Measuring Dark Energy with the Wide-Field Multi-Object Spectrograph (WFMOS)

Dark energy is one of the greatest scientific challenges of the 21st century. One of the key questions facing cosmologists is whether dark energy is either a breakdown of General Relativity on large scales or a new form of matter in the Universe with a negative effective pressure. This question can only be answered through a suite of different observations as a function of redshift. In this paper, I briefly review various dark energy reports published in the last year, which all highlight the importance of the baryon acoustic oscillations (BAO) for probing the "dark physics" of the Universe. I also summarize the recent measurements of the BAO in large galaxy redshift surveys. I then look forward to a new instrument planned by the Subaru and Gemini communities called the "Wide-Field Multi-Object Spectrograph" (WFMOS) for the Subaru telescope. The baseline design of this facility includes ~4500 spectroscopic fibers over a field-of-view of 1.5 degree diameter, covering a wavelength range of 0.39 to 1 microns. The instrument is schedule for first-light early next decade and will perform massive spectroscopic surveys of both distant galaxies and faint stars in our own Galaxy. The WFMOS dark energy surveys will deliver ~1% errors on the angular-diameter distance and Hubble parameter to high redshift. WFMOS will also be a unique user-facility allowing astronomers to address a host of astrophysical problems like galaxy evolution, the intergalactic medium and calibrate photometric redshifts. The WFMOS archive will also provide a rich resource for further ancillary science much like the present-day SDSS archive.