Physics
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50287m&link_type=abstract
Spitzer Proposal ID #50287
Physics
Scientific paper
There is a growing amount of observational evidence from studies of ?passive galaxies? at high redshift that at least some massive galaxies formed very early in the history of the Universe. These galaxies contain stellar populations that are already >1?2 Gyr old at the observed epoch, with no significant recent star formation. At z~1.5, our HST ACS and NICMOS imaging of seven such galaxies reveals a range of morphologies, including exponential disks, deVaucouleurs ellipticals, and even a possible ?dry merger,? where the apparent lack of gas prevents new episodes of merger-induced star formation from occurring. This range in morphologies indicates that several different mechanisms could be important in building up the most massive galaxies in the Universe. In order to place tighter constraints on galaxy formation scenarios, we need to eliminate any remaining doubts about the nature of the stellar populations in these galaxies. Using Spitzer IRAC and improved population syntheses models, we can finally break the age-metallicity degeneracy that plagues shorter-wavelength observations. Photometry from the 4 IRAC bands will constrain the long-wavelength portion of the spectral energy distributions, yielding important information about the dust and metal content of these galaxies, as well as unprecedented accuracy in the age measurements. Together, this information will help constrain when the first major epoch of star formation occurred, and how the first massive galaxies formed.
McGrath Elizabeth
Stockton Alan
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