75 research outputs found
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
Forecast of cross-correlation of CSST cosmic shear tomography with AliCPT-1 CMB lensing
We present a forecast study on the cross-correlation between cosmic shear
tomography from the Chinese Survey Space Telescope (CSST), and CMB lensing from
Ali CMB Polarization Telescope (AliCPT-1) in Tibet. We generate the correlated
galaxy lensing and CMB lensing signals from the Gaussian realizations based on
the inputted auto- and cross-spectra. As for the error budget, we consider the
CMB lensing reconstruction noise based on the AliCPT-1 lensing reconstruction
pipeline; the shape noise of the galaxy lensing measurement; CSST photo-
error; photo- bias; intrinsic alignment effect. The AliCPT-1 CMB lensing
mock data are generated according to two experimental stages, namely the "4
modules*yr" and "48 modules*yr" cases. We estimate the cross-spectra in 4
tomographic bins according to the CSST photo- distribution in the range of
. After reconstructing the pseudo-cross-spectra from the
realizations, we calculate the signal-to-noise ratio (SNR). By combining the 4
photo-z bins, the total cross-correlation SNR (AliCPT-1 "4
modules*yr") and SNR (AliCPT-1 "48 modules*yr"). Finally, we study
the cosmological application of this cross-correlation signal. Due to the
negative contribution to the galaxy lensing data, the exclusion of intrinsic
alignment in the template fitting will lead to roughly a
increasement in but without changing the value. For AliCPT-1
first and second stages, the cross-correlation of CSST cosmic shear with CMB
lensing give and and
and , respectively.Comment: 17 pages, 10 figure
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
How to coadd images: II. Anti-aliasing and PSF deconvolution
We have developed a novel method for co-adding multiple under-sampled images
that combines the iteratively reweighted least squares and divide-and-conquer
algorithms. Our approach not only allows for the anti-aliasing of the images
but also enables PSF deconvolution, resulting in enhanced restoration of
extended sources, the highest PSNR, and reduced ringing artefacts. To test our
method, we conducted numerical simulations that replicated observation runs of
the CSST/VST telescope and compared our results to those obtained using
previous algorithms. The simulation showed that our method outperforms previous
approaches in several ways, such as restoring the profile of extended sources
and minimizing ringing artefacts. Additionally, because our method relies on
the inherent advantages of least squares fitting, it is more versatile and does
not depend on the local uniformity hypothesis for the PSF. However, the new
method consumes much more computation than the other approaches.Comment: 16 pages, 5 figures, 2 tables, accepted for publishing on RA
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