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 NIR intensity peaks). Note that the FIRST survey is restricted to Declinations between -10 and 60 degrees.

a. Statistics

About 23,000 matches between 2MASS and FIRST with a search radius of 5" give the following:

RA: Ave = 0.02", rms = 0.85", Median = 0.04" (FIRST-2MASS)
Dec: Ave = 0.03", rms = 0.87", Median = 0.03" (FIRST-2MASS)

b. Plots

• 2MASS vs. FIRST positions plotted along the Dec axis

• 2MASS vs. FIRST Positions: dRA vs. dDec

• 2MASS vs. FIRST Positions Histogram

[Last Updated: 2002 Aug 4; by Tom Jarrett]