Galactic spiral structure revealed by Gaia EDR3

TL;DR

This study uses Gaia EDR3 data to map the Milky Way's spiral arms by analyzing the distribution of young stars, open clusters, and Cepheids, revealing new details about the spiral structure and arm geometry.

Contribution

It provides the first detailed density maps of spiral arms using Gaia EDR3 data, highlighting differences from previous models and extending the known length of the Local Arm.

Findings

Spiral arm segments are traced by overdensities of young stars and clusters.

The geometry of the spiral arms, especially in the III quadrant, differs from previous models.

The Local Arm extends at least 8 kpc, longer than previously thought.

Abstract

Using the astrometry and integrated photometry from the Gaia Early Data Release 3 (EDR3), we map the density variations in the distribution of young Upper Main Sequence (UMS) stars, open clusters and classical Cepheids in the Galactic disk within several kiloparsecs of the Sun. Maps of relative over/under-dense regions for UMS stars in the Galactic disk are derived, using both bivariate kernel density estimators and wavelet transformations. The resulting overdensity maps exhibit large-scale arches, that extend in a clumpy but coherent way over the entire sampled volume, indicating the location of the spiral arms segments in the vicinity of the Sun. Peaks in the UMS overdensity are well-matched by the distribution of young and intrinsically bright open clusters. By applying a wavelet transformation to a sample of classical Cepheids, we find that their overdensities possibly extend the spiral arm segments on a larger scale (~10 kpc from the Sun). While the resulting map based on the UMS sample is generally consistent with previous models of the Sagittarius-Carina spiral arm, the geometry of the arms in the III quadrant (galactic longitudes $180^\circ < l < 270^\circ$) differs significantly from many previous models. In particular we find that our maps favour a larger pitch angle for the Perseus arm, and that the Local Arm extends into the III quadrant at least 4 kpc past the Sun's position, giving it a total length of at least 8 kpc.