GOODS Spitzer IRAC Observations of High-z Galaxies

The Great Observatory Origins Deep Survey (GOODS) Spitzer Legacy Program has obtained similar to 23.2 hours of TRAC observations in the HDF-N and the CDF-S (similar to 330 arcmin(2) in total), among which a sub-area of 50 arcmin(2) in the HDF-N has been observed to a depth of similar to 72 hours. Utilizing these deep IRAC data, we study the stellar masses and star formation histories of galaxies at z approximate to 6. While some of the i-band dropouts selected by the GOODS ACS observations are detected by these IRAC observations, some of them are not. We find that the i(775)-dropouts in the TRAC-detected sample typically have stellar masses of similar to 10(10)M(circle dot) and ages of a few hundred million years old, consistent with our earlier results based on a smaller sample in the HUDF. On the other hand, the i-dropouts in the IRAC-invisible sample are significantly younger and less massive. Using these results, we derive the lower limit of the global stellar density at z approximate to 6, and find that at least 0.2-1.1% of the stellar mass in our local universe has been locked in stars by z approximate to 6. http://authors.library.caltech.edu/19213/1/Yan2008p8804Second_Annual_Spitzer_Science_Center_Conference_Infrared_Diagnostics_Of_Galaxy_Evolution.pdf