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Redshifts from Spitzer Spectra for Optically Faint Radio-selected Infrared Sources
The Astrophysical Journal (2006)
  • D. W. Weedman, Cornell University
  • E. Le Floc'h, University of Arizona
  • Sarah J.U. Higdon, Cornell University
  • J. L. Higdon, Cornell University
  • J. R. Houck, Cornell University
Spectra have been obtained with the Infrared Spectrograph on the Spitzer Space Telescope for 18 optically faint sources (R k23:9 mag) having f(24 m) > 1:0 mJy and having radio detections at 20 cm to a limit of 115 Jy. The sources are within the Spitzer First Look Survey. Redshifts are determined for 14 sources from strong silicate absorption features (12 sources) or strong PAH emission features (two sources), with median redshift of 2.1. Results confirm that optically faint sources of 1 mJy at 24 m are typically at redshifts z  2, verifying the high efficiency in selecting high-redshift sources based on extreme infrared-to-optical flux ratio, and indicate that 24 m sources that also have radio counterparts are not systematically different than samples chosen only by their infrared-tooptical flux ratios. Using the parameter q ¼ log ½ f(24 m)/f(20 cm), 17 of the 18 sources observed have values of 0 < q < 1, in the range expected for starburst-powered sources, but only a few of these show strong PAH emission as expected from starbursts, with the remaindershowing absorbed or power-law spectra consistent with an AGN luminosity source. This confirms previous indications that optically faint Spitzer sources with f(24 m)k 1:0 mJy are predominately AGNs and represent the upper end of the luminosity function of dusty sources at z  2. Based on the characteristics of the sources observed so far, we predict that the nature of sources selected at 24 m will change for f(24 m)P0:5 mJy to sources dominated primarily by starbursts.
  • Dust,
  • Extinction,
  • Galaxies,
  • Active,
  • High-redshift,
  • Starburst,
  • Infrared,
  • Radio Continuum,
  • X-rays
Publication Date
February 20, 2006
Publisher Statement
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Citation Information
D. W. Weedman, E. Le Floc'h, Sarah J.U. Higdon, J. L. Higdon, et al.. "Redshifts from Spitzer Spectra for Optically Faint Radio-selected Infrared Sources" The Astrophysical Journal Vol. 638 Iss. 2 (2006) p. 613 - 621
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