The z Distribution of Hydrogen Clouds and Masers with Kinematic Distances

TL;DR

This study analyzes the vertical distribution of hydrogen clouds and masers in the Milky Way to estimate the Sun's position relative to the Galactic plane and the disk's scale height, excluding Local-arm objects for accuracy.

Contribution

It provides new estimates of the Sun's height and the disk scale height using kinematic distances and a self-gravitating isothermal disk model, excluding Local-arm influences.

Findings

Estimated Sun's height from the Galactic plane (~ -6 to -10 pc)

Derived disk scale heights (~24 to 28 pc) for different object types

Excluded Local-arm objects to improve distribution symmetry

Abstract

Data on HII regions, molecular clouds, and methanol masers have been used to estimate the Sun's distance from the symmetry plane zo and the vertical disk scale height h. Kinematic distance estimates are available for all objects in these samples. The Local-arm (Orion-arm) objects are shown to affect noticeably the pattern of the z distribution. The deviations from the distribution symmetry are particularly pronounced for the sample of masers with measured trigonometric parallaxes, where the fraction of Local-arm masers is large. The situation with the sample of HII regions in the solar neighborhood is similar. We have concluded that it is better to exclude the Local arm from consideration. Based on the model of a self-gravitating isothermal disk, we have obtained the following estimates from objects located in the inner region of the Galaxy (R<= Ro): zo= -5.7+/-0.5 pc and h2=24.1+/-0.9 pc from the sample of 639 methanol masers, zo=-7.6+/-0.4 pc and h2=28.6+/-0.5 pc from 878 HII regions, zo=-10.1+/-0.5 pc and h2=28.2+/-0.6 pc from 538 giant molecular clouds.