Information on resource 'CARS survey data'

Images and data from from the CFHTLS archive research survey, a multi-band dataset spanning 37 square degrees of sky in high galactic latitudes.

These services deliver products from the CFHTLS-Archive-Research Survey (CARS). The survey currently offers derived products from 37 sq. degrees of the Wide part from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The main documentation for the products, its creation and its content is the publication 2009A&A...493.1197E. Here, we discuss some points which are not evident from this publication.


For each 1 sq. deg. CARS pointing we currently offer the following products (we discuss them on the example of the CARS pointing W1m0p1); a typical file is named The name contains the following information:

  • W1m0p1 -- name of CARS field under consideration
  • izrgu -- filters involved in the product (here i', r', z', g', u*); for catalogues etc. the first listed filter corresponds to the object detection filter (here 'i'; see also 2009A&A...493.1197E)
  • V1.7A -- internal CARS version number
  • final -- 'final' product

The individual files we offer are:
object catalogue in FITS binary format; beware that they are very big and cumbersome to handle if you do not have efficient tools to work on big FITS binary tables! (typical file size per field: 0.5GB!)
An ASCII version of containing a subset of the most important catalogue quantities. This catalogue should be sufficient for most users. The main content of the catalogue can also be queried in the cat service. (typical gzipped file size per field: 20MB)

An ASCII ds9 region file containing saoimage/ds9 polygon entries (in pixel coordinates). They represent the CARS image masks described in Sect. 3.4 of 2009A&A...493.1197E. Polygons originating from different masking procedures are encoded with different colours (look at expressions such as '# color=yellow' at the end of each line). We offer this file so that interested users can construct own masks containing only parts of our global MASK key. (typical gzipped file size per field: 1MB)

The colour coding in these files is as follows:

  • yellow: masks from our object density analysis and stars identified in the USNO-A2 catalogue
  • green: stars identified in the GSC1 and GSC2 cataogues
  • magenta: masks around extended haloes of bright stars
  • red: masks from our asteroid track analysis


low resolution true colour i', r' and g' JPG image of the CARS field. These images allow a quick look at the data but they are probably not suitable for high-quality poster print-outs. (typical file size per field: 10MB)

low resolution JPG image showing object positions and object masks overlayed on the i'-band image. It allows a quick-look at field-layout and object positions. (typical file size per field: 3MB)

The colour coding in this is:

  • green: areas excluded from scientific analysis by our MASK key
  • yellow: stellar sources (SExtractor CLASS_STAR >=0.95)
  • red: galaxies with high-confidence photo-z estimates: (SExtractor CLASS_STAR < 0.95; reliable object photometry in five bands; BPZ ODDS quality parameter > 0.9); see also Sect. 4 of 2009A&A...493.1197E
  • blue: all other galaxies (SExtractor CLASS_STAR < 0.95)


See 2009A&A...493.1197E, in particular Sect. 4, and the SExtractor Users manual for a description of most catalogue entries. Also see the table notes.


CARS coverage

Services defined within this resource descriptor

Tables defined within this resource descriptor

If you use the CARS products for your own research, please give proper acknowledgment to CADC, the CFHTLS project and the publication 2009A&A...493.1197E

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