2020ApJ...896...19V

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 star-forming 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 support the basics of a density wave.