The impact of the Large Magellanic Cloud on dark matter direct detection signals

Abstract

We study the effect of the Large Magellanic Cloud (LMC) on the dark matter (DM) distribution in the Solar neighborhood, utilizing the Auriga magneto-hydrodynamical simulations of Milky Way (MW) analogues that have an LMC-like system. We extract the local DM velocity distribution at different times during the orbit of the LMC around the MW in the simulations. As found in previous idealized simulations of the MW-LMC system, we find that the DM particles in the Solar neighborhood originating from the LMC analogue dominate the high speed tail of the local DM speed distribution. Furthermore, the native DM particles of the MW in the Solar region are boosted to higher speeds as a result of a response to the LMC's motion. We simulate the signals expected in near future xenon, germanium, and silicon direct detection experiments, considering DM interactions with target nuclei or electrons. We find that the presence of the LMC causes a considerable shift in the expected direct detection exclusion limits towards smaller cross sections and DM masses, with the effect being more prominent for low mass DM. Hence, our study shows, for the first time, that the LMC's influence on the local DM distribution is significant even in fully cosmological MW analogues.

Milky Way-est: Cosmological Zoom-in Simulations with Large Magellanic Cloud and Gaia–Sausage–Enceladus Analogs

“…It is interesting to consider how many of (and how accurately) the MW's major accretion events must be modeled to meet the precision of upcoming MW dwarf galaxy and stellar stream observations. On even smaller, subkiloparsec scales, stellar velocity distributions near the solar circle and dark matter direct-detection experiments are sensitive to substructure accreted during specific merger and accretion events like the GSE and LMC (e.g., Necib et al 2019;Besla et al 2019;Smith-Orlik et al 2023). This motivates studies of the local dark matter distribution using Milky Way-est.…”

“…Motivated by the observational advances discussed above, recent simulations have focused on halos that satisfy additional constraints on the MW's merger history. Considering the LMC, several authors have analyzed small numbers of MW-mass hosts with LMC analog subhalos using gravity-only (e.g., Erkal & Belokurov 2020;Sales et al 2017) or hydrodynamic simulations (e.g., Barry et al 2023;Smith-Orlik et al 2023;Arora et al 2023). Considering GSE and other early accretion events, Bignone et al (2019) and Bose et al (2020) study hosts in cosmological hydrodynamic simulations that include GSE analogs, Rey et al (2023) present zoom-in simulations that are engineered to include GSE analogs with controlled properties, and García-Bethencourt et al (2023) present a high-resolution hydrodynamical simulation that includes analogs of the GSE and the early Kraken and Sequoia mergers.…”

Are there any extragalactic high speed dark matter particles in the Solar neighborhood?

“…Amongst the 8 primary halos in the four APOSTLE volumes studied here (AP-1, AP-4, AP-6, and AP-11), 4 of them have a satellite as massive as the LMC, although they may not match the current position and velocity of the LMC [13,29]. There has been no attempt in APOSTLE to match other observational constraints on larger scales, like the presence of nearby groups such as M81 and Cen A; the Virgo cluster; or the Supergalactic Plane.…”

“…This estimate of the local maximum DM speed depends critically on the maximum circular velocity assumed, as well as on the assumption that the Solar neighborhood is close to equilibrium. Strong transients, such as the recent arrival of the Magellanic Clouds into the Milky Way halo, could result in large fluctuations in the halo, causing significant shifts in the high-speed tail of the local DM velocity distribution that have been recently studied in both idealized and cosmological simulations [13][14][15].…”

“…In addition, simulations studying the effect of large satellite galaxies such as the Large Magellanic Cloud (LMC) on the MW show that the LMC significantly impacts the high velocity tail of the local DM velocity distribution, shifting it to higher speeds [13][14][15]. This has strong consequences for the interpretation of results from direct detection experiments, leading to considerable shifts of the direct detection exclusion limits towards smaller DM-nucleon or DM-electron cross sections and DM masses.…”