The highest-speed local dark matter particles come from the Large Magellanic Cloud (1909.04140v1)

Abstract: Using N-body simulations of the Large Magellanic Cloud (LMC's) passage through the Milky Way (MW), tailored to reproduce observed kinematic properties of both galaxies, we show that the high-speed tail of the Solar Neighborhood dark matter distribution is overwhelmingly of LMC origin. Two populations contribute at high speeds: 1) Particles that were once bound to the LMC, and 2) MW halo particles that have been accelerated owing to the response of the halo to the recent passage of the LMC. These particles reach speeds of 700-900 km/s with respect to the Earth, above the local escape speed of the MW. The high-speed particles follow trajectories similar to the Solar reflex motion, with peak velocities reached in June. For low-mass dark matter, these high-speed particles can dominate the signal in direct-detection experiments, extending the reach of the experiments to lower mass and elastic scattering cross sections even with existing data sets. Our study shows that even non-disrupted MW satellite galaxies can leave a significant dark-matter footprint in the Solar Neighborhood.

• The paper demonstrates that the high-velocity tail of local dark matter is primarily comprised of particles originating from the LMC, as revealed by tailored N-body simulations.
• The study finds that dark matter speeds between 700-900 km/s, driven by LMC and Milky Way dynamics, challenging standard Maxwell-Boltzmann velocity assumptions.
• Incorporating LMC contributions into detection models could enhance the sensitivity of experiments, particularly for lower-mass and low cross-section dark matter candidates.

Overview of "The highest-speed local dark matter particles come from the Large Magellanic Cloud"

The paper "The highest-speed local dark matter particles come from the Large Magellanic Cloud" by Besla et al. focuses on the dynamic interactions between the dark matter (DM) halo of the Milky Way (MW) and the Large Magellanic Cloud (LMC), leveraging N-body simulations to analyze these phenomena. The central claim of the paper is that the high-speed tail of the Solar Neighborhood dark matter distribution is largely comprised of particles originating from the LMC. This revelation has significant implications for dark matter detection experiments, which traditionally have not accounted for such contributions.

Key Findings

1. LMC as a Source of High-Speed Particles: The authors identify that particles contributing to the high-speed tail of the local dark matter distribution primarily originate from the LMC. They distinguish between:
   • LMC-bound particles that have escaped into the MW's halo.
   • MW halo particles that have been accelerated due to the gravitational influences exerted by the LMC's recent passage.
2. Velocity Characteristics: The paper finds that these particles can achieve speeds of 700-900 km/s relative to Earth, surpassing the local escape speed from the Milky Way, especially notable at particular times of the year (peaking in June).
3. Implications for Dark Matter Detection: These high-velocity particles have implications for direct detection experiments. Traditional models often assume a simple Maxwell-Boltzmann distribution for the velocity of dark matter particles, which does not consider these high-speed contributions. Consequently, incorporating LMC-originated dark matter could extend the sensitivity of these experiments down to lower mass and cross-sectional ranges for potential dark matter candidates.
4. Dynamic Modeling: By considering observational data to accurately model the orbits and masses of LMC and MW, the authors enhance the fidelity of their N-body simulations. This includes accounting for the MW's disk potential, velocity anisotropy, and the LMC's influence.

Computational Approach

The authors utilized high-resolution N-body simulations with specifically tailored initial conditions to reflect the observed properties of both galaxies. These simulations accounted for the interaction dynamics and subsequent distribution of dark matter particles in the Solar Neighborhood resulting from the LMC's infall.

Implications and Future Directions

The findings imply that current observational and experimental approaches to detecting dark matter signals could significantly underrepresent the actual dark matter profile in the Solar Neighborhood if LMC-originated particles are not considered. This suggests that future theoretical models and detection methods need to incorporate data-driven velocity distributions that account for LMC interactions, potentially revising the focus or methods used in dark matter research.

Furthermore, by identifying the LMC's contribution to the high-speed dark matter population, this paper offers an avenue for revising direct-detection prediction models, improving their accuracy, and potentially identifying lower-mass dark matter particles.

Conclusion

In summary, this paper underscores the importance of considering non-traditional dark matter sources, like the LMC, in shaping the Milky Way's halo dynamics. By recognizing these contributions, the research advances our understanding of how satellite galaxies influence galactic dynamics and dark matter detection scenarios, suggesting a revision of the current models used in interpreting experimental data. Future work could build upon this by better quantifying the interplay between other satellite galaxies and the MW's dark matter halo to further refine direct detection strategies.