paper

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

arXiv:1910.12887 · doi:10.1051/0004-6361/201936813

Abstract

State-of-the-art models of massive black hole formation postulate that quasars at 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 galaxies is observationally expensive. Here we present Keck / DEIMOS optical and IRAM / NOEMA millimeter spectroscopy of a Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous =6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a quasar. The Keck observations suggest a dropout identification of the galaxy. The NOEMA 1.2mm spectrum shows a 3.5 line that, if interpreted as [CII], would place the galaxy at =6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured [CII] luminosity is L, in line with expectations for a galaxy with a star formation rate M yr, 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 quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.

5 pages, 3 figures. Letter accepted for publication in A&A

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