Infrared Space Observatory observations of the 53W002 group at 6.7 microns: In search of the oldest stellar populations at z=2.4

W C Keel, W T Wu, P P van der Werf, R A Windhorst, J S Dunlop, S A Eales, I Waddington, M Holmes

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We present a deep Infrared Space Observatory (ISO) observation at 6.7 mum of the 53W002 group of galaxies and active galactic nuclei (AGNs) at z = 2.4. This approximately samples the emitted K band. Faint, blue star-forming objects are not detected, as expected from their very blue color across the emitted optical and UV spectrum. However, 53W002 itself is detected at the similar to3 sigma level, with an emitted color that is appropriate V - K for a population that formed starting at z = 3.6-7.0 most likely z = 4.7. This fits with shorter wavelength data, suggesting that the more massive members of this group, which may all host AGNs, began star formation earlier in deeper potential wells than the compact Lyalpha emission objects. Two foreground galaxies are detected, as are several stars. One additional 6.7 mum source closely coincides with an optically faint galaxy, potentially at z p. The overall source counts are consistent ( within the errors of such a small sample) with the other ISO deep 2 - 3 fields at 6.7 mum.

Original languageEnglish
Pages (from-to)712-722
Number of pages11
JournalPublications of the Astronomical Society of the Pacific
Issue number822
Publication statusPublished - Aug 2004

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