VI. Analysis of the Release Catalogs

1. Comparison of Achieved Performance of the All-Sky Release Catalogs
with Level 1 Science Specification

n. Galactic Plane Performance

The 2MASS Survey has no Level 1 Specifications in the Galactic Plane with regard to completeness, reliability, and photometric accuracy. This document contrasts the achieved performance of the Point Source Catalog in the Galactic Plane with the Level 1 Specifications appropriate for high galactic latitudes. It is found that the effects of confusion noise on the properties of the Point Source Catalog are most noticeable in regions (a) within ~ ±7° of the Galactic Center and ~ ±3° of the Galactic Plane, and (b) within a ~ 6° radius of the Galactic Center.

The nominal specifications of the 2MASS Point Source Catalog apply to high galactic latitudes and not the Galactic Plane, where the performance of the 2MASS data reduction pipeline is limited by confusion noise. Since approximately 60% of the sources in the 2MASS Point Source Catalog have galactic latitudes of |b| < 10°, it is essential characterize the point source properties in the Galactic Plane. This summarizes the properties of Point Sources in the Galactic Plane.

A simple, yet powerful, visual representation of the results can be obtained by reviewing the "GIF movies" (Figures 1--6), which show images of the differential star counts in 0.2-mag bins presented in the Galactic Aitoff projection. Click on the figure thumbnails to view the "movie."

GIF Movies of the 2MASS Sky
BandLow StretchHigh stretch
 Figure 1Figure 4
 Figure 2Figure 5
 Figure 3Figure 6

The salient results of a detailed analysis of these movies and other images are as follows:

  1. Completeness
    The primary area of incompleteness relative to the nominal 2MASS limits Level occurs within (a) a few degrees of the Galactic Plane at ± 75° from the Galactic Center, and (b) with ~ 5° from the Galactic Center.
  2. Colors toward the Galactic Center
    Systematic color biases in the near-infrared colors are present at the scale of individual coadds. The RMS of these colors deviations are 0.022 mag in H-Ks, and can be partially explained by a point spread function grid that did not sample finely enough the range of seeing conditions present in the Survey. These color biases are likely present in the entire Survey, but are only clearly observed in the Galactic Center, where there are a large number stars in individual Atlas Images.
  3. Astrometry
    The quoted astrometric uncertainties in the 2MASS Point Source Catalog are systematically larger in the Galactic Plane for the region between approximately 60° of the Galactic Center and 1° of the Galactic Plane. The typical major and minor axis astrometric uncertainty in this region is ~ 0.075´´-0.80´´ each axis.
  4. Magnitude limits at SNR=10
    Within approximately a 6° radius of the Galactic Center, the average magnitude for a SNR=10 source is up to ~2 mag brighter than the typical SNR=10 source in unconfused regions. A similar, but less dramatic, trend is observed within 1°-3° of the Galactic Plane and ~ 60° of the Galactic Center.

[Last Updated: 2003 March 31; by J. Carpenter]

Return to VI.1.