Galactic Parameters from Whole Sky 2MASS Star Counts

The whole sky differential star counts (DSC) with 1 degree resolution are retrieved from 2MASS online data service. Galaxy with double exponential thin and thick disks and a single power law luminosity function (LF) is used to interpret the 2MASS data. The slope of the DSC appears roughly isotropic over the whole sky, the average value is ∼ 0.32, which corresponds to a power law index ∼ 1.8 of the LF. We find that the scale-length and scale-height the thin disk are ∼ 3.0 kpc and ∼ 245 pc, and those of the thick disk are ∼ 3.0 kpc and ∼ 780 pc. The ratio of the thick disk to the thin disk is ∼ 7%. The location of Sun above the disk is ∼ 15 pc. A comparison of the data and model and their discrepancy are also provided.