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In this work, we derive a spatially resolved map of the line-of-sightvelocity of the interstellar medium and use it, along with a second map ofline-of-sight velocity from Paper I of this series, to determine the nature ofgaseous spiral structure in the Milky Way. This map is derived frommeasurements of the 1.527 $\mu$m diffuse interstellar band (DIB) in stellarspectra from the APOGEE survey and covers the nearest 4-5 kpc of the NorthernGalactic plane. We cross-check this new DIB-based line-of-sight velocity mapwith the map derived in Paper I and find that they agree. We then compare thesemaps with line-of-sight velocity maps derived from simulations ofquasi-stationary density wave spiral structure and dynamic, or material, spiralstructure in a Milky Way-like galaxy. While none of the maps derived from thesesimulations is an exact match to the measured velocity field of the Milky Way,the measurements are more consistent with simulations of dynamic spiralstructure. In the dynamic spiral structure simulation that best matches themeasurements, the Perseus spiral arm is being disrupted.

the astronomical journal

Kinetic Tomography. II. A second method for mapping the velocity field  of the Milky Way Interstellar Medium and a comparison with spiral structure  models