Uncovering the Intrinsic Shapes of Elliptical Galaxies
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**Session 17 -- Normal Galaxies**
*Oral presentation, Monday, 10:30-12:00, Wheeler Room*

## [17.04] Uncovering the Intrinsic Shapes of Elliptical Galaxies

*T. Statler (UNC Chapel Hill)*
The true shapes of elliptical galaxies cannot be determined from photometric
data alone. Here I present a new general method for constraining the
intrinsic shapes of ellipticals through their apparent shapes and kinematics.
At its heart is a set of theoretical models for radial velocity fields,
constructed by solving the equation of continuity for the mean flow of the
stellar ``fluid''. The radial luminosity profile, halo density profile,
axis ratios, rotation axis, and other dynamical parameters may be chosen
freely; radial mean motions induced by aspherical dark halos can be included.
The primary simplifying assumption is that the three-dimensional flow field
is similar at all radii well outside the core. The models are both more
general and much easier to calculate than the existing, very restrictive,
self-consistent models. The quick computability makes it possible to develop
a procedure of Monte Carlo model fitting that compares models and real
galaxy data in a statistically rigorous way. Typically $10^7$ individual
models are compared against the data in a complete shape fit. It is found
that, with standard photometry and high-quality kinematics at 4 position
angles, the shapes of individual ellipticals can be estimated despite
ignorance of their detailed internal dynamics and halo structure. This claim
is illustrated with the E2 galaxy NGC 4589. The dynamical triaxiality $T$ and
the flattening of the light distribution $c_L$ are found to be $T = 0.63
\ ^{+.28}_{-.43}$, $c_L = 0.80 \ ^{+.05}_{-.12}$ ($1\sigma$ errors), making
the most probable shape prolate-triaxial. The dominant source of error is in
the measured velocities. Reducing the errors to 15\% of the maximum rotation
velocity would shrink the uncertainty in shape by a factor of 2. Results for
the Virgo elliptical NGC 4472 (M49) are also presented.

**Monday
program listing**