Star Formation Histories of Dwarf Galaxies in the Local Group

Details Star Formation Histories of Dwarf Galaxies in the Local Group Star Formation Histories of Dwarf Galaxies in the Local Group

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sgyu.conf..147a&link_type=abstract

Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar, held in Sendai, Ja

Physics

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Scientific paper

A considerable fraction of dwarf galaxies may represent fossils of the very first star formation in the universe. If true, in much the same way as paleontologists reconstruct the prehistoric life from the fossils, it is possible to reconstruct the general feature of the star formation history at high redshift. Until quite recently, it has been believed that almost all dwarf spheroidal galaxies in the Local group had experienced a sharp decline in the SFR about 10 Gyr ago. This may not be true, however, as latest spectra of individual stars in Draco, Ursa Minor, and Sextans taken by Keck indicate a clear drop of [/Fe] ratio at [Fe/H]=-2, which can be explained only if star formation lasted in these galaxies longer than a few Gyr with SFR much lower than that in the solar neighbourhood disc (~1/20). We have analysed the HST photometric data of 26 fields of 18 dwarf galaxies in the Local group to find that a wide variety of colour-magnitude diagrams of dwarf galaxies is simply explained by a different combination of duration of initial star formation and SFR. Massive dwarf galaxies have higher SFRs (1/10--1/2 of the solar neighbourhood) than less massive ones (~1/20). Galaxies at longer distances from the host galaxy (MW/M31) harbour more extended initial star formation, which implies environmental effects on the fate of gas in dwarf galaxies. These new findings imply much lower star forming activity in the young universe.

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