A Galaxy Model from 2MASS Star Counts in the Whole Sky Including the Plane

Abstract

We use the star counts model of Ortiz & L\'epine (1993) to perform an unprecedented exploration of the most important galactic parameters comparing the predicted counts with the 2MASS observed star counts in the J, H and K_S bands for a grid of positions covering the whole sky. The comparison is made using a grid of lines-of-sight given by the HEALPix pixelization scheme. The resulting best fit values for the parameters are: (2120 +- 200) pc for the radial scale length and (205 +- 40) pc for the scale height of the thin disk, with a central hole of (2070_{-800}^{+2000}) pc for the same disk; (3050 +- 500) pc for the radial scale length and (640 +- 70) pc for the scale height of the thick disk; (400 +- 100) pc for the central dimension of the spheroid, (0.0082 +- 0.0030) for the spheroid to disk density ratio, and (0.57 +- 0.05) for the oblate spheroid parameter.