Old Stellar Populations at High Redshifts

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AST-0307335StocktonSemi-analytic models based on the standard cold dark matter (CDM) theory suggest that most elliptical galaxies formed between redshifts one and two, with the most massive forming most recently. However, there are observations which sit uneasily with this picture. Although some questions can be addressed by careful and detailed examination of local ellipticals, it is nevertheless crucial to have observations of galaxies at high redshifts with populations of stars that were already old at the epoch corresponding to those redshifts (simply called 'old galaxies'). The centerpiece of this project is acquiring images of a significant and representative sample of old galaxies at redshifts between 1.5 and 2.5, and possibly also in the range 3:4 to 3:8, using adaptive optics (AO) on 8-m-class telescopes to deliver resolutions three to four times better than can be obtained with the Hubble Space Telescope. Emphasis is on infra-red imaging, starting with fields for which deep optical data already exist, to yield volume density, clustering properties, and the distribution of morphologies. Identifying and determining physical properties for the most luminous old galaxies over a range of redshifts will place new constraints on theories of their formation and early evolution.Integrated into this proposal are procedures to ensure wide and timely dissemination of the results, both within the scientific community and to interested lay audiences, and the project will provide material for both undergraduate teaching and general public outreach.***