SDSS-IV MaNGA: The intrinsic shape of slow rotator early-type galaxies
  By inverting the distributions of galaxies' apparent ellipticities and
misalignment angles (measured around the projected half-light radius $R_{\rm
e}$) between their photometric and kinematic axes, we study the intrinsic shape
distribution of 189 slow rotator early-type galaxies with stellar masses
$2\times 10^{11} M_{\odot}<M_\ast<2\times 10^{12} M_{\odot}$, extracted from a
sample of about 2200 galaxies with integral-field stellar kinematics from the
DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow
rotators, Graham+18 showed that there is clear structure in the misalignment
angle distribution, with two peaks at both $0^{\circ}$ and $90^{\circ}$
misalignment (characteristic of oblate and prolate rotation respectively). Here
we invert the observed distribution from Graham+18. The large sample allows us
to go beyond the known fact that slow rotators are weakly triaxial and to place
useful constraints on their intrinsic triaxiality distribution (around $1R_{\rm
e}$) for the first time. The shape inversion is generally non-unique. However,
we find that, for a wide set of model assumptions, the observed distribution
clearly requires a dominant triaxial-oblate population. For some of our models,
the data suggest a hint for a minor triaxial-prolate population, but a dominant
prolate population is ruled out.
