The ∼0.9 mJy sample: A mid-infrared spectroscopic catalog of 150 infrared-luminous, 24 μm selected galaxies at 0.3 ≤ z ≤ 3.5

Kalliopi M. Dasyra, Lin Yan, George Helou, Anna Sajina, Dario Fadda, Michel Zamojski, Lee Armus, Bruce Draine, David Frayer

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37 Scopus citations


We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR) luminous galaxies in the Spitzer extragalactic first look survey obtained with the IR spectrograph on board the Spitzer Space Telescope. The sample is selected to be brighter than ∼0.9 mJy at 24μm and it has a redshift distribution in the range [0.3, 3.5], with a peak at z = 1. It primarily comprises ultraluminous IR galaxies (ULIRGs) at z ≳ 1 and luminous IR galaxies at z < 1, as estimated from their monochromatic rest-frame 14μm luminosities. The number of sources with spectra that are dominated by an active galactic nucleus (AGN) continuum is 49, while 39 sources have strong, star formation related features. For this classification, we used the equivalent width (EW) of the 11.3μm polycyclic aromatic hydrocarbon (PAH) feature. Several intermediate and high z starbursts have higher PAH EW than local ULIRGs, which could be indicative of an elevated star formation activity. Moreover, an increase in the AGN activity is observed with increasing z and luminosity, based on the decreasing EW of PAHs and the increasing [NeIII]/[NeII] ratio. Spectral stacking leads to the detection of weak features such as the 3.3μm PAH, the H2 0-0 S(1) and S(3) lines, and the [NeV] line. We observe differences in the flux ratios of PAHs in the stacked spectra of IR-luminous galaxies with redshift or luminosity, which cannot be attributed to extinction effects since both the depth and the profile of the silicate absorption feature at 9.7μm remain the same at z < 1 and z ≥ 1. When placing the observed galaxies on IR color-color diagrams, we find that the wedge defining AGNs comprises most sources with continuum-dominated spectra, but also contains many starbursts and sources with strong silicate absorption at 9.7μm. The comparison of the 11.3μm PAH EW and the H-band effective radius, measured from Hubble Space Telescope data, indicates that sources with EWs ≥ 2μm, are typically more extended than 3kpc. However, there is no strong correlation between the MIR spectral type and the near-IR extent of the sources.

Original languageEnglish (US)
Pages (from-to)1123-1146
Number of pages24
JournalAstrophysical Journal
Issue number2
StatePublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Dust, extinction
  • Galaxies: Active
  • Galaxies: Evolution
  • Galaxies: Formation
  • Galaxies: High-redshift
  • Galaxies: Interactions
  • Galaxies: Starburst
  • Infrared: Galaxies


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