV-2 pandemic in Italy
Objectives: To estimate the number of actually Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) infected blood donors applying a statistical forecasting model. Background: Following the outbreak of the SARS-CoV-2 epidemic, a drop in blood donation has been observed. It is crucial to determine the actual number of potential SARS-CoV-2-positive donors to define the measures and ensure adequate blood supply. Methods: The cumulative incidence of SARS-CoV-2 positivity, calculated on the general population, was applied to the donor population by estimating the number of positive subjects. The calculation model was validated by the linear interpolation method. The number of blood units actually discarded based on post-donation information was also taken into account. Results: Three months after the outbreak, 5322 donors were estimated to be positive for SARS-CoV-2 and were therefore potentially excluded from donation. A total of units of blood components were discarded following post donation information. The estimated number of donors deceased (180) and the number of clinically recovered individuals in the same period was also considered. Conclusion: This forecasting model can be used to obtain information on blood donors' involvement during future SARS-CoV-2 outbreaks, especially in case of changes concerning epidemiology, incidence by age bracket and geographical distribution and also for new outbreaks of emerging viruses
AMICO galaxy clusters in KiDS-DR3: cosmological constraints from counts and stacked weak-lensing
We present a cosmological analysis of abundances and stacked weak-lensing
profiles of galaxy clusters, exploiting the AMICO KiDS-DR3 catalogue. The
sample consists of 3652 galaxy clusters with intrinsic richness
, over an effective area of 377 deg, in the redshift range
. We quantified the purity and completeness of the sample
through simulations. The statistical analysis has been performed by
simultaneously modelling the comoving number density of galaxy clusters and the
scaling relation between the intrinsic richnesses and the cluster masses,
assessed through a stacked weak-lensing profile modelling. The fluctuations of
the matter background density, caused by super-survey modes, have been taken
into account in the likelihood. Assuming a flat CDM model, we
constrained , , , and the parameters of the mass-richness scaling relation. We
obtained ,
, . The constraint on
is consistent within 1 with the results from WMAP and Planck.
Furthermore, we got constraints on the cluster mass scaling relation in
agreement with those obtained from a previous weak-lensing only analysis.Comment: 12 pages, 7 figures, 2 tables. Accepted by A&
D-dimer testing, with gender-specific cutoff levels, is of value to assess the individual risk of venous thromboembolic recurrence in non-elderly patients of both genders: a post hoc analysis of the DULCIS study
Male patients, especially the young, are at a higher risk of recurrent venous thromboembolism (RVTE) than females. Recent scientific reports show the use of D-dimer does not help predict RVTE risk in males. In the present report, we reviewed the data obtained in the DULCIS study (main report published in Blood 2014), focusing on D-dimer results recorded in non-elderly patients of both genders included in the study, and their relationship with RVTE events occurring during follow-up. Using specifically designed cutoff values for positive/negative interpretation, serial D-dimer measurements (performed during warfarin treatment and up to 3 months after discontinuation of anticoagulation) in 475 patients (males 57.3%) aged 64 65 years were obtained. D-dimer resulted positive in 46.3% and 30.5% of males and females, respectively (p = 0.001). Following management procedure, anticoagulation was stopped in 53.7% of males and 69.5% of females, who had persistently negative D-dimer results. The rate of subsequent recurrent events was 1.7% (95% CI 0.5\u20134.5%) and 0.4% (95% CI 0\u20132.5%) patient-years in males and females, respectively, with upper limits of confidence intervals always below the level of risk considered acceptable by international scientific societies for stopping anticoagulation (< 5%). In conclusion, using sensitive quantitative assays with specifically designed cutoff values and serial measurements during and after discontinuation of anticoagulation, D-dimer testing is useful to predict the risk of RVTE and is of help in deciding the duration of anticoagulation in both male and female adult patients aged up to 65 years
Red blood cell alloimmunisation in transfusion-dependent thalassaemia: a systematic review.
BACKGROUND: Chronic red blood cell transfusion is the first-line treatment for severe forms of thalassaemia. This therapy is, however, hampered by a number of adverse effects, including red blood cell alloimmunisation. The aim of this systematic review was to collect the current literature data on erythrocyte alloimmunisation. MATERIALS AND METHODS: We performed a systematic search of the literature which identified 41 cohort studies involving 9,256 patients. RESULTS: The prevalence of erythrocyte alloimmunisation was 11.4% (95% CI: 9.3-13.9%) with a higher rate of alloimmunisation against antigens of the Rh (52.4%) and Kell (25.6%) systems. Overall, alloantibodies against antigens belonging to the Rh and Kell systems accounted for 78% of the cases. A higher prevalence of red blood cell alloimmunisation was found in patients with thalassaemia intermedia compared to that among patients with thalassaemia major (15.5 vs 12.8%). DISCUSSION: Matching transfusion-dependent thalassaemia patients and red blood cell units for Rh and Kell antigens should be able to reduce the risk of red blood cell alloimmunisation by about 80%
Euclid: Cosmological forecasts from the void size function
The Euclid mission with its spectroscopic galaxy survey covering a sky area over in the redshift range will provide a sample of tens of thousands of cosmic voids. This paper explores for the first time the constraining power of the void size function on the properties of dark energy (DE) from a survey mock catalogue, the official Euclid Flagship simulation. We identify voids in the Flagship light-cone, which closely matches the features of the upcoming Euclid spectroscopic data set. We model the void size function considering a state-of-the art methodology: we rely on the volume conserving (Vdn) model, a modification of the popular Sheth & van de Weygaert model for void number counts, extended by means of a linear function of the large-scale galaxy bias. We find an excellent agreement between model predictions and measured mock void number counts. We compute updated forecasts for the Euclid mission on DE from the void size function and provide reliable void number estimates to serve as a basis for further forecasts of cosmological applications using voids. We analyse two different cosmological models for DE: the first described by a constant DE equation of state parameter, , and the second by a dynamic equation of state with coefficients and . We forecast errors on lower than the , and we estimate an expected figure of merit (FoM) for the dynamical DE scenario when considering only the neutrino mass as additional free parameter of the model. The analysis is based on conservative assumptions to ensure full robustness, and is a pathfinder for future enhancements of the technique. Our results showcase the impressive constraining power of the void size function from the Euclid spectroscopic sample, both as a stand-alone probe, and to be combined with other Euclid cosmological probes...
The XXL survey: first results and future
The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions
Euclid preparation. XXIV. Calibration of the halo mass function in CDM cosmologies
Euclid's photometric galaxy cluster survey has the potential to be a very
competitive cosmological probe. The main cosmological probe with observations
of clusters is their number count, within which the halo mass function (HMF) is
a key theoretical quantity. We present a new calibration of the analytic HMF,
at the level of accuracy and precision required for the uncertainty in this
quantity to be subdominant with respect to other sources of uncertainty in
recovering cosmological parameters from Euclid cluster counts. Our model is
calibrated against a suite of N-body simulations using a Bayesian approach
taking into account systematic errors arising from numerical effects in the
simulation. First, we test the convergence of HMF predictions from different
N-body codes, by using initial conditions generated with different orders of
Lagrangian Perturbation theory, and adopting different simulation box sizes and
mass resolution. Then, we quantify the effect of using different halo-finder
algorithms, and how the resulting differences propagate to the cosmological
constraints. In order to trace the violation of universality in the HMF, we
also analyse simulations based on initial conditions characterised by
scale-free power spectra with different spectral indexes, assuming both
Einstein--de Sitter and standard CDM expansion histories. Based on
these results, we construct a fitting function for the HMF that we demonstrate
to be sub-percent accurate in reproducing results from 9 different variants of
the CDM model including massive neutrinos cosmologies. The calibration
systematic uncertainty is largely sub-dominant with respect to the expected
precision of future mass-observation relations; with the only notable exception
of the effect due to the halo finder, that could lead to biased cosmological
inference.Comment: 24 pages, 21 figures, 5 tables, 3 appendixes
Euclid preparation. TBD. The effect of linear redshift-space distortions in photometric galaxy clustering and its cross-correlation with cosmic shear
Cosmological surveys planned for the current decade will provide us with
unparalleled observations of the distribution of galaxies on cosmic scales, by
means of which we can probe the underlying large-scale structure (LSS) of the
Universe. This will allow us to test the concordance cosmological model and its
extensions. However, precision pushes us to high levels of accuracy in the
theoretical modelling of the LSS observables, in order not to introduce biases
in the estimation of cosmological parameters. In particular, effects such as
redshift-space distortions (RSD) can become relevant in the computation of
harmonic-space power spectra even for the clustering of the photometrically
selected galaxies, as it has been previously shown in literature studies. In
this work, we investigate the contribution of linear RSD, as formulated in the
Limber approximation by arXiv:1902.07226, in forecast cosmological analyses
with the photometric galaxy sample of the Euclid survey, in order to assess
their impact and quantify the bias on the measurement of cosmological
parameters that neglecting such an effect would cause. We perform this task by
producing mock power spectra for photometric galaxy clustering and weak
lensing, as expected to be obtained from the Euclid survey. We then use a
Markov chain Monte Carlo approach to obtain the posterior distributions of
cosmological parameters from such simulated observations. We find that
neglecting the linear RSD leads to significant biases both when using galaxy
correlations alone and when these are combined with cosmic shear, in the
so-called 32pt approach. Such biases can be as large as
-equivalent when assuming an underlying CDM cosmology. When
extending the cosmological model to include the equation-of-state parameters of
dark energy, we find that the extension parameters can be shifted by more than
.Comment: 15 pages, 5 figures. To be submitted in A&
Euclid preparation. XXXI. The effect of the variations in photometric passbands on photometric-redshift accuracy
The technique of photometric redshifts has become essential for the
exploitation of multi-band extragalactic surveys. While the requirements on
photo-zs for the study of galaxy evolution mostly pertain to the precision and
to the fraction of outliers, the most stringent requirement in their use in
cosmology is on the accuracy, with a level of bias at the sub-percent level for
the Euclid cosmology mission. A separate, and challenging, calibration process
is needed to control the bias at this level of accuracy. The bias in photo-zs
has several distinct origins that may not always be easily overcome. We
identify here one source of bias linked to the spatial or time variability of
the passbands used to determine the photometric colours of galaxies. We first
quantified the effect as observed on several well-known photometric cameras,
and found in particular that, due to the properties of optical filters, the
redshifts of off-axis sources are usually overestimated. We show using simple
simulations that the detailed and complex changes in the shape can be mostly
ignored and that it is sufficient to know the mean wavelength of the passbands
of each photometric observation to correct almost exactly for this bias; the
key point is that this mean wavelength is independent of the spectral energy
distribution of the source}. We use this property to propose a correction that
can be computationally efficiently implemented in some photo-z algorithms, in
particular template-fitting. We verified that our algorithm, implemented in the
new photo-z code Phosphoros, can effectively reduce the bias in photo-zs on
real data using the CFHTLS T007 survey, with an average measured bias Delta z
over the redshift range 0.4<z<0.7 decreasing by about 0.02, specifically from
Delta z~0.04 to Delta z~0.02 around z=0.5. Our algorithm is also able to
produce corrected photometry for other applications.Comment: 19 pages, 13 figures; Accepted for publication in A&
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