The High Redshift Universe Next Door
Thu, March 31, 2016
The dwarf galaxies around the Milky Way are extremely valuable laboratories for studying the nature of dark matter, the threshold for galaxy formation, and chemical evolution in the early universe. After reviewing the revolution in our understanding of the Milky Way’s satellite population that has resulted from recent wide-field surveys, I will discuss how these objects provide unique new windows into processes that occurred at high redshift and can usually only be studied in the distant universe. Spectroscopy at both low and high resolution shows that a significant fraction of the stars in the least luminous galaxies are extremely metal-poor, with [Fe/H] < -3. I will describe spectroscopy using the Magellan telescopes of metal-poor stars in Milky Way satellites spanning a factor of 10^4 in luminosity. For many elements the chemical abundance patterns of extremely metal-poor stars appear nearly identical in all galaxies, implying universal early chemical evolution. However, larger samples of dwarf galaxy stars are now revealing peculiarities that trace individual nucleosynthesis events, offering insight into the first generations of stars that formed in our nearest galactic neighbors.