3pi DVO Database Release 2012.06.06

(Up to the IPP for PS1)

The following tables and images explore the number of real and false detections in the 3pi database released 2012.06.06 as a function of filter, magnitude, and position on the sky. Note that this database contains data up through 2012.01.21 and is based entirely on the nightly science analysis. The photometric zero point has been set by ubercal + relative photometry, and the astrometric terms are set locally by relative astrometry, with a tie down of the 2MASS data. The database contains, in addition to the GPC1 data, data from 2MASS (JHK + synthetic grizy), WISE, and SuperCosmos?. The analysis below relates to only the GPC1 detections, except for the count of objects, which may count a small number of objects with only 2MASS-based synthetic photometry from the region DEC = -35 to -30.

The table below lists the total number of GPC1 detections in each filter (all detections) as well as the number of GPC1 detections per filter associated with objects with more than 2 measurements (highly likely to be a real astrophysical object). Below are images showing the distribution of these values on the sky. The mean false fraction is the value (Nall - Ngood) / Ngood, while the median false fraction is the median of the per-pixel values (1 pixel is 10 arcmin x 10 arcmin).

filter good detections all detections mean false frac median false fraction
g 3.761962e+09 4.589117e+09 0.180 0.491
r 4.865315e+09 5.539615e+09 0.122 0.277
i 6.311162e+09 7.113843e+09 0.113 0.240
z 6.767039e+09 7.558130e+09 0.105 0.219
y 4.889023e+09 5.473861e+09 0.107 0.265

Some totals:

  • Nall detections = 3.27e+10
  • Ngood detections = 2.66e+10
  • mean false fraction = 13.8%
  • Nall objects = 2.23e+09
  • Ngood objects = 1.49e+09
  • Nfalse objects = 7.4e+08
  • mean false objects = 49.7%

(Note that these total counts of objects includes some objects from the region Dec = -35 to -30, where there is little GPC1 data. In this region, objects with synthetic grizy photometry based on 2MASS are included in the totals, but only amount to a small contamination).

Object and Detection Counts across the 3pi region

The following images show the density of objects (not detections) as distributed across the sky, with i band magnitude limits as from 16.0 to 23.5 (as given in the left-hand column).

i mag limit log(objects per square degree) (dark : 2.0, light: 6.0)
16.0
16.5
17.0
17.5
18.0
18.5
19.0
19.5
20.0
20.5
21.0
21.5
22.0
22.5
23.0
23.5

The following images show the logarithm (base 10) of the density of 'good' GPC1 detections as distributed across the sky for each of the five filters grizy.

filter log(good measurements per square degree) (dark : 2.5, light : 7.0)
g
r
i
z
y

The following images show the logarithm (base 10) of the density of all GPC1 detections as distributed across the sky for each of the five filters grizy.

filter log(good measurements per square degree) (dark : 2.5, light : 7.0)
g
r
i
z
y

The following images show the false positive fraction [(Nall - Ngood) / Ngood] as a function of position.

filter false fraction (dark : -0.02, light : 1.02)
g
r
i
z
y

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