Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2012-02-03
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
6 pages, 6 figures. Submitted to ApJ. For a brief video explaining the key result of this paper, see http://www.youtube.com/us
Scientific paper
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.
Greco Johnny P.
Martini Paul
Thompson Todd A.
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