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Symposium 241

Abstract details

Star Formation History of Dwarfs in Nearby Galaxy Groups
Makarova L., Makarov D., Dolphin A., Karachentsev I., Tully R.B., Rizzi L., Sakai S., Shaya E.

About 200 nearby galaxies have already been observed with HST/WFPC2 and HST/ACS, either by our collaboration or by others, with data in the HST archive. This outstanding material includes images of galaxies of essentially all types, though dwarfs predominate. The galaxies are situated at a range of distances, mostly within 6 Mpc. Deep color-magnitude diagrams of resolved stars in these galaxies were analysed. We have developed software to obtain quantitative star formation histories of the dwarfs. We create a library of synthetic color-magnitude diagrams from theoretical stellar isochrones, taking the initial mass function, distance to the galaxy, internal and external absorption, and photometric errors into account. The resulting synthetic diagrams are combined linearly and compared quantitatively with photometric data for stars in a galaxy in order to determine star formation rates as a function of age and metallicity. Star formation histories of several galaxies in the two nearby groups of galaxies: Cen A and M 81 are presented. We detect complex star formation in the galaxies under consideration.

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