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Proposal Information for 2003A-0286


PI: Andrew Dolphin, NOAO, dolphin@noao.edu
Address: KPNO, PO Box 26732, Tucson, AZ 85726, USA

CoI: Abi Saha, NOAO

Title: Leo I: The Dwarf Galaxy Evolutionary Link?

Abstract: The morphological classifications of dwarf galaxies into irregulars (gas-rich galaxies actively forming stars) and spheroidals (predominantly-ancient systems with no star formation) has long been accepted as a division between two fundamentally-distinct classes of objects. However, recent evidence has begun to accumulate that some irregulars have recently ceased star formation and that some spheroidals were actively forming stars until a few Gyr ago. This raises the possibility that, rather than being fundamentally distinct classes of galaxies, irregular and spheroidal galaxies represent two phases along a dwarf galaxy evolutionary sequence. Leo I appears to be the galaxy providing the link between the two classes of dwarf galaxies. While its morphology resembles that of a spheroidal galaxy and it is classified as such, it contains main sequence stars as bright as M_V=0. While star formation history calculations for the central region indicate the presence of large number of stars as young as 1 Gyr, it is clear from CMDs of outer regions that Leo I does not have a uniform distribution of stellar populations and thus that its star formation history (and consequently its potential place as an evolutionary link between the irregular and spheroidal galaxies) cannot be understood until deep CMDs have been obtained that sample the entire galaxy. The density of stars, distance, and proximity to Regulus have prohibited such a study in the past. We propose to make such a study using the new tip-tilt module at WIYN, which provides excellent image quality and contains a pupil mask to provide the necessary baffling.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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