Kavli Affiliate: Risa H. Wechsler
| First 5 Authors: Elise Darragh-Ford, Elise Darragh-Ford, , ,
| Summary:
The distribution of dark matter in the Milky Way (MW) is expected to exhibit
a large-scale dynamical response to the recent infall of the LMC. This event
produces a dynamical friction wake and shifts the MW’s halo density center. The
structure of this response encodes information about the LMC- MW mass ratio,
the LMC’s orbit, the MW halo’s pre-infall structure and could provide
constraints on dark matter physics. To extract this information, a method to
separate these effects and recover the initial shape of the MW’s halo is
required. Here, we use basis function expansions to analyze the halo response
in eighteen simulations of MW-LMC-like interactions from the MWest
cosmological, dark-matter-only zoom-in simulations. The results show that
mergers similar to the LMC consistently generate a significant dipole and a
secondary quadrupole response in the halo. The dipole arises from the host
density center displacement and halo distortions, and its amplitude scales as
the square of the MW-LMC mass ratio, peaking 0.2-0.7 Gyr after the LMC’s
pericenter. The quadrupole’s strength depends primarily on the original axis
ratios of the host halo, though contributions from the dynamical friction wake
cause it to peak less than 0.3 Gyr before pericenter. Future measurements of
both the dipole and quadrupole imprints of the LMC’s passage in the density of
the MW’s stellar halo should be able to disentangle these effects and provide
insight into the initial structure of the MW’s halo, the MW’s response, and the
mass of the LMC.
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