151 research outputs found
Negative Energies and a Constantly Accelerating Flat Universe
It has been shown that in the context of General Relativity (GR) enriched
with a new set of discrete symmetry reversal conjugate metrics, negative energy
states can be rehabilitated while avoiding the well-known instability issues.
We review here some cosmological implications of the model and confront them
with the supernovae and CMB data. The predicted flat universe constantly
accelerated expansion phase is found to be in rather good agreement with the
most recent cosmological data
DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions
We present a novel parameter-free cosmological void finder (\textsc{dive},
Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which
efficiently computes the empty spheres constrained by a discrete set of
tracers. We define the spheres as DT voids, and describe their properties,
including an universal density profile together with an intrinsic scatter. We
apply this technique on 100 halo catalogues with volumes of 2.5\,Gpc
side each, with a bias and number density similar to the BOSS CMASS Luminous
Red Galaxies, performed with the \textsc{patchy} code. Our results show that
there are two main species of DT voids, which can be characterised by the
radius: they have different responses to halo redshift space distortions, to
number density of tracers, and reside in different dark matter environments.
Based on dynamical arguments using the tidal field tensor, we demonstrate that
large DT voids are hosted in expanding regions, whereas the haloes used to
construct them reside in collapsing ones. Our approach is therefore able to
efficiently determine the troughs of the density field from galaxy surveys, and
can be used to study their clustering. We further study the power spectra of DT
voids, and find that the bias of the two populations are different,
demonstrating that the small DT voids are essentially tracers of groups of
haloes.Comment: 12 pages, 13 figure
Results of the Saclay NaI(Tl) WIMP search experiment and comparison with other NaI(Tl) experiments
Pulse shape discrimination and Dark Matter Search with NaI(Tl) Scintillator at the Laboratoire Souterrain de Modane
Linear redshift space distortions for cosmic voids based on galaxies in redshift space
Cosmic voids found in galaxy surveys are defined based on the galaxy
distribution in redshift space. We show that the large scale distribution of
voids in redshift space traces the fluctuations in the dark matter density
field \delta(k) (in Fourier space with \mu being the line of sight projected
k-vector): \delta_v^s(k) = (1 + \beta_v \mu^2) b^s_v \delta(k), with a beta
factor that will be in general different than the one describing the
distribution of galaxies. Only in case voids could be assumed to be quasi-local
transformations of the linear (Gaussian) galaxy redshift space field, one gets
equal beta factors \beta_v=\beta_g=f/b_g with f being the growth rate, and b_g,
b^s_v being the galaxy and void bias on large scales defined in redshift space.
Indeed, in our mock void catalogs we measure void beta factors being in good
agreement with the galaxy one. Further work needs to be done to confirm the
level of accuracy of the beta factor equality between voids and galaxies, but
in general the void beta factor needs to be considered as a free parameter for
RSD studies.Comment: 10 pages, 9 figures; matches the version accepted by PR
Observational constraints on cosmic neutrinos and dark energy revisited
Using several cosmological observations, i.e. the cosmic microwave background
anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements
of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational
Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the
HST prior, we impose constraints on the sum of neutrino masses (\mnu), the
effective number of neutrino species (\neff) and dark energy equation of
state (), individually and collectively. We find that a tight upper limit on
\mnu can be extracted from the full data combination, if \neff and are
fixed. However this upper bound is severely weakened if \neff and are
allowed to vary. This result naturally raises questions on the robustness of
previous strict upper bounds on \mnu, ever reported in the literature. The
best-fit values from our most generalized constraint read
\mnu=0.556^{+0.231}_{-0.288}\rm eV, \neff=3.839\pm0.452, and
at 68% confidence level, which shows a firm lower limit on
total neutrino mass, favors an extra light degree of freedom, and supports the
cosmological constant model. The current weak lensing data are already helpful
in constraining cosmological model parameters for fixed . The dataset of
Hubble parameter gains numerous advantages over supernovae when ,
particularly its illuminating power in constraining \neff. As long as is
included as a free parameter, it is still the standardizable candles of type Ia
supernovae that play the most dominant role in the parameter constraints.Comment: 39 pages, 15 figures, 7 tables, accepted to JCA
Halo mass distribution reconstruction across the cosmic web
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedWe study the relation between halo mass and its environment from a probabilistic perspective. We find that halo mass depends not only on local dark matter density, but also on non-local quantities such as the cosmic web environment and the halo- exclusion effect. Given these accurate relations, we have developed the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits us to assign halo masses to a distribution of haloes in three-dimensional space. This can be ap- plied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for diferent mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark N-body simulation: the power spectra are within 1-_ up to scales of k = 0:2 hMpc-1, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, we finnd evidence of the halo- exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. We also compute the 2- and 3-point correlation functions, and find an excellent agreement with N-body results. Our work represents a quantitative application of the cosmic web classification. It can have fur- ther interesting applications in the multi-tracer analysis of the large-scale structure for future galaxy surveysCZ and CT acknowledge support from Tsinghua University, and 973 program No. 2013CB834906. FP were supported by the Spanish MICINNs Consolider-Ingenio 2010 Programme under grant MultiDark CSD2009-00064 and AYA2010-21231-C02-01 grant, the Comunidad de Madrid under grant HEPHACOS S2009/ESP-1473, and Spanish MINECOs Centro de Excelencia Severo Ochoa Programme under grant SEV-2012-0249.
GY acknowledges support from the Spanish MINECO under research grants AYA2012-31101, FPA2012-34694 and Consolider Ingenio SyeC CSD2007-005
HybPSF: Hybrid PSF reconstruction for the observed JWST NIRCam image
The James Webb Space Telescope (JWST) ushers in a new era of astronomical
observation and discovery, offering unprecedented precision in a variety of
measurements such as photometry, astrometry, morphology, and shear measurement.
Accurate point spread function (PSF) models are crucial for many of these
measurements. In this paper, we introduce a hybrid PSF construction method
called HybPSF for JWST NIRCam imaging data. HybPSF combines the WebbPSF
software, which simulates the PSF for JWST, with observed data to produce more
accurate and reliable PSF models. We apply this method to the SMACS J0723
imaging data and construct supplementary structures from residuals obtained by
subtracting the WebbPSF PSF model from the data. Our results show that HybPSF
significantly reduces discrepancies between the PSF model and the data compared
to WebbPSF. Specifically, the PSF shape parameter ellipticity and size
comparisons indicate that HybPSF improves precision by a factor of
approximately 10 for \$R^2\$ and \$50\%\$ for \$e\$. This improvement has
important implications for astronomical measurements using JWST NIRCam imaging
data
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