Spitzer’s View of Galaxies in the High-Redshift Universe
One of the most important observations made by the Spitzer Space Telescope has been the detection of luminous galaxies back to the era of reionization (z ~ 8), when the universe was less than 700 million years old. The key advance made by Spitzer imaging isthe ability, for the first time, to sample the redshifted rest-frame visible light of these galaxies. When combined with broadband multi-wavelength data, Spitzer observations can be fit to stellar population synthesis models to determine the spectral energy distribution of these galaxies and to constrain their stellar masses and ages and their star formation histories. As a result, there is evidence that most of the stellar mass of these galaxies formed at even higher redshifts (z > 10 to 12) and that asignificant number of galaxies should exist in this region.Searches for galaxies at z ~ 9 to 10 continue. Spitzer observations of massive lensing clusters have also played a pivotal role in this study. The first IRAC detection of a z >6 galaxy came from such observations. Since most of these results were obtained with Spitzer/IRAC 3.6/4.5 μm bands, the Spitzer Warm Mission, when combined with future HST/WFC3 observations, will provide a unique opportunity to obtain the first complete census of the assembly of stellar mass as a function of cosmic time back to the era of reionization, yielding unique information on galaxy formation in the early universe.
KeywordsStar Formation Stellar Mass Star Formation Rate Spectral Energy Distribution Star Formation History
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