Galactic kinematics with RAVE data: I. The distribution of stars towards the Galactic poles

TL;DR

This study uses RAVE and other data to analyze the vertical distribution and kinematics of G and K stars towards the Galactic poles, identifying structural components and their properties.

Contribution

It provides new measurements of scale heights for the thin and thick disks and insights into their formation mechanisms based on kinematic discontinuities.

Findings

Thin disk scale height: 225±10 pc

Thick disk scale height: 1048±36 pc

Kinematic gap suggests non-continuous thick disk formation

Abstract

We analyze the distribution of G and K type stars towards the Galactic poles using RAVE and ELODIE radial velocities, 2MASS photometric star counts, and UCAC2 proper motions. The combination of photometric and 3D kinematic data allows us to disentangle and describe the vertical distribution of dwarfs, sub-giants and giants and their kinematics. We identify discontinuities within the kinematics and magnitude counts that separate the thin disk, thick disk and a hotter component. The respective scale heights of the thin disk and thick disk are 225$\pm$10 pc and 1048$\pm$36 pc. We also constrain the luminosity function and the kinematic distribution function. The existence of a kinematic gap between the thin and thick disks is incompatible with the thick disk having formed from the thin disk by a continuous process, such as scattering of stars by spiral arms or molecular clouds. Other mechanisms of formation of the thick disk such as `created on the spot' or smoothly `accreted' remain compatible with our findings.