| 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 only | griz only | all ugriz | all gri (=chi2) | Total u/g/r/i/ or z |
| W1 | 24 | 1 | 19 | 44 | 73 |
| W2 | 19 | 1 | 0 | 20 | 38 |
| W3 | 28 | 8 | 5 | 41 | 49 |
| W4 | 4 | 1 | 11 | 16 | 16 |
| Total | 75 | 11 | 35 | 121 | 176 |
| W1-ugriz | W2-ugriz | W3-ugriz | W4-ugriz |
| 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.
