69 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
Deep CFHT Y-band Imaging of VVDS-F22 Field: II. Quasar Selection and Quasar Luminosity Function
We report the result of a faint quasar survey in a one square degree field.
The aim is to test the Y-K/g-z and J-K/i-Y color selection criteria for quasars
at faint magnitude, to obtain a complete sample of quasars based on deep
optical and near-infrared color-color selection, and to measure the faint end
of quasar luminosity function (QLF) over a wide redshift range. We carried out
a quasar survey based on the Y-K/g-z and J-K/i-Y quasar selection criteria,
using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a
two-degree field within the F22 field of the VIMOS VLT deep survey, optical
co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared
data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered
25 new quasars at 0.5 < z < 4.5 and i < 22.5 mag within one square degree
field. The survey significantly increases the number of faint quasars in this
field, especially at z ~ 2-3. It confirms that our color selections are highly
complete in a wide redshift range (z < 4.5), especially over the quasar number
density peak at z ~ 2-3, even for faint quasars. Combining all previous known
quasars and new discoveries, we construct a sample with 109 quasars, and
measure the binned QLF and parametric QLF. Although the sample is small, our
results agree with a pure luminosity evolution at lower redshift and luminosity
evolution and density evolution model at redshift z > 2.5.Comment: 14 pages, 10 figures, accepted by A
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