No Evidence for Enhanced [O iii] 88 μm Emission in a z ∼ 6 Quasar Compared to Its Companion Starbursting Galaxy

Fabian Walter, Dominik Riechers, Mladen Novak, Roberto Decarli, Carl Ferkinhoff, Bram Venemans, Eduardo Bañados, Frank Bertoldi, Chris Carilli, Xiaohui Fan, Emanuele Farina, Chiara Mazzucchelli, Marcel Neeleman, Hans Walter Rix, Michael A. Strauss, Bade Uzgil, Ran Wang

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We present Atacama Large Millimeter/submillimeter Array band 8 observations of the [O iii] 88 μm line and the underlying thermal infrared continuum emission in the z = 6.08 quasar CFHQS J2100-1715 and its dust-obscured starburst companion galaxy (projected distance: ∼60 kpc). Each galaxy hosts dust-obscured star formation at rates >100 M o yr-1, but only the quasar shows evidence for an accreting 109 M o black hole. Therefore we can compare the properties of the interstellar medium in distinct galactic environments in two physically associated objects, ∼1 Gyr after the big bang. Bright [O iii] 88 μm emission from ionized gas is detected in both systems; the positions and linewidths are consistent with earlier [C ii] measurements, indicating that both lines trace the same gravitational potential on galactic scales. The [O iii] 88 μm/far-infrared (FIR) luminosity ratios in both sources fall in the upper range observed in local luminous infrared galaxies of similar dust temperature, although the ratio of the quasar is smaller than in the companion. This suggests that gas ionization by the quasar (expected to lead to strong optical [O iii] 5008 Å emission) does not dominantly determine the quasar's FIR [O iii] 88 μm luminosity. Both the inferred number of photons needed for the creation of O++ and the typical line ratios can be accounted for without invoking extreme (top-heavy) stellar initial mass functions in the starbursts of both sources.

Original languageEnglish (US)
Article numberL22
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Dec 20 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • galaxies: ISM
  • galaxies: high-redshift
  • quasars: emission lines
  • quasars: general
  • submillimeter: ISM


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