Johnny P. Greco, Paul Martini, Todd A. Thompson
We present a K-band spectroscopic study of the stellar and gas kinematics,
mass distribution, and stellar populations of the archetypical starburst M82.
We used the CO stellar absorption bandhead at 2.29 {\mu}m (CO_2.29) to measure
the rotation curve out to nearly 4 kpc radius on both the eastern and western
sides of the galaxy. In contrast with the nearly Keplerian gas dynamics
suggested by previous measurements of HI and CO emission from the ISM, which
imply a truncation in M82's dark matter halo, our data show that the rotation
curve is in fact flat on 1 - 4 kpc scales. The kinematics of the Br{\gamma},
H2, and HeI emission lines are consistent with, although characterized by
slightly higher velocities than, the stellar kinematics. We derived M82's mass
distribution from our stellar kinematic measurements and estimate its total
dynamical mass is ~10^10 Msun. We measured the equivalent width of CO_2.29
(W_2.29) as a function of distance from the center of the galaxy to investigate
the spatial extent of the red supergiant (RSG) population. The variation in
W_2.29 with radius clearly shows that RSGs dominate the light inside 500 pc
radius. M82's famous superwind is likely launched from this region, where we
estimate the enclosed mass is <= 2\times10^9 Msun.
View original:
http://arxiv.org/abs/1202.0824
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