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Gal-G8 » History » Version 3

Eli Rykoff, 07/20/2012 01:44 PM

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h1. Gal-G8: Galaxy Detection Fraction vs. CFHTLS Wide
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Galaxy detection fraction at m_i<[20,21,22,23], when referenced to a CFHLS Wide catalog, should have RMS variation <2% when binned into subareas as large as 4x4 degrees.  When further subdivided by photometric redshift, should have RMS<5%.
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The CFHTLS W1 field covers 72 deg^2, half of which should overlap the SV fields.  The mean limiting magnitude in g,r,i,z (MegaCam AB) is [25.47,24.82,24.48,23.60].  The catalogs are 80% complete in g,r,i,z to 24.7,24.0,23.7,22.9].  Absolute astrometric accuracy is ~0.3".  Absolute photometric uncertainty (including systematics) in g,r,i,z is [3%,3%,3%,4%].
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h2. Prerequisites
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* Full depth coadded images over half of CFHTLS W1 (35 deg^2), with SExtractor runs on the detection images.
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* Mangle mask for coadded images
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* Appropriate mask for CFHTLS W1 field.
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* Photometric redshift estimates for SV galaxies. [Should we use our photo-zs or CFHTLS photo-zs?]
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h2. Procedure
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* Apply joint mask to both SV and W1 fields.
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* Match objects from "truth" (W1) to SV catalogs within 1".
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* Bin galaxies in increasing area (0.5x0.5 deg; 1x1; 2x2; 3x3; 4x4)
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* Plot completeness and RMS of SV detections for galaxies between 18<i<[20,21,22,23] for each bin size
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* Plot completeness and RMS of SV detections for galaxies in photoz bins of width 0.2 for galaxies between 18<i<21
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h2. Verdict
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Confirm that detection completeness is consistent across the field.
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h2. Consequences
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If the completeness varies significantly, this could point to problems with the imaging consistency, with the mask, with the coadding pipeline, or with the SEXtractor runs.  We should also be aware of the possibility of residual systematics in the CFHTLS W1 field used as the "truth" table.
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h2. Other Notes
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* The full description of the T0006 processing of CFHTLS is available here: http://terapix.iap.fr/cplt/T0006-doc.pdf