Local Spiral Structure Traced by Red Clump Stars

TL;DR

This study uses Gaia and 2MASS data to map the nearby spiral structure of the Milky Way with old stars, revealing an arm segment near the Sun and differences from young star tracings.

Contribution

It presents the first detailed mapping of the Galaxy's spiral arms using old red clump stars, highlighting structural differences from young star tracings.

Findings

Identified an arc-like spiral feature passing near the Sun.

Found significant offsets between old and young star tracings of spiral arms.

Discovered that the spiral arm traced by old stars has a larger pitch angle.

Abstract

Using the cross-matched data of Gaia EDR3 and the 2MASS Point Source Catalog, a sample of RC stars with parallax accuracies better than 20% is identified and used to reveal the nearby spiral pattern traced by old stars. As shown in the overdensity distribution of RC stars, there is an arc-like feature extended from $l~\sim$ 90$^\circ$ to $\sim$ 243$^\circ$, which passed close to the Sun. This feature is probably an arm segment traced by old stars, indicating the Galaxy potential in the vicinity of the Sun. By comparing to the spiral arms depicted by young objects, we found that there are considerable offsets between the two different components of Galactic spiral arms. The spiral arm traced by RC stars tends to have a larger pitch angle, hence a more loose wound pattern.