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Wide field
External rms errors with respect to SDSS-DR8
σ u ∗ σ g σ r σ i σ z
rms [mag.] rms [mag.] rms [mag.] rms [mag.] rms [mag.]
W1 0.016 0.008 0.009 0.006 0.010
W2 0.011 0.005 0.004 0.005 0.012
W3 0.009 0.005 0.005 0.004 0.005
W4 0.009 0.003 0.007 0.006 0.005
Table 12: External rms errors of the CFHTLS T0007 u ∗ , g, r, i and z-band Wide surveys. They are derived
from the variance of the magnitude offset distributions between the SDSS-DR8 and CFHTLS-T0007, in the W1,
W2, W3 and W4 fields. The error estimates only use 115/171 Wide fields. In contrast with the internal errors,
most common source loci are outside the noisy overlapping regions, and the selected stellar sources used for the
comparison are brighter.
4.4.4 External photometric errors
The external photometric errors are derived from the rms of the mean CFHTLS-SDSS magnitude offset
values, δ m=u ∗ ,g,r,i/y,z, in each Wide field separately. They are measured by adding the 115 offsets to
CFHTLS-SDSS common sources of each relevant tile and then by computing the rms of the CFHTLS-
SDSS residual over the tile.
The external errors are quoted for each Wide in Table 12. As expected the g, r and i-bands are on
the average better than the u ∗ and z. W1 seems slightly worse than W2, W3 and W4, probably due
to contamination by several outliers reported in the previous section. The overall external field to field
calibration is around 1.5% in u ∗ and z, and below 1.0% in g, r and i/y.
4.4.5 CFHTLS Wide photometric precision
To summarize, the systematic photometric precision in the CFHTLS Wide T0007 calibration (or field to
field scatter) can be measured using :
• the dispersion of the tile magnitude offsets with SDSS (section 4.4.4 and table 12)
• the dispersion of the the magnitude offsets between adjacent fields measured in the overlapping
regions (section 4.4.2 and table 9)
These two measurements are in good agreement and show field to field scatters of :
• 1.5% in u∗ and z bands
• 1% in g, r and i/y bands
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