[KIDS] update on completeness/contamination

[Francesco La Barbera]

Dear All,

here it's some updates about completeness/contamination estimates in the
CFHT overlap area, based
on the matched catalog produced by  Mario.

The first attached plot is an updated version of what we have sent
yesterday, but now we also plot the fraction
of spurious sources, i.e. contamination, as a function (KIDSCAT) MAG_AUTO
in the bottom panel
of the same figure.
The fraction of "candidate spurious" is defined as the ratio
#OBJECTS_NOT_MATCHED_WITH_CFHT/#OBJECTS_MATCHED

The difference between the black adn red curve (bottom panel) is that for
the red curve I selected only KIDSCAT detections
with SEX_FLAG==0|SEXFLAG>=16, hence removing sources blended with other
objects.
As you can see most of "candidate spurious" sources at bright mags (they
are not spurious, indeed, see below)  have been
deblended by S-Ex.

The second attached plot shows the spatial distribution of spurious
sources, black and red colors have the same meaning as
above. There are clearly some spurious features (e.g. detections along a
residual satellite track),
but in most cases (pls, compare black vs. red dots), the "candidate
spurious" objects are actually deblended sources.

The third attached plot shows the spatial distribution of "candidate
spurious" (black circles) in a region around a bright star
(pixel coordinates x~25000, y~10000). Most of the objects are true
sources!! and they are actually missing in the
CFHT catalog (maybe, they were just masked out by the CFHT masks).

Another example is the last attached file, contamination_2.jpg, where you
can clearly see "true spurious" objects
along a residual satellite track. Other "spurious" are just S-Ex blends.

To summarize:
1) completeness estimates within KIDSCAT seem to work OK, at least for this
field where we have an external comparison;
2) for what concerns the objects present only in the KIDS image (not in the
CFHT one), i.e. the possible spurious, we have the following cases:
  A) most of them are *true* sources, close to brighter companions, likely
detected only in KIDS because of the better seeing wrt CFHT;
  B) some of these "true" sources are not present  in the CFHT catalog as
they were  probalby masked out, for some reason, in CFHT;
  C) finally, we have "true" contaminants, mostly associated to satellite
tracks, still present in the KIDS image.
3) as a result, the red curve in bottom panel of
Fig.~CFHT_KIDS_COMPLETENESS_CONTAMINATION_135_-1.5_r.jpg gives
an **upper** estimate of contamination in this r-band image. Contamination
is <~2% at bright mags (<23), increasing to at most
10% at faint mags (~24.5-25).

Now, Nicola is producing catalogs for different values of DETECTION_MINAREA
and THRESHOLD. Mario will match them again,  and then we can test
how contamination/completeness change as a function of detection parameters.

Cheers,
Francesco
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