CFHTLenS: The Canada-France-Hawaii Telescope Lensing Survey - Imaging Data and Catalogue Products

TL;DR

This work presents the CFHTLenS imaging data and catalog products derived from the CFHTLS-Wide survey, designed for precise weak lensing analyses with reliable photometric redshifts. It details a patch-level processing pipeline that improves astrometric/photometric homogeneity, including sophisticated masking, PSF modeling, and a cosmic ray handling strategy tailored for lensing measurements. The authors validate external and internal astrometry, quantify photometric accuracy against SDSS, and demonstrate photometric redshift performance via spectroscopic comparisons and large-scale clustering tests. The public release via CADC provides co-added images, weight/mask maps, and catalogues with lensing and photo-$z$ information, underscoring the dataset’s value for weak-lensing studies and informing future surveys like KiDS and DES.

Abstract

We present data products from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg^2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u^*g'r'i'z'. The article presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60-70 mas with respect to SDSS data and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion on the order of 0.01 to 0.03 mag for g'r'i'z' and about 0.04 mag for u^* with respect to SDSS sources down to i <= 21. In the spirit of the CFHTLS all our data products are released to the astronomical community via the Canadian Astronomy Data Centre. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies.

Figures (15)

• Figure 1: Layout of the four CFHTLenS patches. The gray pointings in the W2 region denote fields with incomplete colour coverage. They are not included in the CFHTLenS project. Enclosed areas in W1 and W4 indicate regions of available spectroscopic redshifts for a photometry crosscheck as discussed in Sect. \ref{['sec:specz_comp']}. See text for further details.
• Figure 2: Seeing distributions for all CFHTLenS fields and filters.
• Figure 3: Available data in the W4 patch area: dots denote the centres of primary science observations, crosses indicate the centres of exposures of the astrometric presurvey and triangles mark the centres of additional photometric pegs. The square in the upper left corner shows the MegaPrime field-of-view.
• Figure 4: Quality parameter distributions of all 164 W4 $i'$-band exposures that enter the co-addition and science analysis stage. Shown are the seeing distribution (top left), the distribution of relative photometric zeropoints as determined by scamp (top right), the sky-background brightness in ADU/s (bottom left) and the two components of stellar PSF ellipticities (bottom right). All quantities are estimated as mean values over all 36 chips of a specific exposure. See the text for further details.
• Figure 5: Stellar break in the co-added image of W1m2m1 $i'$-band, with a seeing of $0\hbox{$.\!\!^{\prime\prime}$} 47$: Shown are stellar loci in the size-mag plane (SExtractor quantities FLUX_RADIUS and MAG_AUTO; top panels). The top left panel shows the stellar locus after our standard cosmic-ray removal procedure, the top right panel after we bring back stars whose cores were falsely classified as cosmic rays. The lower panels show corresponding histograms of object counts for $1.4<\hbox{FLUX_RADIUS}<2.0$ and $i'<22.0$. See text for further details.