We conduct a series of high-resolution , fully self-consistent dissipationless N -body simulations to investigate the cumulative effect of substructure impacts onto thin disk galaxies in the context of the \Lambda CDM paradigm of structure formation .
Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments .
Substructure mass functions , orbital distributions , internal structures , and accretion times are culled directly from cosmological simulations of galaxy-sized cold dark matter ( CDM ) halos .
We demonstrate that accretions of massive subhalos onto the central regions of host halos , where the galactic disk resides , since z \sim 1 should be common occurrences .
In contrast , extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure .
This is due to the fact that massive subhalos with small orbital pericenters that are most capable of strongly perturbing the disk become either tidally disrupted or suffer substantial mass loss prior to z = 0 .
One host halo merger history is subsequently used to seed controlled N -body experiments of repeated satellite encounters with an initially-thin galactic disk .
These simulations track the effects of six dark matter substructures , with initial masses in the range \sim ( 0.7 - 2 ) \times 10 ^ { 10 } { M _ { \odot } } ( \sim 20 - 60 \% of the disk mass ) , crossing the disk in the past \sim 8 Gyr .
We demonstrate that these accretion events produce several distinctive morphological signatures in the stellar disk including : long-lived , low-surface brightness , ring-like features in the outskirts ; significant flares ; bars ; and faint filamentary structures that ( spuriously ) resemble tidal streams in configuration space .
The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard “ thin-thick ” disk decomposition , where the “ thick ” disk component has emerged primarily as a result of the interaction with the most massive subhalo .
Though our simulation campaign was not designed to elucidate the nature of specific Galactic structures , we compare one of the resulting dynamically cold ring-like features in our simulations to the Monoceros ring stellar structure in the Milky Way ( 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 CDM substructure .
We conclude that satellite-disk interactions of the kind expected in \Lambda CDM models can induce morphological features in galactic disks that are similar to those being discovered in the MW , M31 , and in other nearby and distant disk galaxies .
These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution .
Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm .