68 research outputs found
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
21 cm foreground removal using AI and frequency-difference technique
The deep learning technique has been employed in removing foreground
contaminants from 21 cm intensity mapping, but its effectiveness is limited by
the large dynamic range of the foreground amplitude. In this study, we develop
a novel foreground removal technique grounded in U-Net networks. The essence of
this technique lies in introducing an innovative data preprocessing step
specifically, utilizing the temperature difference between neighboring
frequency bands as input, which can substantially reduce the dynamic range of
foreground amplitudes by approximately two orders of magnitude. This reduction
proves to be highly advantageous for the U-Net foreground removal. We observe
that the HI signal can be reliably recovered, as indicated by the
cross-correlation power spectra showing unity agreement at the scale of Mpc in the absence of instrumental effects. Moreover, accounting for
the systematic beam effects, our reconstruction displays consistent
auto-correlation and cross-correlation power spectrum ratios at the
level across scales Mpc, with only a 10% reduction
observed in the cross-correlation power spectrum at Mpc. The
effects of redshift-space distortion are also reconstructed successfully, as
evidenced by the quadrupole power spectra matching. In comparison, our method
outperforms the traditional Principal Component Analysis method, which derived
cross-correlation ratios are underestimated by around 75%. We simulated various
white noise levels in the map and found that the mean cross-correlation ratio
when the level of the thermal noise is
smaller than or equal to that of the HI signal. We conclude that the proposed
frequency-difference technique can significantly enhance network performance by
reducing the amplitude range of foregrounds and aiding in the prevention of HI
loss.Comment: 18 pages, 16 figure
Weak Lensing Reconstruction by Counting DECaLS Galaxies
Alternative to weak lensing measurements through cosmic shear, we present a
weak lensing convergence map reconstructed through cosmic
magnification effect in DECaLS galaxies of the DESI imaging surveys DR9. This
is achieved by linearly weighing maps of galaxy number overdensity in
different magnitude bins of photometry bands. The weight is designed to
eliminate the mean galaxy deterministic bias, minimize galaxy shot noise while
maintaining the lensing convergence signal. We also perform corrections of
imaging systematics in the galaxy number overdensity. The map
has deg sky coverage. Given the low number density of DECaLS
galaxies, the map is overwhelmed by shot noise and the map
quality is difficult to evaluate using the lensing auto-correlation.
Alternatively, we measure its cross-correlation with the cosmic shear catalogs
of DECaLS galaxies of DESI imaging surveys DR8, which has deg
overlap in sky coverage with the map. We detect a
convergence-shear cross-correlation signal with . The analysis
also shows that the galaxy intrinsic clustering is suppressed by a factor
and the residual galaxy clustering contamination in the
map is consistent with zero. Various tests with different galaxy
and shear samples, and the Akaike information criterion analysis all support
the lensing detection. So is the imaging systematics corrections, which enhance
the lensing signal detection by . We discuss various issues for
further improvement of the measurements
The Intensity of Diffuse Galactic Emission Reflected by Meteor Trails
We calculate the reflection of diffuse galactic emission by meteor trails and
investigate its potential relationship to Meteor Radio Afterglow (MRA). The
formula to calculate the reflection of diffuse galactic emission is derived
from a simplified case, assuming that the signals are mirrored by the
cylindrical over-dense ionization trail of meteors. The overall observed
reflection is simulated through a ray tracing algorithm together with the
diffuse galactic emission modelled by the GSM sky model. We demonstrate that
the spectrum of the reflected signal is broadband and follows a power law with
a negative spectral index of around -1.3. The intensity of the reflected signal
varies with local sidereal time and the brightness of the meteor and can reach
2000 Jy. These results agree with some previous observations of MRAs.
Therefore, we think that the reflection of galactic emission by meteor trails
can be a possible mechanism causing MRAs, which is worthy of further research.Comment: 15 pages, 10 figures, 2 tables, accepted for publication in MNRAS,
10.1093/mnras/stad342
Noisy weak-lensing convergence peak statistics near clusters of galaxies and beyond
Taking into account noise from intrinsic ellipticities of source galaxies, in
this paper, we study the peak statistics in weak-lensing convergence maps
around clusters of galaxies and beyond. We emphasize how the noise peak
statistics is affected by the density distribution of nearby clusters, and also
how cluster-peak signals are changed by the existence of noise. These are the
important aspects to be understood thoroughly in weak-lensing analyses for
individual clusters as well as in cosmological applications of weak-lensing
cluster statistics. We adopt Gaussian smoothing with the smoothing scale
in our analyses. It is found that the noise peak
distribution near a cluster of galaxies depends sensitively on the density
profile of the cluster. For a cored isothermal cluster with the core radius
, the inner region with appears noisy containing on average
peaks with for and the true peak
height of the cluster , where denotes the convergence signal to
noise ratio. For a NFW cluster of the same mass and the same central , the
average number of peaks with within is . Thus a
high peak corresponding to the main cluster can be identified more cleanly in
the NFW case. In the outer region with , the number of high
noise peaks is considerably enhanced in comparison with that of the pure noise
case without the nearby cluster. (abridged)Comment: 10 figures, ApJ in pres
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
Void Lensing in Cubic Galileon Gravity
Weak lensing studies via cosmic voids are a promising probe of Modified
Gravity (MG). Excess surface mass density (ESD) is widely used as a lensing
statistic in weak lensing research. In this paper, we use the ray-tracing
method to study the ESD around voids in simulations based on Cubic Galileon
(CG) gravity. With the compilation of N-body simulation and ray-tracing method,
changes in structure formation and deflection angle resulting from MG can both
be considered, making the extraction of lensing signals more realistic. We find
good agreements between the measurement and theoretical prediction of ESD for
CG gravity. Meanwhile, the lensing signals are much less affected by the change
of the deflection angle than the change of the structure formation, indicating
a good approximation of regarding ESD (statistics) as the projection of 3D dark
matter density field. Finally, we demonstrate that it is impossible to
distinguish CG and General Relativity in our simulation, however, in the
next-generation survey, thanks to the large survey area and the increased
galaxy number density, detecting the differences between these two models is
possible. The methodology employed in this paper that combines N-body
simulation and ray-tracing method can be a robust way to measure the lensing
signals from simulations based on the MGs, and especially on that which
significantly modifies the deflection angle.Comment: 14 pages, 9 figure
CSST forecast: impact from non-Gaussian covariances and requirements on systematics-control
The precise estimation of the statistical errors and accurate removal of the
systematical errors are the two major challenges for the stage IV cosmic shear
surveys. We explore their impact for the China Space-Station Telescope (CSST)
with survey area up to redshift . We consider
statistical error contributed from Gaussian covariance, connected non-Gaussian
covariance and super-sample covariance. We find the super-sample covariance can
largely reduce the signal-to-noise of the two-point statistics for CSST,
leading to a loss in the figure-of-merit for the matter clustering
properties ( plane) and in the dark energy
equation-of-state ( plane). We further put requirements of
systematics-mitigation on: intrinsic alignment of galaxies, baryonic feedback,
shear multiplicative bias, and bias in the redshift distribution, for an
unbiased cosmology. The to level requirements emphasize
strong needs in related studies, to support future model selections and the
associated priors for the nuisance parameters.Comment: submitted to MNRA
Validity of patients' online reviews at direct-to-consumer teleconsultation platforms:a protocol for a cross-sectional study using unannounced standardised patients
- …