Mathematics – Logic
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341814m&link_type=abstract
American Astronomical Society, AAS Meeting #213, #418.14; Bulletin of the American Astronomical Society, Vol. 41, p.232
Mathematics
Logic
Scientific paper
Observational studies of "passive,” or "quiescent” galaxies at high redshift have provided evidence that at least some massive galaxies (>1011 Msun) assembled a majority of their mass at very early times. High-resolution imaging of these galaxies yields a variety of sizes and morphologies, including exponential disks, deVaucouleurs ellipticals, and objects lying somewhere in between. At higher redshifts, there is evidence that quiescent galaxies are extraordinarily compact. Very few of these galaxies resemble the typically large spheroids that dominate galaxies comprising old stellar populations at the present epoch. However, the range in size and morphology 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. With this in mind, we present results from our Spitzer IRAC imaging and Keck DEIMOS spectroscopy of a sample of passive galaxies at z 1.5. The IRAC photometry data are largely immune to the effects of dust. When combined with the DEIMOS spectra as well as HST and ground-based photometry, they place important constraints on the age of the last major epoch of star formation and the amount of recent or ongoing star formation in these galaxies. By exploiting a unique feature in the rest-frame near-IR spectral energy distribution of Gyr-old stellar populations, we are able to separate the effects of age and metallicity in the spectral synthesis modeling of these galaxies. We use these improved age and metallicity estimates in conjunction with high-resolution morphological data in order to discuss plausible formation mechanisms and place them in the context of current models of galaxy formation.
Support for this work was provided by NASA through a Spitzer Space Telescope award issued by JPL/Caltech.
McGrath Elizabeth J.
Stockton Alan
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