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

TL;DR

This study uses 2MASS star counts and a galactic model to precisely estimate key parameters of the Milky Way's thin disk, thick disk, and spheroid across the entire sky, including the plane.

Contribution

It provides the first comprehensive parameter estimation of the Galaxy's structure using all-sky star counts with HEALPix grid comparison.

Findings

Thin disk scale length: 2120 ± 200 pc

Thick disk scale height: 640 ± 70 pc

Spheroid central dimension: 400 ± 100 pc

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.