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 ~ ±75 degrees of the Galactic Center
and ~ ±3 degrees of the Galactic Plane, and (b) within
a ~ 6 degree 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 deg, it is essential characterize the point source properties in the Galactic Plane. This document 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 listed in the table below which show images of the differential star counts in 0.2 magnitude bins presented in the Galactic Aitoff projection.
| Band | Low Stretch | High stretch |
|---|---|---|
| J | X | X |
| H | X | X |
| Ks | X | X |
The salient results of a detailed analysis of these movies and other images are as follows:
The primary area of incompleteness relative to the nominal 2MASS limits Level occurs within (a) a few degrees of the Galactic Plane at ± 75 degrees from the Galactic Center, and (b) with ~ 5 deg from 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 coadds.
The quoted astrometric uncertainties in the 2MASS Point Source Catalog are systematically larger in the Galactic Plane for the region between apprximately 60 degrees of the Galactic Center and 1 degree of the Galactic Plane. The typical major and minor axis astrometric uncertainty in this region is ~ 0.075-0.80 arceconds for each axis.
Within approximately a 6 degree radius of the Galactic Center, the average magnitude for a SNR=10 source is up to ~2 magnitudes brighter than the typical SNR=10 source in unconfused regions. A similar, but less dramatic, trend is observed within 1-3 degrees of the Galactic Plane and ~ 60 degrees of the Galactic Center,
[Last Updated: 2003 March 31; by J. Carpenter]
