[Paper Review] The VIRMOS deep imaging survey: I. overview and survey strategy

O. Le Fèvre, Y. Mellier+12 more|ArXiv.org|Jun 12, 2003

Astronomy and Astrophysical ResearchPhysics and Astronomy89 citations

TL;DR

This paper presents the CFH12K-VIRMOS deep imaging survey, a multi-band (B, V, R, I) imaging survey covering 17 deg² across four high-galactic-latitude fields using the CFH12K camera on the Canada-France-Hawaii Telescope. It delivers photometric catalogs of 2.175 million objects with I_AB = 24.8 (wide) and I_AB = 25.3 (deep) depth, enabling studies of high-redshift galaxies, weak lensing, and large-scale structure, with data released for general use starting July 1, 2003.

ABSTRACT

This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging survey in four fields totalling more than 17 deg^2, conducted with the 30x40 arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose survey used for a variety of science goals, including surveys of very high redshift galaxies and weak lensing studies. Four high galactic latitude fields, each 2x2 deg^2, have been selected along the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively. The data is pipeline processed at the Terapix facility at the Institut d'Astrophysique de Paris to produce large mosaic images. The catalogs produced contain the positions, shape, total and aperture magnitudes for the 2.175 million objects. The depth measured (3sigma in a 3 arc-second aperture) is I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful quality control has been applied on the data as described in joint papers. These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a large spectroscopic survey of the distant universe (Le Fèvre et al., 2003). First results from the CFH12K-VIRMOS survey have been published on weak lensing (e.g. van Waerbeke & Mellier 2003). Catalogs and images are available through the VIRMOS database environment under Oracle ({ t http://www.oamp.fr/virmos}). They will be open for general use on July 1st, 2003.

Motivation & Objective

• To conduct a deep, wide-area multi-band imaging survey to support diverse cosmological and astrophysical studies.
• To enable the selection of targets for the VIRMOS-VLT Deep Survey, a large spectroscopic redshift survey of distant galaxies.
• To produce high-accuracy photometric and astrometric catalogs for weak lensing and galaxy clustering studies.
• To provide a public data set for the broader astronomical community to study high-redshift galaxies, dark matter, and large-scale structure.

Proposed method

• The survey used the CFH12K camera on the Canada-France-Hawaii Telescope to image four 2×2 deg² fields along the celestial equator.
• Exposure times ranged from 1 to 7 hours in B, V, R, and I bands, with deeper integration in the 0226-04 field for the 'deep' area.
• Pipeline processing was performed at the Terapix facility at the Institut d'Astrophysique de Paris to produce calibrated mosaic images and photometric catalogs.
• Photometry and astrometry were validated through cross-CCD comparisons, USNO star cross-matches, and color consistency checks with stellar loci.
• Quality control included monitoring photometric zero points via the Elixir queue program and assessing angular correlation functions.
• Data were stored in an Oracle-based database with user-selectable queries for magnitudes, colors, positions, and shapes.

Experimental results

Research questions

• RQ1 What is the distribution and evolution of high-redshift galaxies (z ≈ 5) in deep optical imaging?
• RQ2 How accurately can weak lensing signatures of large-scale structure be measured in a deep, wide-area imaging survey?
• RQ3 What is the fidelity and systematics level of photometric and astrometric measurements in large mosaic images from a 30×40 arcmin² camera?
• RQ4 How do galaxy shapes and clustering properties relate to dark matter distribution in the distant universe?
• RQ5 Can the survey data effectively select targets for a large spectroscopic redshift survey of galaxies up to z ≈ 5?

Key findings

• The survey covers more than 17 deg², with 16 deg² in 'wide' fields and 1.3×1 deg² in a 'deep' area centered on the 0226-04 field.
• The 3σ detection depth is I_AB = 24.8 in the wide areas and I_AB = 25.3 in the deep area, using a 3 arcsecond aperture.
• A total of 2.175 million objects were detected in the I band, with 1.15 million in the magnitude range 17.5 ≤ I_AB ≤ 24.
• Photometric accuracy is better than 0.1 magnitudes, with color errors less than 0.1 mag for bright stars.
• Astrometric accuracy was validated against the USNO catalog, with positional errors consistent with expected systematics.
• The survey has already enabled cosmic shear measurements and constraints on cosmological parameters such as Ω_m and σ_8, demonstrating data quality and scientific utility.