Exploring the mass assembly of the early-type disc galaxy NGC3115 with
  MUSE
  We present MUSE integral field spectroscopic data of the S0 galaxy NGC 3115
obtained during the instrument commissioning at the ESO Very Large Telescope
(VLT). We analyse the galaxy stellar kinematics and stellar populations and
present two dimensional maps of their associated quantities. We thus illustrate
the capacity of MUSE to map extra-galactic sources to large radii in an
efficient manner, i.e., ~4 Re, and provide relevant constraints on its mass
assembly. We probe the well known set of substructures of NGC 3115 (its nuclear
disc, stellar rings, outer kpc-scale stellar disc and spheroid) and show their
individual associated signatures in the MUSE stellar kinematics and stellar
populations maps. In particular, we confirm that NGC 3115 has a thin fast
rotating stellar disc embedded in a fast rotating spheroid, and that these two
structures show clear differences in their stellar age and metallicity
properties. We emphasise an observed correlation between the radial stellar
velocity, V, and the Gauss-Hermite moment, h3, creating a "butterfly" shape in
the central 15" of the h3 map. We further detect the previously reported weak
spiral and ring-like structures, and find evidence that these features can be
associated with regions of younger mean stellar ages. We provide tentative
evidence for the presence of a bar, despite the fact that the V-h3 correlation
can be reproduced by a simple axisymmetric dynamical model. Finally, we present
a reconstruction of the two dimensional star formation history of NGC 3115 and
find that most of its current stellar mass was formed at early epochs (>12Gyr
ago), while star formation continued in the outer (kpc-scale) stellar disc
until recently. Since z~2, and within ~4 Re, we suggest that NGC 3115 has been
mainly shaped by secular processes.
