Zw 0855+06: A Wolf-Rayet dwarf galaxy triggered by a dwarf-dwarf interaction

We present narrowband (H alpha and adjacent continuum) and broadband (B and V) optical images of the dwarf Wolf-Rayet galaxy Zw 0855 + 06 and its comp anion, together with high-resolution H alpha spectroscopy of the main galax y. We find a bridge of similar to 14.7 kpc (similar to 65 ") in length and stellar nature connecting both galaxies, a feature that undoubtedly indicat es their mutual interaction. We infer from the narrow width of the bridge t hat at least one of these two dwarf galaxies had a well-developed disk befo re the interaction. The light of the main galaxy (M-B = - 17.82) is dominat ed by a young and massive ionizing population. There is ample reason to bel ieve that a gravitational interaction with the companion caused the starbur st. The companion (M-B = -15.84) does not show any evidence of ionized gas, and its population has a B-V color that suggests the presence of intermedi ate-age (similar to 10(9) yr) stars. This case highlights the concept that bursts in H II dwarf galaxies may be caused by interactions with lower lumi nosity companions. We anticipate that ruling out interactions as the origin of bursts in dwarf galaxies will require deeper surveys than are currently available. We find a backward outflow with a velocity of about 47 km s(-1) in the southeast part (similar to 880 pc from the center) of the main gala xy, suggesting the presence of dynamical effects on the interstellar gas ar ising from the mechanical action of the massive stars or the interaction pr ocess.