II. User's Guide to the 2MASS All-Sky Data Release

3. Extended Source Catalog (XSC)

d. General Properties

v. 2MASS XSC vs. VLA FIRST Astrometry

We compare the equatorial coordinate positions of the 2MASS XSC standard positions (based on J-band peak) and the VLA FIRST radio sources. Since both surveys should have excellent astrometry, we restrict the comparison to those sources within a 5´´ search radius (which also minimizes the astrophysical differences between radio and near-infrared intensity peaks). Note that the FIRST survey is restricted to declinations between -10° and +60°.

Statistics

About 23,000 matches between 2MASS and FIRST, found using a search radius of 5´´, result in the following statistics:

Astrometric Comparison (=FIRST-2MASS)

	Average	RMS	Median
RA	0.02´´	0.85´´	0.04´´
Dec	0.03´´	0.87´´	0.03´´

Diagrams

In Figure 1 we show the 2MASS/ FIRST positional comparison as a function of declination. In Figure 2 we show the global comparison in both right ascension and declination. In Figure 3 we show a histogram of the 2MASS vs. FIRST positional comparison.

Figure 1	Figure 2	Figure 3

[Last Updated: 2002 Aug 4; by T. Jarrett]