The Stellar and Gaseous Contents of the Orion Dwarf Galaxy

TL;DR

This study provides detailed optical and radio observations of the Orion dwarf galaxy, revealing its gas structure, rotation dynamics, dark matter content, and modest current star formation activity.

Contribution

It offers new high-resolution data on the galaxy's neutral gas, kinematics, dark matter distribution, and star formation, enhancing understanding of dwarf galaxy properties.

Findings

Presence of three HI depression features in the galaxy.

Flat rotation curve extending to 6.8 kpc.

Modest current star formation rate of 0.04 solar masses per year.

Abstract

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.