We present new KPNO 0.9-m optical and VLA HI spectral line observations of
the Orion dwarf galaxy. This nearby (D ~ 5.4 Mpc), intermediate-mass (M_dyn =
1.1x10^10 Solar masses) dwarf displays a wealth of structure in its neutral
ISM, including three prominent "hole/depression" features in the inner HI disk.
We explore the rich gas kinematics, where solid-body rotation dominates and the
rotation curve is flat out to the observed edge of the HI disk (~6.8 kpc). The
Orion dwarf contains a substantial fraction of dark matter throughout its disk:
comparing the 4.7x10^8 Solar masses of detected neutral gas with estimates of
the stellar mass from optical and near-infrared imaging (3.7x10^8 Solar masses)
implies a mass-to-light ratio of ~13. New H alpha observations show only
modest-strength current star formation (~0.04 Solar masses per year); this star
formation rate is consistent with our 1.4 GHz radio continuum non-detection.Comment: Astronomical Journal, in press. Full-resolution version available
from http://www.macalester.edu/~jcannon/pubs.htm
