Panoramic High Resolution Spectroscopy

Stellar populations in galaxies are vast repositories of fossil information. In recent years it has become possible to consider high resolution spectroscopic surveys of millions of stars. New high resolution multi-object spectrographs on 4-8m class telescopes (HERMES, WFMOS) will allow us for the first time to make large and detailed chemical abundance surveys of stars in the Galactic disk, bulge and halo, and apply the techniques of chemical tagging to recovering the fossil information left over from galaxy assembly. These instruments will have strong synergies with the GAIA astrometric satellite due to launch in 2011. The level of detail made possible by these future facilities will be necessary if we are to fully understand the physical processes involved in galaxy formation. 1. WFMOS and Galactic Archaeology WFMOS is a proposed large wide-field multi-object fiber spectrometer to go at the prime focus of Subaru in a collaborative arrangement between Subaru and Gemini. WFMOS has high and low resolution modes, and is the top-priority next-generation instrument for Gemini. The high resolution spectrometer of WFMOS will have a resolution of about R = 40, 000, fed by about 1000 fibers. We can hope for a SNR of about 100 per resolution element for stars of V = 17 in a 4-hour exposure. Why would one want a high resolution multi-object spectrometer ? Galactic archaeology is the primary science driver. The goals of galactic archaeology are to seek signatures or fossils from the epoch of Galaxy formation, to give us insight into the processes which took place as the Galaxy formed. Specifically, we aim to reconstruct the star-forming aggregates that built up the disk, halo and bulge of our Galaxy. For some of these aggregates, their debris can be recognised kinematically as stellar moving groups. For others, the dynamical information was lost through disk heating processes during the formation and evolution of the disk, but they are still recognizable by their chemical signatures; ie by their detailed distributions of abundances of many different chemical elements. As an example of reconstructing such ancient star-forming aggregates, we can start with the galactic halo. The halo is a slowly rotating spheroidal component of metal-poor stars, and is believed to be built up at least partly by accretion of small metal-poor satellite galaxies. Most halo building events occurred long ago, but some are still ongoing and sometimes directly visible: the Sgr dwarf is a well-known example of an ongoing halo accretion event. The halo represents