Terapix Star Formation Region IC 1396, © 2002 CFHT
CFHTLS Release T0001 explanatory table.
by YME YME - Updated June 27th, 2005

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Stacked Images Median of all input images listed in ".lst" file (FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001.lst) , weighted accordingly, and combined using SWarp. Equatorial Coordinate system, J2000 (FK5). Projection: TAN. All images are aligned to the I-band data. Astrometric reference catalog used: USNO-B1. Each image is composed of one single FITS file covering roughly 1deg x 1deg (no more MEF with 36 FITS files; CCDs are no longer singled out after stacking). FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001.fits .

The image are compressed using the RICE algorithm. It produces .fz files that can be uncompressed using the imcopy CFITS/IO tool. See the CADC compression page for details.

Note that the D4-z is not released due to inconsistency between the z-astrometric calibration and the other D4 filters. A D4-z image is available on request to TERAPIX, but without guarantee its follows astrometric specifications to match other D4 images.

Seeing The TERAPIX seeing is defined as twice the median FLUX_RADIUS of a selection of point sources on each CCD. FLUX_RADIUS, as measured by SExtractor, is the radius of the disk that contains 50% of the total flux (it is sometimes called rh in the literature). For a Gaussian profile, the TERAPIX seeing is equal to the Full Width at Half Maximum (FWHM). For a typical MEGACAM Point Spread Function (PSF), the TERAPIX seeing is slightly larger ( 10%) than the true PSF FWHM.
Mag. ZP Photometric calibration is carried out in two steps. In the first step, the photometric solution provided in the header of each image by CFHT (see CFHT page ) is used to re-scale the zero-point of each image to 30.0 (for a one second exposure at zero airmass). In the second step, overlapping sources on all exposures in a given field for a given filter are compared, and the image which has the sources with the highest relative flux (and is therefore the least extincted) is identified and used as a reference image. All other images are then scaled to this image. This absolute calibration is accurate to 0.05 magnitudes, stack-to-stack, based on consideration of stellar colour-colour plots and number counts (see below).

The magnitudes of objects in the final stacks is computed as follows: m=30-2.5log(counts). The magnitude system is instrumental AB

Effective FOV Effective area is derived by subtracting from the MEGACAM fields all the masked areas defined using the .reg mask file. The effective area is same for all filters of a given field.
Chi2 Image Constructed by combining images noted "Y" in the table using "SWarp" (hereafter=filterlist)- Pixel values are actually sqrt(chi2) , not chi2 . There is one Chi2 image per field (joined multi-band image). Chi2 images is generated using the swarp.conf of the co-added images, but with the 'COMBINE_TYPE' chi2' option. FILENAME: CFHTLS_D_chi2[filterlist]_[RA][DEC]_T0001.fits (this file is missing for the D4 fied, since z-band is not released).
Dust map Images E(B-V) FITS images constructed from the E(B-V) images from Schlegel et al , using SWarp, centred and sized according to the I-band images of each deep field. Native Schlegel et al. images have been oversampled, interpolated and transformed into the CFHTLS Equatorial coordinate system using bi-linear interpolation. There is one FITS "dust image" per field, but we DID NOT apply correction to the data. FILENAME: CFHTLS_D_dust_[RA][DEC]_T0001.fits .
Weight map images FITS weight map image. There is one weight map image for each FITS image. Input weight maps are generated during the QualityFITS-in process and output weight maps are produced during the image stacking using SWarp. Weight is defined as the local sky background flux variance. The input weight-maps are generated using the master flat field and mask FITS images delivered by CFHT. When used during co-addition, the weighting scheme takes into account the image-to-image flux rescaling, as described in the SWarp User's manual. FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001_weight.fits .
Completeness Derived by adding simulated stellar objects with a Moffat profile to sub-sections extracted near the center of each stack. Simulated stars have an equivalent FHWM of 1". The x-axis shows the magnitude of the simulated stars, the y-axis shows the fraction of stars which are recovered for each 0.5 magnitude slice. There is one plot per field, and all filters are plotted together. Magnitudes are SExtractor's MAG_AUTO. MAG_AUTO are Kron-like "quasi-total" magnitudes. The typical shift with respect to true "total" magnitudes is 0.06 mag (the flux being slightly underestimated). The magnitude system is instrumental AB. FILENAME: CFHTLS_D_ugriz_[RA][DEC]_T0001_comp.(png/ps) .
Stellar colour-colour Star were selected by automatically locating the stellar branch in the compactness(rh)-magnitude diagram in a serie of 10 arcminute cells distributed over each MEGACAM I-stack; only stars with MAG_AUTO magnitudes in the range [16.5-21.0] mag. have been selected. Magnitude system is instrumental AB.

Stellar tracks from Pickles overplotted for comparison. The Pickles data have not been corrected from atmospheric transmission, so offest between data and stellar tracks are expected. One plot per field and per filter-triplet (hereafter filtertriplet). FILENAME: CFHTLS_D_[filtertriplet]_[RA][DEC]_T0001_diagcc.(png/ps) .

Galaxy counts Galaxy number counts per 0.5 mag., per deg2, computed for the effective area of each field, i.e., after the application of the masks, and derived from the deep catalog produced from the chi2 image. Magnitudes are SExtractor MAG_AUTO. No extinction correction has been applied. The magnitude system is instrumental AB magnitudes; there is one plot per filter. FILENAME: CFHTLS_D_[filter]_galcount_T0001.(png/ps) .
Astrometric quality assessment plots Derived from a pachted version the astrometric software Astrometrix and Photometrix. Internal and external astrometric errors and image-to-image photometric flux rescaling are shown. The astrometric solution derived for each CCD independently using the I-band image that is compared to the USNO-B1 astrometric reference catalog. Other filters calibrated with respect to the I-band astrometric catalog of each deep field. FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001_getRMS[1/2].ps .
.head files ASCII files containing the FITS keywords derived from the astrometric solution found by "Astrometrix" and the FSCALE FITS keyword derived from the photometric rescaling using "Photometrix" (that has to be used in the swarp.conf file : FSCALE_KEYWORD FSCALE) . The .head files can be used to re-SWarp and re-stack FITS images, if needed, without need to run the astrometry software again. FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001_head .
Mask files Built using the "polygon" option of the DS9. visualisation tool to create a "*.reg" file which describes, in world co-ordinates, the regions of the images which should not be used for scientific analysis. Can be used with DS9 (or SAOimage, after they have been transformed to pixel co-ordinates). They mask the MEGACAM field boundary, saturated stars, satellite tracks and image defects, if any. It is an ASCII file: polygons may be added or removed according to user wishes. Note that the masks are constructed using the I-band images which are the references for all filters. so they can be used with the u,g,r and z images. Users who require catalogues selected in other bands (for instance, u or z) many need to make some changes to these masks. FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001.reg .
Catalogs-chi2 These catalogues were produced using SExtractor in dual-image mode, using the gri chisquared image as reference, as well as the weight-map for the final stack. Each catalogue id for each filter for a given field refers to the same object. Note that these catalogues have not been corrected for galactic extinction. For almost all purposes, the Kron-like pseudo-total magnitudes in column 39 gives the best estimate of the object's magnitude (in non-crowded regions). Users who require z- or u- limited catalogues should use these files with caution. FILENAME: CFHTLS_D_[filter]chisq_[RA][DEC]_T0001.cat and CFHTLS_D_[ugriz]chisq_[RA][DEC]_T0001.cat .
Catalogs These catalogues ('.cat' files) were extracted using only the stacked image and the weight map for each filter. Each catalogue id for each filter for a given field refers to a different object. Note that these catalogues have not been corrected for galactic extinction. For almost all purposes, the Kron-like pseudo-total magnitudes in column 39 gives the best estimate of the object's magnitude (in non-crowded regions). Columns of catalogs with '.cat' extentions are defined in the '.param' files. FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001.cat .
Three colour images Produced by combining the stacked FITS images in 3 filters (hereafter: colorlist) using "STIFF". These 2 x 2 binned TIF (in the archive, or PNG on click) colour images are not fully optimised for public outreach posters but only for quality assessment, to check whether colour gradients remain in objects between each filter, in particular far from the centre of the field. FILENAME: CFHTLS_D_[colorlist]_[RA][DEC]_bin22_T0001.tif .
Qfits-in Provide quality assessments produced by QualityFITS on ALL images transferred on TERAPIX disk. Astronomical and technical meta-data regarding each image as well as quality control information are avalaible to all Canadian and French institutes at the restricted access URL Qfits . The list of images selected for the T0001 release and details on each image can then be recovered using the following selection criteria in the front panel: acquisition between June 1st, 2003 and July 22, 2004; seeing <1.1 (except u band <1.4); airmass < 1.4; exposure time >60 sec., TERAPIX quality class A or B. A summary table of selected targets can be saved using the option "Export the whole results in CSV" (ASCII file).

Qfits panels contain 500 x 550 pixels PNG images of each field and their attached weight and background maps, a PSF map image of the field (one PSF model per CCD), histograms of sky background and seeing over each CCD, a preliminary estimate of galaxy and stellar number counts (rough galaxy-star separation, no mask used to avoid defects and very noisy parts of the CCDs in order to use the effective Megacam area. Have a look to the plots of galaxy counts given above that have been done carefully.), with the selected objects shown on rh-mag. diagrams, a summary table (global or for each CCD) with a link to binned 4 x 4 PNG images of each CCD. The PNG field image and its attached weight map are clickable PNG files that provides a 1000 x 1000 resolution PNG image, if needed.

IMPORTANT NOTICE: all qualityFITS-in data products, including individual weight map images attached to each Megacam image, are sent to CADC and available to CFHTLS Users

Qfits-out QualityFITS quality assessments information on final stacked image. Provides similar panels with the same information as Qfits-in described above (except for the PSF map image of the field which has a 10' resolution. A summary FITS table provides information on stacked images . FILENAME: CFHTLS_D_[filter]_[RA][DEC]_T0001_diag.fits.
Files delivered to CADC File list description delivered to CADC and attached to the CFHTLS T0001 release

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