A map of the outer gas disk of the Galaxy with direct distances from young stars

TL;DR

This paper introduces a new 'pattern matching' method using young star distances to map the Galaxy's gas, achieving higher accuracy than traditional kinematic methods and aiding various astrophysical studies.

Contribution

The paper presents a novel distance estimation technique that improves mapping accuracy of the Galaxy's gas by leveraging young star data instead of relying on kinematic assumptions.

Findings

Pattern matching distances are 24% more accurate than kinematic distances within 15 kpc.

The method shows comparable agreement with parallaxes for masers, with fewer systematic offsets.

The derived gas map enhances understanding of star formation, Galactic structure, and dust mapping.

Abstract

For more than fifty years, astronomers have mapped the neutral hydrogen gas in the Galaxy assuming kinematically derived distances. We employ the distances of nearby young stars, which trace the gas from which they formed, in longitude-latitude-velocity space to map this gas without using kinematic distances. We denote this new method "pattern matching". Analysis of simulated spiral galaxies indicates that our pattern matching distances are 24% more accurate than kinematic distances for gas within 15 kpc of the Sun. The two methods provide similar agreement with parallaxes towards these masers, although the kinematic method shows a small systematic offset in the distance that is not present in the pattern matching distance. Using parallaxes and velocities for masers, we show that this novel method, when matched with nearby Cepheids, performs well compared to kinematics. This analysis is restricted to sources that have a reasonably good match with a member of our Cepheid sample. The distances derived here, and the associated map, have broad utility - from improving our understanding of star formation and the dynamical structure of the Galaxy, to informing 3-D dust maps.