75 research outputs found

    Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts

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    We present our deep YY-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 z>2.2z>2.2, 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 YY-band data with the CFHTLenS u∗g′r′i′z′u^*g'r'i'z' optical data and UKIDSS DXS JHKJHK near-infrared data. With JJ-band image as reference total ∼\sim80,000 galaxies are detected in the final mosaic down to YY-band 5σ5\sigma point source limiting depth of 22.86 mag. Compared with the ∼\sim3500 spectroscopic redshifts, our photometric redshifts for galaxies with z<1.5z<1.5 and i′≲24.0i'\lesssim24.0 mag have a small systematic offset of ∣Δz∣≲0.2|\Delta{z}|\lesssim0.2, 1σ\sigma scatter 0.03<σΔz<0.060.03<\sigma_{\Delta z} < 0.06, and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS photometric redshifts, and find that ours are more reliable at z≳0.6z\gtrsim0.6 because of the inclusion of the near-infrared bands. In particular, including the YY-band data can improve the accuracy at z∼1.0−2.0z\sim 1.0-2.0 because the location of the 4000\AA-break is better constrained. The YY-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

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    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-zz error; photo-zz 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-zz distribution in the range of z∈[0,4)z\in[0,4). 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≈17\approx17 (AliCPT-1 "4 modules*yr") and SNR≈26\approx26 (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 0.6σ0.6\sigma increasement in σ8\sigma_8 but without changing the S8S_8 value. For AliCPT-1 first and second stages, the cross-correlation of CSST cosmic shear with CMB lensing give σ8=0.770±0.034\sigma_8=0.770\pm 0.034 and S8=0.797±0.028S_8=0.797\pm 0.028 and σ8=0.801±0.023\sigma_8=0.801\pm 0.023 and S8=0.813±0.016S_8=0.813\pm 0.016, respectively.Comment: 17 pages, 10 figure

    HybPSF: Hybrid PSF reconstruction for the observed JWST NIRCam image

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    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

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    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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