We perform a set of high-resolution, dissipationless N-body simulations to
investigate the influence of cold dark matter (CDM) substructure on the
dynamical evolution of thin galactic disks. Our method combines cosmological
simulations of galaxy-sized CDM halos to derive the properties of substructure
populations and controlled numerical experiments of consecutive subhalo impacts
onto initially-thin, fully-formed disk galaxies. We demonstrate that close
encounters between massive subhalos and galactic disks since z~1 should be
common occurrences in LCDM models. In contrast, extremely few satellites in
present-day CDM halos are likely to have a significant impact on the disk
structure. One typical host halo merger history is used to seed controlled
N-body experiments of subhalo-disk encounters. As a result of these accretion
events, the disk thickens considerably at all radii with the disk scale height
increasing in excess of a factor of 2 in the solar neighborhood. We show that
interactions with the subhalo population produce a wealth of distinctive
morphological signatures in the disk stars including: conspicuous flares; bars;
low-lived, ring-like features in the outskirts; and low-density, filamentary
structures above the disk plane. We compare a resulting dynamically-cold,
ring-like feature in our simulations to the Monoceros ring stellar structure in
the MW. The comparison shows quantitative agreement in both spatial
distribution and kinematics, suggesting that such observed complex stellar
components may arise naturally as disk stars are excited by encounters with
subhalos. These findings highlight the significant role of CDM substructure in
setting the structure of disk galaxies and driving galaxy evolution.Comment: 10 pages, 4 figures. To appear in the proceedings of the IAU
Symposium No. 254 "The Galaxy Disk in Cosmological Context", Copenhagen 9-13
June 2008, Denmark, (Eds.) J. Andersen, J. Bland-Hawthorn & B. Nordstrom,
Cambridge University Pres