AbstractWe discuss our program of narrow-band (Hα + [Nil]) imaging of a sample of 30 powerful far-infrared galaxies (FIRG’s) chosen to have far-infrared spectral energy distributions similar to the prototype FIRG’s Arp 220, NGC 3690, NGC 6240, and M82. The emission-line nebulae of these IR color-selected sample (ICSS) galaxies as a class are both impressively large (mean half light radius, r ~1.3 Kpc, and mean diameter, D ~16 Kpc) and luminous (LTOT ~108 Lo; uncorrected for internal extinction). The mean total Hα + [Nil] luminosity of the FIRG’s is comparable to that found for pairs of optically selected interacting galaxies (Bushouse, Lamb, and Werner 1988), but is a factor of ~5 greater than that of isolated spirals (Kennicutt and Kent 1983). Only ~25% of the nearby (z ≤ 0.10) FIRG’s have morphologies suggesting that large HII~regions contribuí significantly to their emission-line appearance. The broad-band morphologies of our IR color-selected galaxies fall into three major categories. Nearly 75% are single galaxy systems, with the remaining FIRG’s being either multiple nuclei systems, or members of interacting pairs. Since we see few (10%) currently interacting FIRG’s, yet many (80%) with highly distorted continuum morphologies, our IR color criteria may be preferentially selecting galaxies that have undergone highly inelastic, rapidly merging interactions.
The Nature of the Emission-line Nebulae in Powerful Far-infrared Galaxies