Photometric redshifts in the IRAC shallow survey

M. Brodwin, M. J.I. Brown, M. L.N. Ashby, C. Bian, K. Brand, A. Dey, P. R. Eisenhardt, D. J. Eisenstein, A. H. Gonzalez, J. S. Huang, B. T. Jannuzi, C. S. Kochanek, E. McKenzie, S. S. Murray, M. A. Pahre, H. A. Smith, B. T. Soifer, S. A. Stanford, D. Stern, R. J. Elston

Research output: Contribution to journalArticle

117 Scopus citations


Accurate photometric redshifts are calculated for nearly 200,000 galaxies to a 4.5 μm flux limit of ∼13 μJy in the 8.5 deg2 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 〈z〉 = 1.24, ISCS J1434.5+3427. Finally, we present a measurement of the 4.5 μm-selected galaxy redshift distribution.

Original languageEnglish (US)
Pages (from-to)791-803
Number of pages13
JournalAstrophysical Journal
Issue number2 I
StatePublished - Nov 10 2006
Externally publishedYes


  • Galaxies: clusters: general
  • Galaxies: distances and redshifts
  • Galaxies: evolution
  • Galaxies: photometry
  • Methods: statistical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Brodwin, M., Brown, M. J. I., Ashby, M. L. N., Bian, C., Brand, K., Dey, A., Eisenhardt, P. R., Eisenstein, D. J., Gonzalez, A. H., Huang, J. S., Jannuzi, B. T., Kochanek, C. S., McKenzie, E., Murray, S. S., Pahre, M. A., Smith, H. A., Soifer, B. T., Stanford, S. A., Stern, D., & Elston, R. J. (2006). Photometric redshifts in the IRAC shallow survey. Astrophysical Journal, 651(2 I), 791-803.