The Sphericalization of Dark Matter Halos by Galaxy Disks
  Cosmological simulations indicate that cold dark matter (CDM) halos should be
triaxial. Verifying observationally this theoretical prediction is, however,
less than straightforward because the assembly of galaxies is expected to
modify the halo shapes and to render them more axisymmetric. We use a suite of
N-body simulations to investigate quantitatively the effect of the growth of a
central disk galaxy on the shape of triaxial dark matter halos. As expected,
the halo responds to the presence of the disk by becoming more spherical. The
net effect depends only weakly on the orientation of the disk relative to the
halo principal axes or the timescale of disk assembly, but strongly on the
overall gravitational importance of the disk. Our results show that exponential
disks whose contribution peaks at less than ~50% of their circular velocity are
unable to modify noticeably the shape of the gravitational potential of their
surrounding halos. Many dwarf and low surface brightness galaxies are expected
to be in this regime, and therefore their detailed kinematics could be used to
probe halo triaxiality, one of the basic predictions of the CDM paradigm. We
argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be
the reflection of a triaxial halo. Such signatures of halo triaxiality should
be common in galaxies where the luminous component is subdominant.
