Cold Dark Matter Substructure and Galactic Disks II: Dynamical Effects
  of Hierarchical Satellite Accretion
  (Abridged) We perform dissipationless N-body simulations to elucidate the
dynamical response of thin disks to bombardment by cold dark matter (CDM)
substructure. Our method combines (1) cosmological simulations of the formation
of Milky Way (MW)-sized CDM halos to derive the properties of substructure and
(2) controlled numerical experiments of consecutive subhalo impacts onto an
initially-thin, fully-formed MW type disk galaxy. The present study is the
first to account for the evolution of satellite populations over cosmic time in
such an investigation of disk structure. We find that accretions of massive
subhalos onto the central regions of host halos, where the galactic disks
reside, since z~1 should be common. One host halo accretion history is used to
initialize the controlled simulations of satellite-disk encounters. We show
that these accretion events severely perturb the thin galactic disk and produce
a wealth of distinctive dynamical signatures on its structure and kinematics.
These include (1) considerable thickening and heating at all radii, with the
disk thickness and velocity ellipsoid nearly doubling at the solar radius; (2)
prominent flaring associated with an increase in disk thickness greater than a
factor of 4 in the disk outskirts; (3) surface density excesses at large radii,
beyond ~5 disk scale lengths, resembling those of observed antitruncated disks;
(4) lopsidedness at levels similar to those measured in observational samples
of disk galaxies; and (5) substantial tilting. The interaction with the most
massive subhalo drives the disk response while subsequent bombardment is much
less efficient at disturbing the disk. We conclude that substructure-disk
encounters of the kind expected in the LCDM paradigm play a significant role in
setting the structure of disk galaxies and driving galaxy evolution.
