Other
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20253i&link_type=abstract
Spitzer Proposal ID #20253
Other
Scientific paper
We propose deep MIPS 24 micron imaging of galaxies near the z=2.39 radio galaxy 53W002. Recently, we have uncovered an unusually large number of very red galaxies with J-K > 2.7 mag in this field. This is the expected color for old, passively evolving galaxies near the same redshift as the radio galaxy. Our Keck spectroscopic data identify several galaxies near this redshift, including one of red ones. Evidently we are seeing a proto-cluster of galaxies formed at high redshift in an overdense region. Our Spitzer IRAC observations of the red galaxies show that their spectral energy distributions can be fit by old (>1 Gyr), early-type galaxies. According to hierarchical galaxy formation models, the formation of massive cluster galaxies occurs around z ~ 2 - 3, preceding the formation epoch of early-types in low density environment. Finding massive galaxies in an already evolved stage would challenge the hierarchical galaxy formation scenario. However, there is an alternate explanation for the observed SEDs: very dusty young galaxies, where the dust entirely hides the young stars. This scenario would support the hierarchical model. In order to answer the critical question of whether these red galaxies are old (zf > 4) or are dusty, we will obtain a deep 24 micron image of the field. If dust is not seen, it will rule out hidden star formation and pose a severe challenge to the hierarchical model. Our observation will also provide limits or measurements of the IR flux of other z ~ 2.4 galaxies in the field, such as submm galaxies and Lyman-alpha emitters, offering us a more complete view of the star formation history in an overdense region.
Choi Philip
Colbert James
Fadda Dario
Fazio Giovanni
Im Myungshin
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