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Session 6 - Evolution, Survey and Clusters of Galaxies.
Display session, Monday, June 10
The morphological classification of nearby normal galaxies is embodied in the Hubble system, in which galaxies range from ellipticals through spirals to irregulars. Some galaxies, however, do not fit neatly into any of the Hubble categories. These peculiar galaxies play an important role in our understanding of the evolution of galaxies.
Peculiarities in the morphology of galaxies are now believed to be primarily a result of galaxy interactions and mergers. For example, gravitational tides between interacting galaxies cause morphological distortions and shocks, which can in turn induce bursts of star formation. The frequency of peculiar galaxies at a given epoch likely reflects the merger rate at that epoch. The nature and degree of the peculiarities may give us an indication of the types of mergers that have occurred and the relative masses and other properties of the progenitors.
From early deep HST images, the frequency of peculiar galaxies at high redshifts has been claimed to be much higher than it is locally (eg, Forbes et al. 1994, Driver et al. 1995, Cowie et al. 1995). Nevertheless, little has been done to quantify the types and degrees of peculiarities that are seen.
I am currently developing several mathematical algorithms which will be applied to galaxy images and are sensitive to several different types of peculiarities (eg, rattiness of the surface brightness contours, multimodality, strength of the corridor between interacting galaxies). Preliminary results of a subset of these peculiarity indices will be presented. I will also simulate distant galaxies by adding noise to and rebinning images of local galaxies to match the signal-to-noise ratio and sampling of distant images. These ``redshifted'' images will be used to explore how the values of the peculiarity indices change for various types of local galaxies as they are redshifted to high redshifts.
Program listing for Monday