RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 26 February 2015, 11:00-12:00; Duffield Lecture Theatre

Anna Frebel

"The ultra-faint dwarf galaxy Segue 1: Is it a surviving first galaxy?"

The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the oldest, most metal-poor stars are relics from the high-redshift universe, they probe the chemical and dynamical conditions of a time when large galaxies first began to assemble. Recent works have shown that the ultra-faint dwarf galaxies (with L<10^5Lsun) contain a relatively large fraction of extremely metal-poor stars and are devoid of solar-metallicity stars. This reflects a rather short or truncated star formation history similar to what one would expect to occur in a first/early galaxy. Indeed, a spectroscopic study of the faintest dwarf galaxy Segue 1 shows a metallicity range from -4 < [Fe/H] < -1 and abundance patterns like those of other metal-poor halo stars. The over chemical signature of Segue 1 and other ultra-faint dwarfs thus supports the concept that small systems analogous to the surviving ultra-faint galaxies were the building blocks of the Milky Way’s low-metallicity halo. This suggestion is in line with recent age measurments for similar ultra-faint dwarf which showed these galaxies to be single-age stellar systems that are about as old as the universe itself. This opens a new window for studying galaxy formation with the means of stellar chemical analyses.