80 research outputs found
Delivering safe and effective hemodialysis in patients with suspected or confirmed COVID-19 infection : a single-center perspective from Italy
Large scale distribution of total mass versus luminous matter from Baryon Acoustic Oscillations: First search in the SDSS-III BOSS Data Release 10
Baryon Acoustic Oscillations (BAOs) in the early Universe are predicted to
leave an as yet undetected signature on the relative clustering of total mass
versus luminous matter. A detection of this effect would provide an important
confirmation of the standard cosmological paradigm and constrain alternatives
to dark matter as well as non-standard fluctuations such as Compensated
Isocurvature Perturbations (CIPs). We conduct the first observational search
for this effect, by comparing the number-weighted and luminosity-weighted
correlation functions, using the SDSS-III BOSS Data Release 10 CMASS sample.
When including CIPs in our model, we formally obtain evidence at of
the relative clustering signature and a limit that matches the existing upper
limits on the amplitude of CIPs. However, various tests suggest that these
results are not yet robust, perhaps due to systematic biases in the data. The
method developed in this Letter, used with more accurate future data such as
that from DESI, is likely to confirm or disprove our preliminary evidence.Comment: 6 pages, 2 figures, accepted for publication in PR
Comparison of spatial distributions of Intracluster light and Dark Matter
In a galaxy cluster, the relative spatial distributions of dark matter,
member galaxies, gas, and intracluster light (ICL) may connote their mutual
interactions over the cluster evolution. However, it is a challenging problem
to provide a quantitative measure for the shape matching between two
multi-dimensional scalar distributions. We present a novel methodology, named
the {\em Weighted Overlap Coefficient (WOC)}, to quantify the similarity of
2-dimensional spatial distributions. We compare the WOC with a standard method
known as the Modified Hausdorff Distance (MHD). We find that our method is
robust, and performs well even with the existence of multiple sub-structures.
We apply our methodology to search for a visible component whose spatial
distribution resembled with that of dark matter. If such a component could be
found to trace the dark matter distribution with high fidelity for more relaxed
galaxy clusters, then the similarity of the distributions could also be used as
a dynamical stage estimator of the cluster. We apply the method to six galaxy
clusters at different dynamical stages simulated within the GRT simulation,
which is an N-body simulation using the galaxy replacement technique. Among the
various components (stellar particles, galaxies, ICL), the ICL+ brightest
cluster galaxy (BCG) component most faithfully trace the dark matter
distribution. Among the sample galaxy clusters, the relaxed clusters show
stronger similarity in the spatial distribution of the dark matter and ICL+BCG
than the dynamically young clusters. While the MHD results show weaker trend
with the dynamical stages.Comment: 17 pages, 8 figures, accepted in ApJ
A new Low Gain Avalanche Diode concept: the double-LGAD
This paper describes the new concept of the double-LGAD. The goal is to
increase the charge at the input of the electronics, keeping a time resolution
equal or better than a standard (single) LGAD; this has been realized by adding
the charges of two coupled LGADs while still using a single front-end
electronics. The study here reported has been done starting from single LGAD
with a thickness of 25 \textmu{m}, 35 \textmu{m} and 50 \textmu{m}.Comment: arXiv admin note: text overlap with arXiv:2208.0571
Statistical Determination of Bulk Flow Motions
We present here a new parameterization for the bulk motions of galaxies and
clusters (in the linear regime) that can be measured statistically from the
shape and amplitude of the two-dimensional two-point correlation function. We
further propose the one-dimensional velocity dispersion (v_p) of the bulk flow
as a complementary measure of redshift-space distortions, which is
model-independent and not dependent on the normalisation method. As a
demonstration, we have applied our new methodology to the C4 cluster catalogue
constructed from Data Release Three (DR3) of the Sloan Digital Sky Survey. We
find v_p=270^{+433}km/s (also consistent with v_p=0) for this cluster sample
(at z=0.1), which is in agreement with that predicted for a WMAP5-normalised
LCDM model (i.e., v_p(LCDM=203km/s). This measurement does not lend support to
recent claims of excessive bulk motions (\simeq1000 km/s) which appear in
conflict with LCDM, although our large statistical error cannot rule them out.
From the measured coherent evolution of v_p, we develop a technique to
re-construct the perturbed potential, as well as estimating the unbiased matter
density fluctuations and scale--independent bias.Comment: 8 pages, 5 figure
Measurements of the Cherenkov effect in direct detection of charged particles with SiPMs
In this paper, different Silicon PhotoMultiplier (SiPM) sensors have been
tested with charged particles to characterize the Cherenkov light produced in
the sensor protection layer. A careful position scan of the SiPM response has
been performed with different prototypes, confirming the large number of firing
cells and proving almost full efficiency, with the SiPM filling factor
essentially negligible. This study also allowed us to study the time resolution
of such devices as a function of the number of firing cells, reaching values
below 20 ps. These measurements provide significant insight into the
capabilities of SiPM sensors in direct detection of charged particles and their
potential for several applications
Star/galaxy separation at faint magnitudes: application to a simulated Dark Energy Survey
We address the problem of separating stars from galaxies in future large photometric surveys. We focus our analysis on simulations of the Dark Energy Survey (DES). In the first part of the paper, we derive the science requirements on star/galaxy separation, for measurement of the cosmological parameters with the gravitational weak lensing and large-scale structure probes. These requirements are dictated by the need to control both the statistical and systematic errors on the cosmological parameters, and by point spread function calibration. We formulate the requirements in terms of the completeness and purity provided by a given star/galaxy classifier. In order to achieve these requirements at faint magnitudes, we propose a new method for star/galaxy separation in the second part of the paper. We first use principal component analysis to outline the correlations between the objects parameters and extract from it the most relevant information. We then use the reduced set of parameters as input to an Artificial Neural Network. This multiparameter approach improves upon purely morphometric classifiers (such as the classifier implemented in SExtractor), especially at faint magnitudes: it increases the purity by up to 20 per cent for stars and by up to 12 per cent for galaxies, at i-magnitude fainter than 2
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey : baryon acoustic oscillations in the Data Releases 10 and 11 Galaxy samples
We present a one per cent measurement of the cosmic distance scale from the detections of the baryon acoustic oscillations (BAO) in the clustering of galaxies from the Baryon Oscillation Spectroscopic Survey, which is part of the Sloan Digital Sky Survey III. Our results come from the Data Release 11 (DR11) sample, containing nearly one million galaxies and covering approximately 8500 square degrees and the redshift range 0.2 < z < 0.7. We also compare these results with those from the publicly released DR9 and DR10 samples. Assuming a concordance Λ cold dark matter (ΛCDM) cosmological model, the DR11 sample covers a volume of 13 Gpc3 and is the largest region of the Universe ever surveyed at this density. We measure the correlation function and power spectrum, including density-field reconstruction of the BAO feature. The acoustic features are detected at a significance of over 7σ in both the correlation function and power spectrum. Fitting for the position of the acoustic features measures the distance relative to the sound horizon at the drag epoch, rd, which has a value of rd,fid = 149.28 Mpc in our fiducial cosmology. We find DV = (1264 ± 25 Mpc)(rd/rd,fid) at z = 0.32 and DV = (2056 ± 20 Mpc)(rd/rd,fid) at z = 0.57. At 1.0 per cent, this latter measure is the most precise distance constraint ever obtained from a galaxy survey. Separating the clustering along and transverse to the line of sight yields measurements at z = 0.57 of DA = (1421 ± 20 Mpc)(rd/rd,fid) and H = (96.8 ± 3.4 km s−1 Mpc−1)(rd,fid/rd). Our measurements of the distance scale are in good agreement with previous BAO measurements and with the predictions from cosmic microwave background data for a spatially flat CDM model with a cosmological constant.Publisher PDFPeer reviewe
Spatial Distribution of Intracluster Light versus Dark Matter in Horizon Run 5
One intriguing approach for studying the dynamical evolution of galaxy clusters is to compare the spatial distributions among various components such as dark matter, member galaxies, gas, and intracluster light (ICL). Utilizing the recently introduced weighted overlap coefficient (WOC), we analyze the spatial distributions of components within 174 galaxy clusters (M tot > 5 × 1013 M ⊙, z = 0.625) at varying dynamical states in the cosmological hydrodynamical simulation Horizon Run 5. We observe that the distributions of gas and the combination of ICL with the brightest cluster galaxy (BCG) closely resembles the dark matter distribution, particularly in more relaxed clusters, characterized by the half-mass epoch. The similarity in spatial distribution between dark matter and BCG+ICL mimics the changes in the dynamical state of clusters during a major merger. Notably, at redshifts >1, BCG+ICL traced dark matter more accurately than the gas. Additionally, we examined the one-dimensional radial profiles of each component, which show that the BCG+ICL is a sensitive component revealing the dynamical state of clusters. We propose a new method that can approximately recover the dark matter profile by scaling the BCG+ICL radial profile. Furthermore, we find a recipe for tracing dark matter in unrelaxed clusters by including the most massive satellite galaxies together with the BCG+ICL distribution. Combining the BCG+ICL and the gas distribution enhances the dark matter tracing ability. Our results imply that the BCG+ICL distribution is an effective tracer for the dark matter distribution, and the similarity of the spatial distribution may be a useful probe of the dynamical state of a cluster
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