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Gal-G9: False Galaxy Contaminants vs. CFHTLS Wide

In a masked coadd catalog, the ratio of false galaxy contaminants, such as satellite trails, to real galaxies should be <2% in any 0.05x0.05 degree square field. [R--28 is that ratio be "known to 1%." R--30 is that fluctuations in the final catalog must be smaller than 2% rms over scales from 0.05 to 4 degrees.]

As with test Gal-G8, we will use the CFHTLS W1 field as a "truth" testing catalog. See Gal-G8 for details on CFHTLS W1.

Questions:

  • What magnitude range do we want to look at here? We need to stay within reasonable completeness limits.
  • How do we disentangle false galaxies due to satellite trails and such with false galaxies due to star/galaxy separation problems? The S/G requirements are much stricter.

Prerequisites

  • The prerequisites are very similar to what's needed for Gal-G8.
  • Full depth coadded images over half of CFHTLS W1 (35 deg^2), with SExtractor runs on the detection images.
  • Mangle mask for coadded images
  • Appropriate mask for CFHTLS W1 field.

Procedure

  • Apply joint mask to both SV and W1 fields.
  • Match objects from "truth" (W1) to SV catalogs within 1".
  • Bin galaxies in increasing area (0.05x0.05 deg to 4x4 deg)
  • Plot false galaxy rate and RMS when compared to CFHTLS W1 for galaxies between 18<i<22 (?).

Verdict

Confirm that false galaxy rate is small and consistent across the field.

Consequences

If the false galaxy rate varies significantly, this could point to problems with the imaging consistency, with the mask, with the coadding pipeline, with the SEXtractor runs, or with star/galaxy separation. 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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