Far-infrared and molecular co emission from the host galaxies of faint quasars at z ∼ 6

Ran Wang, Jeff Wagg, Chris L. Carilli, Roberto Neri, Fabian Walter, Alain Omont, Dominik A. Riechers, Frank Bertoldi, Karl M. Menten, Pierre Cox, Michael A. Strauss, Xiaohui Fan, Linhua Jiang

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99 Scopus citations


We present new millimeter and radio observations of nine z ∼ 6 quasars discovered in deep optical and near-infrared surveys. We observed the 250GHz continuum in eight of the nine objects and detected three of them. New 1.4GHz radio continuum data have been obtained for four sources, and one has been detected. We searched for molecular CO (6-5) line emission in the three 250GHz detections and detected two of them. Combined with previous millimeter and radio observations, we study the far-infrared (FIR) and radio emission and quasar-host galaxy evolution with a sample of 18 z ∼ 6 quasars that are faint at UV and optical wavelengths (rest-frame 1450 magnitudes of m 1450 ≥ 20.2). The average FIR-to-active galactic nucleus (AGN) UV luminosity ratio of this faint quasar sample is about two times higher than that of the bright quasars at z ∼ 6 (m 1450 < 20.2). A fit to the average FIR and AGN bolometric luminosities of both the UV/optically faint and bright z ∼ 6 quasars, and the average luminosities of samples of submillimeter/millimeter-observed quasars at z ∼ 2-5, yields a relationship of L FIR L bol 0.62. Five of the 18 faint z ∼ 6 quasars have been detected at 250GHz. These 250GHz detections, as well as most of the millimeter-detected optically bright z ∼ 6 quasars, follow a shallower trend of ∼ L FIR L bol 0.45 defined by the starburst-AGN systems in local and high-z universe. The millimeter continuum detections in the five objects and molecular CO detections in three of them reveal a few × 108 M of FIR-emitting warm dust and 1010 M of molecular gas in the quasar host galaxies. All these results argue for massive star formation in the quasar host galaxies, with estimated star formation rates of a few hundred M yr-1. Additionally, the higher FIR-to-AGN luminosity ratio found in these 250GHz detected faint quasars also suggests a higher ratio between star formation rate and supermassive black hole accretion rate than the UV/optically most luminous quasars at z ∼ 6.

Original languageEnglish (US)
Article number101
JournalAstronomical Journal
Issue number4
StatePublished - Oct 2011

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • galaxies: active
  • galaxies: high-redshift
  • galaxies: starburst
  • molecular data
  • quasars: general


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