Volume 631, November 2019
|Number of page(s)||5|
|Section||Letters to the Editor|
|Published online||13 November 2019|
Letter to the Editor
Testing the paradigm: First spectroscopic evidence of a quasar–galaxy Mpc-scale association at cosmic dawn
INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
2 INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
3 Dipartimento di Fisica e Astronomia, Universitá degli Studi di Bologna, Via P. Gobetti 93/2, 40129 Bologna, Italy
4 Physics Department, University of Miami, Coral Gables, FL 33124, USA
Accepted: 25 October 2019
State-of-the-art models of massive black hole formation postulate that quasars at z > 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 z > 6 galaxies is observationally expensive. Here we present Keck/DEIMOS optical and IRAM/NOEMA millimeter spectroscopy of a z ∼ 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 z = 6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a z > 6 quasar. The Keck observations suggest a z ∼ 6.3 dropout identification of the galaxy. The NOEMA 1.2 mm spectrum shows a 3.5σ line that, if interpreted as [C II], would place the galaxy at z = 6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured [C II] luminosity is 3 × 108 L⊙, in line with expectations for a galaxy with a star formation rate ∼15 M⊙ 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 z > 6 quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.
Key words: quasars: general / quasars: individual: J1030+0524 / galaxies: high-redshift / galaxies: clusters: general
© ESO 2019
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