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Published November 10, 2006 | Published
Journal Article Open

Photometric redshifts in the Irac shallow survey


Accurate photometric redshifts are calculated for nearly 200,000 galaxies to a 4.5 μm flux limit of ~13 μJy in the 8.5 deg^2 Spitzer IRAC Shallow Survey. Using a hybrid photometric redshift algorithm incorporating both neural net and template-fitting techniques, calibrated with over 15,000 spectroscopic redshifts, a redshift accuracy of σ = 0.06(1 + z) is achieved for 95% of galaxies at 0 < z < 1.5. The accuracy is σ = 0.12(1 + z) for 95% of active galactic nuclei (AGNs) at 0 < z < 3. Redshift probability functions, central to several ongoing studies of the galaxy population, are computed for the full sample. We demonstrate that these functions accurately represent the true redshift probability density, allowing the calculation of valid confidence intervals for all objects. These probability functions have already been used to successfully identify a population of Spitzer-selected high-redshift (z > 1) galaxy clusters. We present one such spectroscopically confirmed cluster at = 1.24, ISCS J1434.5+3427. Finally, we present a measurement of the 4.5 μm-selected galaxy redshift distribution.

Additional Information

© 2006 The American Astronomical Society. Received 2006 April 26; accepted 2006 July 13. We are grateful and indebted to the teams who built the instruments used in this project. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This paper made use of data from the NOAO Deep Wide-Field Survey (NDWFS), which was supported by NOAO, AURA, Inc., and the National Science Foundation. We thank the entire NDWFS survey team and those who operate and maintain Kitt Peak National Observatory, whose facilities were used to obtain the NDWFS Bootes field images. Spectroscopic redshifts that contributed to the training of our photometric redshift algorithms were obtained by numerous groups. In addition to the vast number of redshifts from the AGES survey described in the text, redshifts were contributed by various projects, including ones led by Hyron Spinrad, Steve Dawson, Richard Green, James Rhoads, Sangeeta Malhotra, and George Djorgovski. We are grateful to them for generously sharing their redshifts with us. We are grateful to the staff of the MMT Observatory, W. M. Keck Observatory, and KPNO for their help with obtaining the various spectroscopic data. A. H. G. and E. M. acknowledge support from an NSF Small Grant for Exploratory Research under award AST 04-36681. S. A. S.'s work was performed under the auspices of the US Department of Energy, National Nuclear Security Administration by the University of California, Lawrence Livermore National Laboratory under contract W-7405-Eng-48.

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