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CFHTLS T0004 Wide and Deep summary
Last content update July 17th, 2007

TERAPIX T0004 release : overview of Deep + Wide data
Release reference identification : T0004 - June 2007: Release date July 3.


Content of the Terapix T0004 pages:

- Latest news, June 24 (Public worldwide): get the T0004 Deep+Wide photo-z catalogues (Coupon et al (2009))

1. T0004 quick summary table : exp. time, precise effective area, u-band Obs. Date

2. T0004 Synopic Table : explanatory table

3. T0004 Synoptic Table : short description and access point

4. T0004 : astrometric and photometric calibration

5. CFHTLS / SDSS comparison

6. Terapix T0004 file naming convention

7. CFHTLS T0004: catalogue parameters

8. The CFHTLS Data Access Policy

9. Acknowledgement


Most important new features as compared to T0003

-  2 series of Deep data :

. 25% best seeing images stack (D25: ugriz with seeing down to 0.60" for some fields with exp. time up to 15hrs) and

. 85% best seeing images stack : the deepest wide field ever produced with a 4-meter telescope (D85: up to 50 hrs in some fields)

-  Addition of the W4 wide field with 11 deg2 complete in ugriz

-  New astrometry: done with 2MASS instead of USNO. More accurate and more stable astrometric calibration than T0003 for ALL fields.

CFHTLS T0004 target lists:

-  Deep fields with 25% best seeing images: D1-25, D2-25, D3-25 and D4-25
-  Deep fields with 85% best seeing images: D1-85, D2-85, D3-85 and D4-85
-  Wide fields: W1, W2, W3 and W4

-  Positions of Deep and Wide fields in the sky.

Image selection criteria for the stacking process:
-  Data obtained between: June 1st, 2003 and Oct. 24, 2006.
-  Terapix Class : A or B
-  Exp. time: > 60 sec.
-  Seeing : < 1.3" , except for u* (<1.4")
-  Airmass: < 1.7
-  Skyprobe value: <2.0 Mag. (security limit)

Overview of T0004 stacks and status of the CFHTLS-T0004 sky coverage

-  Number of Deep stacks: 40 (20 D25+20 D85)
-  Number of Wide stacks: 524 (35 u, 133 g, 173 r, 137 i, 46 z)
-  Filter distribution of wides:

Wide field gri onlygriz onlyall ugrizall gri (=chi2) Total u/g/r/i/ or z
W1241194473
W219102038
W328854149
W441111616
Total751135121176

W1-ugriz -T0004 sky coverage W2-ugriz -T0004 sky coverage W3-ugriz -T0004 sky coverage W4-ugriz -T0004 sky coverage

Quick T0004 stack summary table and printable table The Synopic T0004 Table

Overview photometry:

-  Magnitudes: AB Megacam instrumental system
-  Mag. zero points : The zero points of all images are set to 30 AB magnitudes. The images have an effective exposure time of one second.
-  SDSS/CFHTLS transformations resulting from the SNLS group (Regnault et al. ):

. uCFHTLS - uSDSS = -0.214 * (u-g)SDSS

. gCFHTLS - gSDSS = -0.156 * (g-r)SDSS

. rCFHTLS - rSDSS = -0.000 * (g-r)SDSS

. iCFHTLS - iSDSS = -0.094 * (r-i)SDSS

. zCFHTLS - zSDSS = +0.050 * (i-z)SDSS

-  Mean rms external errors with respect to SDSS (when available): 0.02 mag. , but depends on the field and the filter.

-  Common fields between T0003 and T0004 show the same results, as demonstrated from the stellar color-color plots and past SDSS comparisons.

WARNING: there are several fields with an offset in u*-band. . The stability of results obtained on common fields between T0003 and T0004 shows it is likely a photometric calibration problem, leading to wrong ZPs . CFHT is looking for this. The files are listed elsewhere.

A detailed CFHTLS/SDSS comparison.

Overview astrometry

-  Calibration catalogue: 2MASS. For each patch (D1, D2, D3, D4, W1, W2, W3, W4), all CFHTLS images located in the field with exp. time >180s. , airmass <1.7 and seeing<1.5" have been used to set the astrometric calibration of each field used later for the stacks.

-  Mean rms external error with respect to 2MASSS: 0.24"+/-0.02" in both directions (instead of 0.42" in previous releases using USNO-B, with significant anisotropy)).

-  Mean rms internal error is 0.017"+/-0.002" in both directions (instead of 0.035" before).

-  Mean systematic offset of stacks with respect to 2MASS astrometric positions: 0.017"

More detailed information can be found here

Catalogue parameters

All fields having at least rgi image stacks are delivered with a chi2 images and catalogues centered on the i-band astrometric position. Otherwise, simple one-band ldac catalogues are delivered. The catalogues contain the following Sextractor parameters.

Catalogue parameters and filenames are described in data and parameter description, except for the 'merged ugriz' that contain less information (see the item 'merged catalogue' in the T0004 explanatory table).

Data products and filenames

Terapix products specififc to T0004 stacks available at CADC to CFHTLS registered users are:

Data File Name Type Nb Files
Wide stacks CFHTLS_W_filter_RA-DEC_T0004.fits FITS image 524
Wide weights CFHTLS_W_filter_RA-DEC_T0004_weight.fits FITS image 524
Wide chi2 CFHTLS_W_gri_RA-DEC_T0004.fits FITS image (only stacks with at least gri) 121
Wide chi2 weight CFHTLS_W_gri_RA-DEC_T0004_weight.fits FITS image (only stacks with at least gri) 121
Wide masks CFHTLS_W_RA-DEC_T0004.reg ASCII DS9 compliant in WCS 176
Wide chi2 catalogue CFHTLS_W_filter_RA-DEC_T0004.cat ASCII table (only stacks with at least gri) 421
Wide individual catalogue CFHTLS_W_filter_RA-DEC_T0004.ldac LDAC FITS table 524
Wide merged ugriz catalogue CFHTLS_W_ugriz_RA-DEC_T0004.cat ASCII table (only stacks with at least gri) 121
Deep stacks 25% CFHTLS_D-25_filter_RA-DEC_T0004.fits FITS image 20
Deep weight 25% CFHTLS_D-25_filter_RA-DEC_T0004_weight.fits FITS image 20
Deep chi2 25% CFHTLS_D-25_gri_RA-DEC_T0004.fits FITS image 4
Deep chi2 weight 25% CFHTLS_D-25_gri_RA-DEC_T0004_weight.fits FITS image 4
Deep masks 25% CFHTLS_D_RA-DEC_T0004.reg ASCII DS9 compliant in WCS 4
Deep 25% chi2 catalogue CFHTLS_D-25_filter_RA-DEC_T0004.cat ASCII table 20
Deep 25% individual catalogue CFHTLS_D-25_filter_RA-DEC_T0004.ldac LDAC FITS table 20
Deep 25% merged ugriz catalogue CFHTLS_D-25_ugriz_RA-DEC_T0004.cat ASCII table 4
Deep stacks 85% CFHTLS_D-85_filter_RA-DEC_T0004.fits FITS image 20
Deep weight 85% CFHTLS_D-85_filter_RA-DEC_T0004_weight.fits FITS image 20
Deep chi2 85% CFHTLS_D-85_gri_RA-DEC_T0004.fits FITS image 4
Deep chi2 weight 85% CFHTLS_D-85_gri_RA-DEC_T0004_weight.fits FITS image 4
Deep masks 85% CFHTLS_D_RA-DEC-T0004.reg ASCII DS9 compliant in WCS 4 (same as D-25)
Deep 85% chi2 catalogue CFHTLS_D-85_filter_RA-DEC_T0004.cat ASCII table 20
Deep 85% individual catalogue CFHTLS_D-85_filter_RA-DEC_T0004.ldac LDAC FITS table 20
Deep 85% merged ugriz catalogue CFHTLS_D-85_ugriz_RA-DEC_T0004.cat ASCII table 4

Individual weight map images attached to each CFHT FITS image, their QFITs-in, as well as the QFITS-out quality assessment outputs of each stack are available at CADC.

Important note about the catalogues at CADC

Catalogues with names like 'CFHTLS_D*/W*_z_RA-DEC_T0004.cat' are chisquared catalogues. They are only produced when at least the g,r and i data are available. All catalogues of the kind 'CFHTLS_D*/W*_u,g,r,i,z_RA-DEC_T0004.cat' are extracted with the same chisquared detection image and contain the same objects (i.e., they are all aperture-matched). Columns of catalogs with '.cat' and 'ldac' extentions are defined in the '.param' files. They are listed in the CFHTLS catalogue parameter list. The '.cat' file contains also the E(b-v) in the last column.

Access to T0004 release products (restricted to CFHTLS users):

-  Reminder: CADC is the ONLY access point to CFHTLS release. Please read the data access policy as defined by the CFHT Board of Directors.

-  The Deep+Wide T0004 release at CADC

Annex:

Overview of CFHTLS Data Products.

Articles
article
T0004 explanatory table of Deep+Wide stacks
article
Astrometric and photometric calibration of the terapix T0004 release
How the photometric and astrometric calibration was carried out for the T04 release.
article
The Synoptic T0004 Table
article
T0004 Terapix file naming convention
article
Quick T0004 stack summary table
article
Table of offsets between ZP(CFHT) and ZP(SDSS)

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