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Session 63 - Galaxy Evolution II.
Oral session, Tuesday, January 16
Corte Real, Hilton
Hubble Space Telescope images of the Local Group dwarf galaxy Tucana reveal an unbiased sample of distant field galaxies. While a large number of these galaxies can be classified according to standard Hubble types, a significant number of these galaxies can be identified as ``ring'' galaxies, a morphology likely induced through galaxy collisions. We have identified eight collisional ring galaxy candidates in our fields. Assuming that these galaxies lie between the redshifts of 0.2 and 1, then if there has been no evolution in the galaxy interaction rate, the probability of finding a single ring galaxy in our field of view is less than 1%. Alternatively, if the interaction rate increases as (1 + z)^4.5, which represents a high-end estimate of the dependence of the galaxy merger rate on redshift, the probability increases to \sim10%. Thus, these observations suggest that in addition to an increased galaxy interaction rate at moderate redshifts, the types of interactions may also be evolving, with a higher frequency of low angular momentum, more radial galaxy collisions at earlier epochs.
