Canada-France-Hawaii Telescope
Legacy Survey


Last update: Thu Jun 27 22:38:49 HST 2019

CFHTLS Overview

Canada and France joined a large fraction of their dark and grey telescope time from mid-2003 to early 2009 for a large project, the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data acquisition and calibration have been a major undertaking for the Canadian and French communities: more than 2300 hours over 5 years (an equivalent of 450 nights) have been devoted to the survey using the wide field optical imaging camera MegaCam, a 1 degree by 1 degree field of view 340 Megapixel camera. The survey has already generated a large number of exciting scientific results.

Final Public Data Release

2012 is marked by the delivery of the final official release of the CFHTLS data set (October 26, see the press release here). With the aim of ensuring the legacy of the survey, the Terapix CFHTLS T0007 release of finely calibrated stacks and catalogs is available to the worldwide community at the Canadian Astronomy Data Centre (CADC). For this final release, the collaboration between Terapix, CFHT and the SNLS team brought significant gains on the global photometric calibration (internal & external). The T0007 based photometric redshifts for the Wide survey produced by the Laboratoire d'Astrophysique de Marseille (LAM) in collaboration with Terapix are also immediately publicly available. In addition, searchable catalogues are made available at the Centre de Données astronomiques de Strasbourg (CDS) through VizieR while the entire survey can now be explored visually through the Aladin sky atlas. The technical documentation for the final CFHTLS release by Terapix can be consulted here (PDF). For those interested in the individual MegaCam frames making the CFHTLS collection, the 22,000+ MegaCam images pre-processed and calibrated by Elixir at CFHT are also available to the worldwide community at the CADC.

Please note the acknowledgment text for publications when using CFHTLS data.

From the Solar System to the distant Universe

The CFHTLS has three distinct survey components, from ultra deep pencils to deep wide patches, to very wide shallow areas:

The supernovae survey and the deep survey: SNLS and the "Deep"

Covering 4 square degrees in four independent fields spread across the sky to have two fields visible throughout a given night at any time of the year, and acquired through the whole filter set (u*, g', r', i', z') with integration times ranging from 33 to 132 hours depending on the filter (u*: 33, g':33, r':66, i':132, z':66), this survey was sequenced over 5 years for the SuperNovae Legacy Survey (SNLS): aimed mainly at the detection and monitoring of as many as 500 type Ia supernovae and at the study of the galaxy distribution on images reaching r'=28, this survey is leading to a better understanding of the early Universe as well as a the determination of the dark energy parameters with an unprecedented accuracy. The galaxies and quasars constitute statistical samples bringing strong constraints on galaxy evolution and global star formation history. Thanks to the time sequencing, transient phenomena and moving objects can be detected, providing a unique monitoring over five years of fields at various galactic and ecliptic latitudes.

A wide synoptic survey, the "Wide"

Covering 155 square degrees in four patches of 25 to 72 square degrees through the whole filter set (u*, g', r', i', z') down to i'=24.5, this survey allows the study of the large scale structures and matter distribution in the Universe through weak lensing and galaxy distribution, as well as the study of clusters of galaxies through morphology and photometric properties of galaxies. All fields are to be used for stellar population investigations and searched for moving objects and transient phenomena.

A very wide shallow survey, the "Very Wide"

Covering a large fraction of the ecliptic plane inside a band of +/-2 degrees for a total area of 410 square degrees, this survey provides an unprecedented sample of the solar system population beyond Neptune. This data set provided discoveries that challenge the currently discussed models of the solar system formation. CFHTLS-VW was conducted in 3 colors (g', r', i') to create a new stellar data set for studies related to stellar populations (including white and brown dwarfs), as well as structures & dynamics of our Galaxy.

Survey Organization

The three main entities that served the Canadian and French communities were 1) the CFHT for the data acquisition, pre-processing and calibration, 2) Terapix (based at the Institut d'Astrophysique de Paris) for the data ressampling and stacking, fine astrometric and photometric calibration, and source catalogs generation, 3) the Canadian Astronomy Data Centre (CADC, based in Victoria) for all activities related to the archiving and release of the various data products to the scientific community.

The Canada-France-Hawaii Telescope Legacy Survey was organized and monitored by a Steering Group, and technically supported by a Data Oversight Group, under the supervision of the CFHT Scientific Advisory Council (SAC). The CFHT Board of Executives gave its final approval for the project in 2002 following a SAC recommendation prepared at its May 2002 meeting. Various reports and recommendations have been written over the course of the year 2001 by the Steering Group and, though a bit dated today, they still contain the core rational for the survey. The documents are presented here.