Photometric signatures of starbursts in interacting galaxies and the Butcher-Oemler effect

This paper presents new and synthetic narrowband photometry of ellipticals, spirals, Seyferts, and interacting galaxies in an attempt to identify the cause of the unusually high fraction of blue cluster galaxies in distance clusters (Butcher-Oemler effect). The properties and distribution of the low-redshift sample specifically points to starbursts as the origin of the blue narrowband colors in interacting Arp galaxies. Comparison between theoretical models and multicolor diagrams, particularly 4000 Angstrom break colors, indicates a photometric signature that differs from both normal disk galaxy star formation and nonthermal components. This photometric signature is absent for the Butcher-Oemler galaxies whose general color distribution, compared to present-day clusters, is consistent with a majority of the blue population involved in normal star formation rates (spiral-like) with the addition of a small fraction of bright, blue interacting/merger systems. This photometric picture of the Butcher-Oemler galaxies is in agreement with the morphological evidence from Hubble Space Telescope imaging.