Galactic Parameters from Whole Sky 2MASS Star Count

TL;DR

This study analyzes whole sky star counts from 2MASS data using a galactic model with thin and thick disks, deriving structural parameters and luminosity function characteristics.

Contribution

It provides new estimates of galactic disk scale parameters and the luminosity function index based on comprehensive 2MASS star count data.

Findings

Thin disk scale-length ~3.0 kpc

Thick disk scale-height ~780 pc

Thick-to-thin disk ratio ~7%

Abstract

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.