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M. Im (Seoul National University), IRAC GTO Team
We have obtained a deep IRAC image of a cluster of galaxies candidate at z=2.4. This cluster of galaxies candidate is located in the vicinity of a known z=2.4 radio galaxy, 53W002. Our recent NIR observation from the ground reveals that this field contains an unusually large number of J -K > 2.7 galaxies, also known as Hyper Extremely Red Objects (HEROs). In order to tell if HEROs are red galaxies at around z=2.4, or z=12 Lyman break galaxies, we extend their SEDs out to 8 microns using the Spitzer data. We find that the majority of HEROs have SEDs consistent with red galaxies at z = 2.4 rather than z=12 Lyman galaxies, with one possible exception. Our result lends a strong support to the previous claims that there is an overdensity of galaxies at z=2.4 in this field. Furthermore, the discovery of z=2.4 old galaxies suggests that the star formation in cluster of group of galaxies starts early (z > 3).
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Bulletin of the American Astronomical Society, 36 #2
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