Interstellar Gas and a Dark Disk

TL;DR

This paper proposes a method to detect or constrain a thin dark matter disk in the Milky Way using interstellar gas properties, but current data uncertainties limit definitive conclusions.

Contribution

It introduces a novel approach linking gas scale heights to dark disk presence and discusses current data limitations affecting constraints.

Findings

Current data are inconsistent and limit constraints.

Uncertainty in gas parameters dominates the bounds.

Potential evidence for a dark disk depends on gas measurements.

Abstract

We introduce a potentially powerful method for constraining or discovering a thin dark matter disk in the Milky Way. The method relies on the relationship between the midplane densities and scale heights of interstellar gas being determined by the gravitational potential, which is sensitive to the presence of a dark disk. We show how to use the interstellar gas parameters to set a bound on a dark disk and discuss the constraints suggested by the current data. However, current measurements for these parameters are discordant, with the uncertainty in the constraint being dominated by the molecular hydrogen midplane density measurement, as well as by the atomic hydrogen velocity dispersion measurement. Magnetic fields and cosmic ray pressure, which are expected to play a role, are uncertain as well. The current models and data are inadequate to determine the disk's existence, but, taken at face value, may favor its existence depending on the gas parameters used.