Estimating the local dark matter density in a non-axisymmetric wobbling disc

Abstract

The density of dark matter near the Sun is important for experiments hunting for dark matter particles in the laboratory, and for constraining the local shape of the Milky Way's dark matter halo. Estimates to date have typically assumed that the Milky Way's stellar disc is axisymmetric and in a steady-state. Yet the Milky Way disc is neither, exhibiting prominent spiral arms and a bar, and vertical and radial oscillations. We assess the impact of these assumptions on determinations of the local dark matter density by applying a free-form, steady-state, Jeans method to two different N-body simulations of Milky Way-like galaxies. In one, the galaxy has experienced an ancient major merger, similar to the hypothesized Gaia-Sausage-Enceladus; in the other, the galaxy is perturbed more recently by the repeated passage and slow merger of a Sagittarius-like dwarf galaxy. We assess the impact of each of the terms in the Jeans-Poisson equations on our ability to correctly extract the local dark matter density from the simulated data. We find that common approximations employed in the literature - axisymmetry and a locally flat rotation curve - can lead to significant systematic errors of up to a factor ~1.5 in the recovered surface mass density ~2kpc above the disc plane, implying a fractional error on the local dark matter density of order unity. However, once we add in the tilt term and the rotation curve term in our models, we obtain an unbiased estimate, consistent with the true value within our 95% confidence intervals for realistic 20% uncertainties on the baryonic surface density of the disc. Other terms - the axial tilt, 2:nd Poisson and time dependent terms - contribute less than 10% to the local dark matter density (given current data) and can be safely neglected for now. In the future, as more data become available, these terms will need to be included in the analysis.

15 pages, 16 figues. Submitted to MNRAS. Comments welcome!

References in corpus (18)

• Are the Magellanic Clouds on their First Passage about the Milky Way?
• The Local Dark Matter Density
• On the mass-to-light ratio of the local Galactic disc and the optical luminosity of the Galaxy
• The observed spiral structure of the Milky Way
• A new determination of the local dark matter density from the kinematics of K dwarfs
• Is the Milky Way ringing? The hunt for high velocity streams
• The Complex Structure of Stars in the Outer Galactic Disk as revealed by Pan-STARRS1
• Handling the Uncertainties in the Galactic Dark Matter Distribution for Particle Dark Matter Searches
• The Rotation Curve, Mass Distribution and Dark Matter Content of the Milky Way from Classical Cepheids
• The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc
• A centrally heated dark halo for our Galaxy
• Measuring the local dark matter density with LAMOST DR5 and Gaia DR2
• Tracing the Galactic spiral structure with embedded clusters
• Galactoseismology and the Local Density of Dark Matter
• The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia
• Implications of a time-varying Galactic potential for determinations of the dynamical surface density
• Exploring the pertubed Milky Way disk and the substructures of the outer disk
• Gaia-DR2 extended kinematical maps. Part II: Dynamics in the Galactic disk explaining radial and vertical velocities

Cited by in corpus (10)

• Self-consistent models of our Galaxy
• Axion Couplings in Grand Unified Theories
• Jupiter missions as probes of dark matter
• Weighing the Galactic disk using phase-space spirals III. Probing distant regions of the disk using the Gaia EDR3 proper motion sample
• Mapping Dark Matter in the Milky Way using Normalizing Flows and Gaia DR3
• European Spallation Source as a searching tool for an ultralight scalar field
• Excluding Primordial Black Holes as Dark Matter Based on Solar System Ephemeris
• Sliding into DM: Determining the local dark matter density and speed distribution using only the local circular speed of the Galaxy
• Local dark matter density from Gaia DR3 K-dwarfs using Gaussian processes
• Neutrino Lorentz invariance violation from the CPT-even SME coefficients through a tensor interaction with cosmological scalar fields