Local spiral structure based on the Gaia EDR3 parallaxes

TL;DR

This study uses Gaia EDR3 parallaxes of young OB stars to map the Milky Way's local spiral structure in detail, revealing inhomogeneities and extending previous maser-based models.

Contribution

It provides the most detailed local spiral structure map using spectroscopically confirmed OB stars, extending and refining maser-based models.

Findings

Clear delineation of local spiral arms within 5 kpc of the Sun.

Extension and densification of spiral structure beyond maser data.

Evidence of inhomogeneity in the Galaxy's spiral pattern.

Abstract

Context. The astrometric satellite Gaia is expected to significantly increase our knowledge as to the properties of the Milky Way. The Gaia Early Data Release 3 (Gaia EDR3) provides the most precise parallaxes for many OB stars, which can be used to delineate the Galactic spiral structure. Aims. We investigate the local spiral structure with the largest sample of spectroscopically confirmed young OB stars available to date, and we compare it with what was traced by the parallax measurements of masers. Methods. A sample consisting of three different groups of massive young stars, including O-B2 stars, O-B0 stars and O-type stars with parallax accuracies better than 10% was compiled and used in our analysis. Results. The local spiral structures in all four Galactic quadrants within $\approx$5 kpc of the Sun are clearly delineated in detail. The revealed Galactic spiral pattern outlines a clear sketch of nearby spiral arms, especially in the third and fourth quadrants where the maser parallax data are still absent. These O-type stars densify and extend the spiral structure constructed by using the Very Long Baseline Interferometry (VLBI) maser data alone. The clumped distribution of O-type stars also indicates that the Galaxy spiral structure is inhomogeneous.