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

TL;DR

This paper introduces a second method for mapping the Milky Way's interstellar medium velocity field using diffuse interstellar bands, compares it with previous maps, and finds it aligns more with dynamic spiral structure models.

Contribution

It presents a new DIB-based velocity map of the Milky Way and compares it with existing models, favoring dynamic spiral structure interpretations.

Findings

The new DIB-based velocity map agrees with previous measurements.

Measurements are more consistent with dynamic spiral structure models.

The Perseus arm appears to be disrupted in the best-matching simulation.

Abstract

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