A New Multi-Tracer Approach to Defining the Spiral arm width in the Milky Way

TL;DR

This study introduces a multi-tracer method to measure the Milky Way's spiral arm width, revealing a consistent separation between star-forming regions and older gas that supports density wave theory.

Contribution

It presents a novel approach using multiple tracers to quantify spiral arm width and its variation with galactic radius, providing new observational evidence.

Findings

Typical separation of 250 +/- 50 pc between tracers

Separation increases by about 25 +/- 5 pc per kpc with radius

Results support the density wave theory of spiral structure

Abstract

We analyze recent observations of the spiral arm width in the Milky Way, as a function of the galactic radius, and we compare this relation with the prediction from the density wave theory. We use the following method: in each spiral arm, we concentrate on the separation (or offset) between the starforming region (radio masers) near the shock front of a density wave, and the aged star region (diffuse CO gas) near the potential minimum of a density wave; we take this separation between these two tracers as the arm width. New results: we find a typical separation (maser to diffuse CO gas) near 250 +/- 50 pc, and an increase of this separation with galactic radius of about 25 +/- 5 pc per kpc. We note that, as expected, this separation is somewhat smaller than that found earlier between the dust lane and the aged star region. Overall, these results supports the basics of a density wave.