Disc-Based Estimation of the Local Dark Matter Density and Velocity Distribution in IllustrisTNG50

Abstract: We study the dark matter (DM) density and velocity distribution in the solar neighborhood of Milky Way-like galaxies using the TNG50-1 run of the IllustrisTNG simulation suite. Milky Way-like galaxies are selected according to both their halo mass and their bulge-to-total stellar mass ratio, and the solar-neighborhood region within each galaxy is identified from the positions and number density of stars, so that DM particles associated with the galactic disc are extracted while contributions from the halo component are suppressed. Averaging over the selected galaxies, we obtain a local DM density of $ρ\simeq 0.47\pm0.02~{\rm GeV\,cm<sup>{-3}}$, consistent with the range inferred from observations. The disc-based extraction gives a higher peak density, $0.41\pm0.02~{\rm GeV\,cm<sup>{-3}}$, than the value $0.34\pm0.02~{\rm GeV\,cm<sup>{-3}}$ from a simple distance-based extraction, probably because it excludes the low-density DM in the halo. The width of the density distribution, on the other hand, is nearly unchanged. The velocity distribution is well described by an isotropic Maxwellian with a peak velocity of about $226~{\rm km~s<sup>{-1}}$, close to the value assumed in the standard halo model. The differences in the density and velocity distributions between our disc-based and simple distance-based extractions are not so large as to significantly affect the interpretation of direct-detection experiments.