Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-08-13
Astrophys.J.634:281-286,2005
Astronomy and Astrophysics
Astrophysics
To be published in ApJ, Nov 2005
Scientific paper
10.1086/496949
We present measurements of the stellar velocity dispersion in the inner 1 arcmin radius (1.3 disk scale-lengths) of the irregular galaxy NGC 4449 determined from long-slit absorption-line spectra. The average observed dispersion is 29 +/-2 km/s, the same as predicted from NGC 4449's luminosity. No significant rotation in the stars is detected. If we assume a maximum rotation speed of the stars from the model determined from the gas kinematics of Hunter et al. (2002), the ratio V_max/sigma_z measured globally is 3. This ratio is comparable to values measured in spiral galaxies, and implies that the stellar disk in NGC 4449 is kinematically relatively cold. The intrinsic minor-to-major axis ratio (b/a)_0 is predicted to be in the range 0.3-0.6, similar to values derived from the distribution of observed b/a of Im galaxies. However, V/sigma_z measured locally is 0.5-1.1, and so the circular velocity of NGC 4449 is comparable or less than the velocity of the stars within the central 1.3 disk scale-lengths of the galaxy.
Hunter Deidre Ann
Levine Stephen E.
Rubin Vera Cooper
Sparke Linda S.
Swaters Rob A.
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