The Atlas3D project - XII. Recovery of the mass-to-light ratio of
  simulated early-type barred galaxies with axisymmetric dynamical models
  We investigate the accuracy in the recovery of the stellar dynamics of barred
galaxies when using axisymmetric dynamical models. We do this by trying to
recover the mass-to-light ratio (M/L) and the anisotropy of realistic galaxy
simulations using the Jeans Anisotropic Multi-Gaussian Expansion (JAM) method.
However, given that the biases we find are mostly due to an application of an
axisymmetric modeling algorithm to a non-axisymmetric system and in particular
to inaccuracies in the de-projected mass model, our results are relevant for
general axisymmetric modelling methods. We run N-body collisionless simulations
to build a library with various luminosity distribution, constructed to mimic
real individual galaxies, with realistic anisotropy. The final result of our
evolved library of simulations contains both barred and unbarred galaxies. The
JAM method assumes an axisymmetric mass distribution, and we adopt a spatially
constant M/L and anisotropy beta_z=1-sigma_z^2/sigma_R^2 distributions. The
models are fitted to two-dimensional maps of the second velocity moments
V_rms=sqrt(V^2+sigma^2) of the simulations for various viewing angles (position
angle of the bar and inclination of the galaxy). We find that the inclination
is generally well recovered by the JAM models, for both barred and unbarred
simulations. For unbarred simulations the M/L is also accurately recovered,
with negligible median bias and with a maximum one of just Delta(M/L)<1.5% when
the galaxy is not too close to face on. At very low inclinations (i<30 deg) the
M/L can be significantly overestimated (9% in our tests, but errors can be
larger for very face-on views). For barred simulations the M/L is on average
(when PA=45 deg) essentially unbiased, but we measure an over/under estimation
of up to Delta(M/L)=15% in our tests. The sign of the M/L bias depends on the
position angle of the bar as expected. [Abridged]
