Testing the paradigm: First spectroscopic evidence of a quasar-galaxy Mpc-scale association at cosmic dawn

Roberto Decarli, Marco Mignoli, Roberto Gilli, Barbara Balmaverde, Marcella Brusa, Nico Cappelluti, Andrea Comastri, Riccardo Nanni, Alessandro Peca, Antonio Pensabene, Eros Vanzella, Cristian Vignali

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


State-of-the-art models of massive black hole formation postulate that quasars at za > a 6 reside in extreme peaks of the cosmic density structure in the early universe. Even so, direct observational evidence of these overdensities is elusive, especially on large scales (≫1 Mpc) as the spectroscopic follow-up of za > a 6 galaxies is observationally expensive. Here we present Keck/DEIMOS optical and IRAM/NOEMA millimeter spectroscopy of a za ∼a 6 Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous za =a 6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a za > a 6 quasar. The Keck observations suggest a za ∼a 6.3 dropout identification of the galaxy. The NOEMA 1.2 mm spectrum shows a 3.5σ line that, if interpreted as [Ca II], would place the galaxy at za =a 6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured [Ca II] luminosity is 3a ×a 108 LaS , in line with expectations for a galaxy with a star formation rate ∼15 MaS yr-1, as inferred from the rest-frame UV photometry. Our combined observations place the galaxy at the same redshift as the quasar, thus strengthening the overdensity scenario for this za > a 6 quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.

Original languageEnglish (US)
Article numberL10
JournalAstronomy and Astrophysics
StatePublished - Nov 1 2019


  • Galaxies: clusters: general
  • Galaxies: high-redshift
  • Quasars: general
  • Quasars: individual: J1030+0524

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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