Physics – Optics
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20466s&link_type=abstract
Spitzer Proposal ID #20466
Physics
Optics
Scientific paper
There is persuasive evidence that powerful radio sources are signposts for strongly overdense regions in the early universe. It is in such regions that the processes of galaxy formation and evolution are expected to have proceeded most rapidly, and thus in which we will find the earliest massive galaxies to have formed in the universe. We have been identifying and determining morphologies for galaxies comprising essentially pure old stellar populations at redshifts of 1.5 and 2.5, with the surprising result that, for the three of these galaxies for which we have been able to obtain high-resolution images from adaptive-optics imaging, all are dominated by massive disks of old stars. In two of these, any bulge component accounts for <10% of the total light (and baryonic mass, since all of the stars in both components are old). The presence of these massive (~ 2 to 3 X 10^11 solar masses) disk galaxies at z~2.5 comprising stars that have ages of 1 to 2 Gyr, with no detectible contamination from younger stars, suggests that it would be worthwhile to search for their precursors at higher redshifts. The next optimum redshift range for such a search is z~3.8, for which one obtains maximum discrimation of the 4000 A break in the H-K color. It is necessary to obtain good photometry at longer wavelengths, not only to distinguish between old stellar populations and heavily reddened starbursts, but also to get a good hold on the slope of the spectral-energy distribution at long wavelengths in order to verify an old stellar population in the presence of small amounts of contamination by young stars, which are almost inevitable at these early epochs. We are proposing deep IRAC imaging in all 4 bands of all 7 fields from the Texas Radio Survey with 3.65 < z < 4.05 and extinction A_B < 0.3. Together with ground- based imaging in 4 shorter-wavelength bands, these observations will allow a complete photometric identification and characterization of L* and brighter galaxies associated with these radio sources.
Canalizo Gabriela
McGrath Elizabeth
Stockton Alan
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