Spectral energy distributions of type 2 quasi-stellar objects: Obscured star formation at high redshifts

D. Rigopoulou, V. Mainieri, O. Almaini, A. Alonso-Herrero, J. S. Huang, G. Hasinger, G. Rieke, J. Dunlop, I. Lehmann

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


We present new mid-infrared and submillimetre observations for a sample of eight high-redshift type 2 quasi-stellar objects (QSOs) located in the Chandra Deep Field-South. The sources are X-ray absorbed with luminosities in excess of 1044 erg s-1. Two of the targets have robust detections, S/N > 4, while further three targets are marginally detected with S/N ≥ 2.5. All sources are detected in multiple mid-infrared bands with the Spitzer Space Telescope. The multiwavelength spectral energy distributions (SEDs) of the type 2 QSOs are compared to those of two local ultraluminous galaxies (Arp220 and IR22491) in order to assess contributions from a star-forming component in various parts of the SED. We suggest that their submm emission is possibly due to a starburst while a large fraction of the mid-infrared energy is likely to originate in the obscured central quasar. Using the mid-infrared and submm observations, we derive infrared luminosities which are found to be in excess of L > 1012 L. The submm (850 μm) to X-ray (2 keV) spectral indices (αSX) span a wide range. About half of the type 2 QSOs have values typical for a Compton-thick active galactic nuclei with only 1 per cent of the nuclear emission seen through scattering, and the remaining with values typical of submm-bright galaxies. Combining the available observational evidence, we outline a possible scenario for the early stages of evolution of these sources.

Original languageEnglish (US)
Pages (from-to)1199-1207
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Dec 2009


  • Galaxies: active
  • Galaxies: nuclei
  • Quasars: general
  • Submillimetre

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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