An Off-center Density Peak in the Milky Way's Dark Matter Halo?

TL;DR

This paper investigates the potential offset of the Milky Way's dark matter density peak from its center, revealing a possible several hundred parsec displacement influenced by galactic structures, which impacts dark matter detection signals.

Contribution

It demonstrates that the dark matter density peak can be offset from the galaxy's center by hundreds of parsecs, influenced by the stellar bar, a novel insight into galactic dark matter distribution.

Findings

Offset of 300-400 pc in Eris simulation after z=1

Offset remains below one softening length in dark-matter-only simulations

Offset correlates with stellar bar orientation and affects gamma-ray signals

Abstract

We show that the position of the central dark matter density peak may be expected to differ from the dynamical center of the Galaxy by several hundred parsec. In Eris, a high resolution cosmological hydrodynamics simulation of a realistic Milky-Way-analog disk galaxy, this offset is 300 - 400 pc (~3 gravitational softening lengths) after z=1. In its dissipationless dark-matter-only twin simulation ErisDark, as well as in the Via Lactea II and GHalo simulations, the offset remains below one softening length for most of its evolution. The growth of the DM offset coincides with a flattening of the central DM density profile in Eris inwards of ~1 kpc, and the direction from the dynamical center to the point of maximum DM density is correlated with the orientation of the stellar bar, suggesting a bar-halo interaction as a possible explanation. A dark matter density offset of several hundred parsec greatly affects expectations of the dark matter annihilation signals from the Galactic Center. It may also support a dark matter annihilation interpretation of recent reports by Weniger (2012) and Su & Finkbeiner (2012) of highly significant 130 GeV gamma-ray line emission from a region 1.5 degrees (~200 parsec projected) away from Sgr A* in the Galactic plane.