GALAXIES WITH SPECTRAL ENERGY-DISTRIBUTIONS PEAKING NEAR 60 MU-M .3. H-ALPHA IMAGING

We present the results of our Ha imaging survey of galaxies with far-infrared (FIR) spectral energy distributions (SEDs) peaking near 60 μm (60 PKs). The Hα emission is found to be strongly centrally concentrated with a linear extent of at most a few kpc, similar to that of the radio continuum emission. The central concentration is more pronounced for Seyfert than H II region-like 60 PKs. For the former the extent of the Hα emitting region is comparable to the typical size of the narrow emission-line region of active galaxies The central region of 60 PKs is thus dominated by a strong nonthermal or starburst source that is heavily obscured at optical wavelengths. The central ionizing source and the obscuring dust are responsible for the 60 PK phenomenon and the associated FIR emission and FIR to Hα luminosity ratio. These results support our interpretation of observational data presented in previous papers in this series [Vader et al. AJ, 106, 1743 (1993)]; Heisler & Vader, AJ, 107, 35 (1994)] that galaxies with far-infrared (FIR) spectral energy distributions peaking near 60 μm are undergoing a short-lived phase of central activity, resulting from an interaction/merger event. © 1995 American Astronomical Society.