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Session 63 - Galaxy Evolution II.
Oral session, Tuesday, January 16
Corte Real, Hilton
We present here the preliminary results of an investigation into star formation properties of HI rich, low surface brightness dwarf galaxies in which past star formation may have been suppressed. Our targets were identified via a systematic survey for extended HI envelopes around low luminosity objects with the Arecibo telescope. The main goals of this study are: to constrain the past star formation history from optical broad band colors and element abundances; (2) to determine the state of collapse from the gas dynamics and kinematics; (3) to investigate the possibility that these systems have not been able to efficiently convert their gas into stars because the majority of the gas is below the threshold necessary for star formation. In order to determine the evolutionary history of these objects, detailed data sets have been obtained. HI VLA maps were used to derive gas kinematics and dynamics as well as to compare the gas distribution relative to sites of current star formation. As expected, the majority of the HI gas may be below the threshold required for star formation while the current star formation knots are located near, but slightly offset from, the peaks in the HI column density. Both the current star formation rate and elemental abundances in the HII regions, as derived from high sensitivity optical spectra, are low. Optical colors, derived from photometric UBVR imaging, were used to constrain the ages of the stellar population in both high and low surface brightness regions. The optical colors are consistent with a suppressed, but constant, star formation history over the last few Gyr.
