Discovery of a double ring in the dwarf galaxy Markarian 409

Abstract

We report the discovery of a double ring of emission-line regions around the nucleus of the blue compact dwarf galaxy Mrk 409 as seen by deep, ground-based Hα images. Echelle spectroscopy obtained at Magellan I with MIKE shows the presence of ionized gas flowing out of the galaxy from a very massive (≥7 × 10^6 M_☉) nuclear starburst with projected expansion velocities of ~50 km s-^1. Different scenarios for the formation of these rings are discussed. While the innermost, nuclear ring is most probably formed by the interaction of a starburst-driven shock with the surrounding interstellar medium, the origin of the outer ring is less clear.