Spitzer mid-infrared spectroscopy of 70 μm-selected distant luminous infrared galaxies

Kate Brand, Dan W. Weedman, Vandana Desai, Emeric Le Floc'h, Lee Armus, Arjun Dey, Jim R. Houck, Buell T. Jannuzi, Howard A. Smith, B. T. Soifer

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


We present mid-infrared spectroscopy obtained with the Spitzer Space Telescope of a sample of 11 optically faint, infrared luminous galaxies selected from a Spitzer MIPS 70 μm imaging survey of the NDWFS Bootes field. These are the first Spitzer IRS spectra presented of distant 70 μm-selected sources. All the galaxies lie at redshifts 0.3 < z < 1.3 and have very large infrared luminosities of LIR ∼ (0.1-17) × 10 12 Z. Seven of the galaxies exhibit strong emission features attributed to polycyclic aromatic hydrocarbons (PAHs). The average IRS spectrum of these sources is characteristic of classical starburst galaxies but with much larger infrared luminosities. The PAH luminosities of vL v(7.7 μm) ∼ (0.4-7) × 1011 L imply star formation rates of ∼40-720 M yr-1. Four of the galaxies show deep 9.7 μm silicate absorption features and no significant PAH emission features (6.2 μm equivalent widths <0.03 μm). The large infrared luminosities and low vfv(70 μm)/vf v(24 μm) flux density ratios suggests that these sources have AGNs as the dominant origin of their large mid-infrared luminosities, although deeply embedded but luminous star-bursts cannot be ruled out. If the absorbed sources are AGN-dominated, a significant fraction of all far-infrared bright, optically faint sources may be dominated by AGNs.

Original languageEnglish (US)
Pages (from-to)119-127
Number of pages9
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 20 2008


  • Galaxies: active
  • Galaxies: starburst
  • Infrared: galaxies
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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