Program: GN-2010A-Q-68

One of the great mysteries in contemporary extragalactic astronomy is the nature and fate of the the very compact massive galaxies with old stellar populations recently found at z > 2. Essentially all early-type galaxies at very high redshifts fall into this class, but such galaxies are extremely rare in the Universe today. It remains quite unclear how these galaxies, which seem to account for at least 15% of the oldest stars in the Universe, have been integrated into present-day galaxies. They are too faint be studied in any detail (e.g., spectroscopically) with current facilities. A key to gaining some physical understanding of them is to find examples of the very few that may have survived, more-or-less intact, to lower redshifts. From a region comprising ~1100 square degrees of sky, we have isolated a sample of 30 objects that have a reasonable probablility of being similar to these compact high-redshift galaxies. Our objects have initially been selected from the area common to the Sloan Digital Sky Survey DR7 (SDSS) and the UKIRT Infrared Sky Survey DR6plus (UKIDSS). The search criteria included both photometric constraints to match the spectral-energy distributions (SEDs) expected for old stellar populations at a range of redshifts from 0.4 to 0.8, quantized in steps of 0.05 in z, and compactness constraints that picked out only objects that were essentially stellar. We have further sifted this list by using additional constraints to eliminate certain varieties of carbon stars, which would otherwise be significant contaminants of the sample, and by running the photometric data through Hyper-z, to eliminate objects that would be marginal fits to old stellar population SEDs, given the specific photometric errors for each object. We have considerable confidence that most of our reduced sample of 30 comprises galaxies of the type we are searching for, but we need to confirm redshifts before carrying out more detailed investigations. We are therefore proposing a GMOS spectroscopy program to this end. The program can be done in marginal conditions with respect to seeing and can tolerate thin cloud cover.