Transmission and amplification of disturbances by massive halos

We study how massive halos respond to perturbations. Through numerical solution of the coupled linearized Boltzmann-Poisson equations, we find that halos can transmit and amplify disturbances over large distances within galaxies. In particular, as Weinberg has noted, the halo provides an excellent medium for transmitting disturbances from the outer regions of galaxies to the inner regions. The dipolar response typically dominates and, in some cases, is very weakly damped. The monopole and quadrupole response can also make significant contributions. Overall, the results support the notion that disk structure can be excited by transmission of noise from the distant halo. The strong dipolar response suggests that halos play a role in producing lopsided disks. These results also suggest that, during formation from initial collapse, halos do not settle rapidly into static equilbrium; instead, they may continue to ring and interact with other embryonic components of proto-galaxies. Subject headings: stellar dynamics – galaxies: individual (Milky Way) – galaxies: haloes – galaxies: kinematics and dynamics