125 research outputs found
Is the large-scale structure traced by the BOSS LOWZ galaxies consistent with ?
Recently, several studies reported a significant discrepancy between the
clustering and lensing of the Baryon Oscillation Spectroscopic Survey (BOSS)
galaxies in the cosmology. We construct a simple yet powerful
model based on the linear theory to assess whether this discrepancy points
toward deviations from . Focusing on scales
, we model the amplitudes of clustering and lensing of BOSS
LOWZ galaxies using three parameters: galaxy bias , galaxy-matter
cross-correlation coefficient , and , defined as the ratio
between the true and values of . Using the
cross-correlation matrix as a diagnostic, we detect systematic uncertainties
that drive spurious correlations among the low-mass galaxies. After building a
clean LOWZ sample with , we derive a joint constraint of
and from clustering+lensing, yielding
and , i.e., a
tension with . However, due to the strong degeneracy
between and , systematic uncertainties in
could masquerade as a tension with . To ascertain this possibility, we
develop a new method to measure from the cluster-galaxy
cross-correlation and cluster weak lensing using an overlapping cluster sample.
By applying the independent bias measurement () as a
prior, we successfully break the degeneracy and derive stringent constraints of
and . Therefore, our result
suggests that the large-scale clustering and lensing of LOWZ galaxies are
consistent with , while the different bias estimates may be
related to some observational systematics in the target selection.Comment: 8 pages, 5 figures, comments welcome
Relieving the Tension: Exploring the Surface-type DBI Model as a Dark Matter Paradigm
Recent observations of weak gravitational lensing surveys indicate a smoother
Universe compared to the predictions of the Cosmic Microwave Background (CMB).
This is known as tension or tension, where
represents the present root-mean-square matter fluctuation averaged over a
sphere of radius and . In this letter, we investigate a kind of general
Dirac-Born-Infeld (DBI) Lagrangian referred as surface-type DBI (s-DBI) model.
We have found that, up to the linear order, the constraints on the s-DBI model
with CMB from Planck2018 and low-redshift probes (WL and GC) yield and , respectively,
which are not only self-consistent but also consistent with the values derived
from most low-redshift probes. Furthermore, we provide an outlook for searching
the non-linear effects of this model, which could be helpful to resolve other
issues by Cold Dark Matter on small scales.Comment: Submitted, comments welcom
An analytic model for non-spherical lenses in covariant MOdified Newtonian Dynamics
Strong gravitational lensing by galaxies in MOdified Newtonian Dynamics
(MOND) has until now been restricted to spherically symmetric models. These
models were able to account for the size of the Einstein ring of observed
lenses, but were unable to account for double-imaged systems with collinear
images, as well as four-image lenses. Non-spherical models are generally
cumbersome to compute numerically in MOND, but we present here a class of
analytic non-spherical models that can be applied to fit double-imaged and
quadruple-imaged systems. We use them to obtain a reasonable MOND fit to ten
double-imaged systems, as well as to the quadruple-imaged system Q2237+030
which is an isolated bulge-disc lens producing an Einstein cross. However, we
also find five double-imaged systems and three quadruple-imaged systems for
which no reasonable MOND fit can be obtained with our models. We argue that
this is mostly due to the intrinsic limitation of the analytic models, even
though the presence of small amounts of additional dark mass on galaxy scales
in MOND is also plausible.Comment: 10 pages, 6 figures, references update
Mass-concentration relation of clusters of galaxies from CFHTLenS
Based on weak lensing data from the Canada-France-Hawaii Telescope Lensing
Survey (CFHTLenS), in this paper we study the mass-concentration (-)
relation for redMaPPer clusters in the fields. We extract the
- relation by measuring the density profiles of individual clusters
instead of using stacked weak lensing signals. By performing Monte Carlo
simulations, we demonstrate that although the signal-to-noise ratio for each
individual cluster is low, the unbiased - relation can still be reliably
derived from a large sample of clusters by carefully taking into account the
impacts of shape noise, cluster center offset, dilution effect from member or
foreground galaxies, and the projection effect. Our results show that within
error bars the derived - relation for redMaPPer clusters is in agreement
with simulation predictions. There is a weak deviation in that the halo
concentrations calibrated by Monte Carlo simulations are somewhat higher than
that predicted from cosmology.Comment: Accepted for Publication in ApJ. 18 pages, 8 figures. Updated to
match the published versio
Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts
We present our deep -band imaging data of a two square degree field within
the F22 region of the VIMOS VLT Deep Survey. The observations were conducted
using the WIRCam instrument mounted at the Canada--France--Hawaii Telescope
(CFHT). The total on-sky time was 9 hours, distributed uniformly over 18 tiles.
The scientific goals of the project are to select faint quasar candidates at
redshift , and constrain the photometric redshifts for quasars and
galaxies. In this paper, we present the observation and the image reduction, as
well as the photometric redshifts that we derived by combining our -band
data with the CFHTLenS optical data and UKIDSS DXS
near-infrared data. With -band image as reference total 80,000
galaxies are detected in the final mosaic down to -band point
source limiting depth of 22.86 mag. Compared with the 3500 spectroscopic
redshifts, our photometric redshifts for galaxies with and
mag have a small systematic offset of
, 1 scatter ,
and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS
photometric redshifts, and find that ours are more reliable at
because of the inclusion of the near-infrared bands. In particular, including
the -band data can improve the accuracy at because the
location of the 4000\AA-break is better constrained. The -band images, the
multi-band photometry catalog and the photometric redshifts are released at
\url{http://astro.pku.edu.cn/astro/data/DYI.html}.Comment: 16 pages, 12 figures, 4 tables. AJ accepted. Updated access to the
data: https://zenodo.org/record/140003
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
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
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