paper

The little galaxy that could: Kinematics of Camelopardalis B

arXiv:astro-ph/0301194 · doi:10.1016/S1384-1076(02)00238-5

Abstract

We present deep, high velocity resolution (1.6 km/s) GMRT HI as well as optical data for the faint (M_B ~ -10.9) galaxy Camelopardalis B. We find that the HI in the galaxy has a regular velocity field, consistent with rotational motion. The implied kinematical major axis is well aligned with the major axis of both the HI and optical images. Cam B is the faintest known galaxy with such relatively well behaved kinematics. From the HI velocity field we derive a rotation curve for the galaxy. The peak (inclination corrected) rotation velocity is only 7km/s, comparable to the observed velocity dispersion. After correcting the observed rotation velocities for random motions (the "asymmetric drift" correction) we find a corrected peak rotation velocity of ~ 20 km/s. On fitting mass models to corrected rotation curve we find that the kinematics of Cam B is well fit with a modified isothermal halo with central density approximately 12.0 pc. This derived central density has only a very weak dependence on the assumed M/L ratio of the stellar disk. We also find that the corrected rotation curve cannot be fit with an NFW halo regardless of the assumed M/L ratio. We compile from the literature a sample of galaxies with rotation curves obtained from HI synthesis observations. From this sample (which has an absolute magnitude range of ~ 12) we find (i) that Cam B lies on the Tully-Fisher relation defined by these galaxies, provided we use the corrected rotation velocity, and (ii) a weak trend for increasing halo central density with decreasing galaxy size. Such a trend is expected in hierarchical models of halo formation.

Accepted for publication in New Astronomy. For copyright reasons this version is slightly different from the accepted version, although the differences are minor

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