Kcor magnitudes
2MASS gives reliable isophotal magnitudes K20 - comparable depth to 2dF for most galaxies.
can easily determine average surface brightness within this isophote ľK20.
2MASS gives total magnitude Ktot - noisy but OK at high latitude
can use K20 , ľK20 + simple model to estimate total magnitude, compare with Ktot
Kcor = K20 - min(1.5 e(1.25(ľK20 -20)) , 0.5)
Robust to confusion noise
Statistical error ~ 0.11m
Overall systematic error << 0.1m
Possible biases at 0.05m level vs galaxy profile
No extinction correction to the correction!