Millimeter observations of obscured Spitzer 24 μm sources

D. Lutz, L. Yan, L. Armus, G. Helou, L. J. Tacconi, R. Genzel, A. J. Baker

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34 Scopus citations

Abstract

We present MAMBO 1.2 mm observations of 40 extragalactic sources from the Spitzer First Look Survey that are bright in the mid-IR (S24 μm > 1 mJy) but optically obscured (log [vFv(24 μm)/vF v(0.7 μm)] > 1). We use these observations to search for cold dust emission, probing the similarity of their spectral energy distributions to star-forming IR galaxies or obscured AGNs. The sample as a whole is well detected at mean S1.2 mm = 0.74 ± 0.09 mJy and S 1.2 mm/S24 μm = 0.15 ± 0.03. Seven (three) of the sources are individually detected at >3 σ (>5 σ) levels. Mean millimeter fluxes are higher for sources with the reddest mid-IR/optical colors. Optically faint but with relatively low millimeter-to-mid-IR ratios, the typical SEDs are inconsistent with redshifted SED shapes of local star-forming IR galaxies. They also differ from SEDs of typical submillimeter-selected galaxies, with the 24 μm sources that are individually detected by MAMBO possibly representing intermediate objects. Compared to star-forming galaxies, a stronger but optically obscured mid-IR component without associated strong far-IR emission has to be included. This component may be due to luminous optically obscured AGN, which would represent a significant part of the high-redshift AGN population.

Original languageEnglish (US)
Pages (from-to)L13-L16
JournalAstrophysical Journal
Volume632
Issue number1 II
DOIs
StatePublished - Oct 10 2005

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: active
  • Galaxies: starburst
  • Infrared: galaxies

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