The Most Distant Quasar and its Host Galaxy

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Distant quasars are unique tracers to study the formation of the earliest supermassive black holes (SMBHs) and the history of cosmic reionization. Despite extensive efforts, only two quasars have been found at z ≥ 7.5, due to a combination of their low spatial density and the high contamination rate in quasar selection. Wang et al. report the discovery of a luminous quasar at z = 7.642, J0313-1806, the most distant quasar yet known. This quasar has a bolometric luminosity of 3.6 × 1013L⊙. Deep spectroscopic observations reveal a SMBH with a mass of (1.6 ± 0.4) × 109 M⊙ in this quasar. The existence of such a massive SMBH just ∼670 million years after the Big Bang challenges significantly theoretical models of SMBH growth. In addition, the quasar spectrum exhibits strong broad absorption line (BAL) features in C IV and Si IV, with a maximum velocity close to 20% of the speed of light. The relativistic BAL features, combined with a strongly blueshifted C IV emission line, indicate that there is a strong active galactic nucleus (AGN)-driven outflow in this system. Atacama Large Millimeter/submillimeter Array (ALMA) observations detect the dust continuum and [C II] emission from the quasar host galaxy, yielding an accurate redshift of 7.6423 ± 0.0013 and suggesting that the quasar is hosted by an intensely star-forming galaxy, with a star formation rate of ∼200 M⊙ yr-1 and a dust mass of ∼7 × 107 M⊙. These observations present the most extreme example of coeval formation of a black hole and galaxy in the very early Universe. Follow-up observations of this reionization-era BAL quasar will provide a powerful probe of the effects of AGN feedback on the growth of the earliest massive galaxies.

Figure caption: ALMA observations of the dust continuum and [C II] line. [Left] The dust continuum map with contour levels of [3, 5, 7, 9, 11, 13] × 0.02 mJy. [Middle] The integrated [C ii] emission with contour levels of [3, 4] × 0.04 Jy km s−1. The sizes of the continuum cutout and the [C II] cutout are 4'' × 4''. The white crosses in the left and middle panels highlight the quasar position derived from VISTA Hemisphere Survey infrared images. [Right] The [C II] spectrum (black) and noise vector (blue) extracted from the data cube with an aperture diameter of 15 centered at the peak position of the continuum map. The spectral fitting (red line) gives FWHM = 312 ± 94 km s−1 and z[CII] = 7.6423 ± 0.0013.

Publication: Feige Wang (University of Arizona) et al., A Luminous Quasar at Redshift 7.642, Astrophysical Journal Letters 907, L1 (20 January 2021).

NRAO Press Release: Quasar Discovery Sets New Distance Record

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