Description
Recent basis function expansion models of perturbations to the Milky Way's outer halo offer new avenues to constrain the mass distribution. A key observable in this context is the reflex motion of the Milky Way disc with respect to its dark matter halo, induced by the LMC’s infall. In this work, we investigate the sensitivity of the reflex motion signal to different outer-halo profiles of the MW using a suite of basis function expansion simulations built with density-truncated NFW profiles. These profiles follow a broken power-law form, truncated beyond a characteristic break radius.
An analysis of the basis function coefficients reveals that stronger truncations (larger $\alpha$) produce a smaller dipole distortion , while the quadrupole distortion becomes more pronounced. These results highlight the limited constraining power of reflex motion amplitude alone for outer MW profile parameters. However, we also find a halo instability—whose oscillation frequency increases as $\alpha$ becomes more negative. This instability has a potentially observable signature - a radial sinusoidal pattern whose oscillation frequency increases as $\alpha$ becomes more negative.
