Kinematics and Mass Modeling of Messier 33: Halpha observations
  As part of a long-term project to revisit the kinematics and dynamics of the
large disc galaxies of the Local Group, we present the first deep, wide-field
(42' x 56') 3D-spectroscopic survey of the ionized gas disc of Messier 33.
Fabry-Perot interferometry has been used to map its Ha distribution and
kinematics at unprecedented angular resolution (<3'') and resolving power
(12600), with the 1.6m telescope at the Observatoire du Mont Megantic. The
ionized gas distribution follows a complex, large-scale spiral structure,
unsurprisingly coincident with the already-known spiral structures of the
neutral and molecular gas discs. The kinematical analysis of the velocity field
shows that the rotation center of the Ha disc is distant from the photometric
center by 170 pc (sky projected distance) and that the kinematical major-axis
position angle and disc inclination are in excellent agreement with photometric
values. The Ha rotation curve agrees very well with the HI rotation curves for
0 < R < 6.5 kpc, but the Ha velocities are 10-20 km/s higher for R > 6.5 kpc.
The reason for this discrepancy is not well understood. The velocity dispersion
profile is relatively flat around 16 km/s, which is at the low end of velocity
dispersions of nearby star-forming galactic discs. A strong relation is also
found between the Ha velocity dispersion and the Ha intensity. Mass models were
obtained using the Ha rotation curve but, as expected, the dark matter halo's
parameters are not very well constrained since the optical rotation curve only
extends out to 8 kpc.
