We investigate how the shapes and angular momenta of galaxy and group mass dark matter halos in a \mathrm { \Lambda } CDM N -body simulation are correlated internally , and how they are aligned with respect to the location and properties of surrounding halos .
We explore these relationships down to halos of much lower mass ( 10 ^ { 11 } ~ { } h ^ { -1 } ~ { } \mathrm { M _ { \sun } } ) than previous studies .
The halos are triaxial , with c / a ratios of 0.6 \pm 0.1 and a mean two-dimensional projected ellipticity of \left < e \right > = 0.24 .
More massive halos are more flattened .
The axis ratios rise out to 0.6 r _ { \mathrm { vir } } , beyond which they drop .
The principal axes , in particular the minor axes , are very well aligned within 0.6 r _ { \mathrm { vir } } .
High mass halos show particularly strong internal alignment .
The angular momentum vectors are also reasonably well aligned except between the very outermost and very innermost regions of the halo .
The angular momentum vectors tend to align with the minor axes , with a mean misalignment of \sim 25 \arcdeg , and lie perpendicular to the major and intermediate axes .
The properties of a halo at 0.4 r _ { \mathrm { vir } } are quite characteristic of the properties at most other radii within the halo .
There is a very strong tendency for the minor axes of halos to lie perpendicular to large scale filaments , and a much weaker tendency for the major axes to lie along the filaments .
This alignment extends to much larger separations for group and cluster mass halos than for galaxy mass halos .
As a consequence , the intrinsic alignments of galaxies are likely weaker than previous predictions , which were based on the shapes of cluster mass halos .
The angular momenta of the highest concentration halos tend to point toward other halos .
The angular momenta of galaxy mass halos point parallel to filaments , while those of group and cluster mass halos show a very strong tendency to point perpendicular to the filaments .
This suggests that group and cluster mass halos acquire most of their angular momentum from major mergers along filaments , while the accretion history of mass and angular momentum onto galaxy mass halos has been smoother .