ALMA confirmation of an obscured hyperluminous radio-loud AGN at z = 6.853 associated with a dusty starburst in the 1.5 deg2 COSMOS field

Ryan Endsley, Daniel P. Stark, Jianwei Lyu, Feige Wang, Jinyi Yang, Xiaohui Fan, Renske Smit, Rychard Bouwens, Kevin Hainline, Sander Schouws

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


We present band 6 ALMA observations of a heavily obscured radio-loud (L1.4 GHz = 1025.4 W Hz−1) active galactic nucleus (AGN) candidate at zphot = 6.83 ± 0.06 found in the 1.5 deg2 COSMOS field. The ALMA data reveal detections of exceptionally strong [C II]158 μm (z[C II] = 6.8532) and underlying dust continuum emission from this object (COS-87259), where the [C II] line luminosity, line width, and 158 μm continuum luminosity are comparable to those seen from z ∼ 7 sub-mm galaxies and quasar hosts. The 158 μm continuum detection suggests a total infrared luminosity of 9 × 1012 L with corresponding very large obscured star formation rate (1300 M yr−1) and dust mass (2 × 109 M). The strong break seen between the VIRCam and IRAC photometry perhaps suggests that COS-87259 is an extremely massive reionization-era galaxy with M ≈ 1.7 × 1011 M. Moreover, the MIPS, PACS, and SPIRE detections imply that this object harbours an AGN that is heavily obscured (τ9.7 μm = 2.3) with a bolometric luminosity of approximately 5 × 1013 L. Such a very high AGN luminosity suggests that this object is powered by an ≈1.6 × 109 M black hole if accreting near the Eddington limit, and is effectively a highly obscured version of an extremely ultraviolet (UV)-luminous (M1450 ≈ −27.3) z ∼ 7 quasar. Notably, these z ∼ 7 quasars are an exceedingly rare population (∼0.001 deg−2), while COS-87259 was identified over a relatively small field. Future very wide area surveys with e.g. Roman and Euclid have the potential to identify many more extremely red yet UV-bright z ≳ 7 objects similar to COS-87259, providing richer insight into the occurrence of intense obscured star formation and supermassive black hole growth among this population.

Original languageEnglish (US)
Pages (from-to)4609-4620
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Apr 1 2023


  • dark ages
  • first stars
  • galaxies: evolution
  • galaxies: high-redshift
  • quasars: supermassive black holes
  • reionization
  • submillimetre: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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