T. Jarrett, IPAC
(980417)
Several nights of 2MASS data have been specifically designated as RTB data sets (to be used to debug and check different versions of the 2MAPPS pipeline reduction).
The extended source results (GALWORKS output) for 971110n has been fully analyzed to gauge the performance of GALWORKS on a much larger scale than previously attempted. The plots and tables given below summarize the results. For a summary of other RTB nights, see Summary of GALWORKS Results for RTB 971205n -- low source density fields -- .
The 971110n data set includes 40 full 6 degree science scans. Most of the scans, 32 in total, are from low stellar source density fields (< 10**3.2 stars/deg^2, K < 14), with the remaining 8 scans located in mid-to high source density fields (between 3.7 and 4.0 log stars/deg^2, K < 14). Results for the high density scans can be found in Summary of GALWORKS Results for RTBs 971110n & 971205n -- high source density fields -- .
Only the scans subject to low stellar source density are discussed here.
Each source deemed "extended" by GALWORKS was carefully examined by 'eye' using tools developed by Jarrett. Nearly 1600 sources were part of the 971110n extended source output (from low density scans), including part of the Abell 262 region. Each source was 'classified' by viewing the J,H and K postage stamp images, as well as the corresponding DSS (optical) stamp images and the '3-color' image generated from the JH&K images (the latter is quite powerful since it helps the user see "color" as well as increase the snr for the low surface brightness "fuzz" around galaxies). Sources were classified into the following catagories:
GALWORKS is 'tuned' to optimize galaxy completeness at the
expense of reliability. The minimum acceptible reliability
chosen to optimize completeness is about 80%. That is to say,
we tolerate a 20% contamination of false galaxies
to our extended source database in order to be >95% complete
in galaxy detection/extraction. However, in order to meet
the level-1 specification for catalog generation
(reliab > 98%)
we will apply various methods to weed out the false sources
(which, as will be shown below, are double stars and artifacts,
like meteor streaks). These methods will be applied in
a 'post-processing" phase; they include application of
decision trees,
Star - Galaxy Discrimination Parameters
Notes:
galaxies == filled white circles
stars == small red triangles
doubles == large red triangles
triples == blue crosses
artifacts == red crosses
unknowns == yellow dots
Extended Source Colors
Notes: colors computed using fixed circular radius=7" apertures; galaxies are denoted by the white filled circles; double stars by the red triangles; mean colors are represented K-corrections for spirals are represented by the magenta line and triangle points -- each point is 0.1 in redshift -- and ellipticals by the grey line and square points; the main sequence (dwarf and giant branches) are shown in green.
Yellow dotted lines represent "redshift" zones; they are roughly parallel to the "giant" star branch, and roughly perpendicular to the K-correction track.
The blue dashed line represents a color-color criterion (color break) between galaxies and false sources (double stars mostly). TChester has investigated this line in more depth by looking at the point sources in the database. See Distinguishing Galaxies from Point Sources Using Point Source Color-Color Plots .
