A Luminous Quasar at Redshift 7.642 (2101.03179v1)

Abstract: 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 $z\ge7.5$, due to a combination of their low spatial density and the high contamination rate in quasar selection. We 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 $3.6\times10^{13} L_\odot$. Deep spectroscopic observations reveal a SMBH with a mass of $(1.6\pm0.4) \times10^9M_\odot$ in this quasar. The existence of such a massive SMBH just $\sim$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 CIV and SiIV, with a maximum velocity close to 20% of the speed of light. The relativistic BAL features, combined with a strongly blueshifted CIV emission line, indicate that there is a strong active galactic nucleus (AGN) driven outflow in this system. ALMA observations detect the dust continuum and [CII] emission from the quasar host galaxy, yielding an accurate redshift of $7.6423 \pm 0.0013$ and suggesting that the quasar is hosted by an intensely star-forming galaxy, with a star formation rate of $\rm\sim 200 ~M_\odot ~yr^{-1}$ and a dust mass of $\sim7\times10^7~M_\odot$. Followup 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.

• The paper reports the discovery of J0313-1806, the most distant luminous quasar hosting a ~1.6×10^9 M☉ black hole in the early universe.
• It utilizes spectroscopic and ALMA observations to reveal high-velocity AGN winds and vigorous star formation in its host galaxy.
• The study challenges existing models of SMBH formation and underscores the need for advanced simulations and higher-resolution follow-ups.

A Luminous Quasar at Redshift 7.642

The discovery of the luminous quasar J0313-1806 at redshift $z = 7.642$ presents a notable advancement in the field of high-redshift astrophysics, offering significant implications for our understanding of early cosmic history and supermassive black hole (SMBH) formation. This essay provides an expert overview, analyzing the principal findings, implications, and speculative future research directions suggested by the analysis conducted by Wang et al.

The primary significance of the discovery of J0313-1806 lies in its extreme redshift, making it the most distant quasar identified at the time of the paper, existing merely 670 million years after the Big Bang. This quasar hosts a SMBH with an estimated mass of $(1.6 \pm 0.4) \times 10^9 M_\odot$, challenging existing theoretical models of SMBH formation, which have yet to account fully for such rapid early growth. The inferred SMBH mass and Eddington ratio $L_{\rm bol}/L_{\rm Edd} = 0.67 \pm 0.14$ indicate an active growth phase, compelling a reexamination of models related to black hole seeds and their early cosmological development, favoring scenarios like direct-collapse black holes which can produce larger initial seeds in the range of $10^4 - 10^5 M_\odot$.

Spectroscopic observations reveal broad absorption lines, indicating the presence of powerful outflows with relativistic speeds up to 20% the speed of light. Observation of such high-velocity outflows, uncommon at lower redshifts, suggests potential evolutionary trends in quasar feedback mechanisms. The strong blueshift of the \ion{C}{4} emission line further corroborates the presence of AGN-driven winds, a critical process in regulating accretion and possibly affecting star formation within the host galaxy.

The ALMA observations of J0313-1806 present additional insights, identifying intense star-forming activity in the quasar's host galaxy, indicating a star formation rate of approximately $200 ~M_\odot ~{\rm yr^{-1}}$ and significant dust content ($\sim 7 \times 10^7~M_\odot$). These properties emphasize a scenario where SMBH and host galaxy growth are closely coupled, highlighting the relevance of intense, early star formation processes in shaping the host galaxies of early-universe quasars.

The theoretical and empirical analysis presented in this paper challenges current cosmological models, demanding more nuanced formations of black hole growth dynamics. The observations suggest a diversity of evolutionary paths that early-universe active galaxies might undertake, influenced significantly by feedback mechanisms.

Future research is poised to address the limitations in observing such high redshift quasars and focus on improving methodologies to quantify SMBH masses with confidence, possibly through space-based platforms like JWST, which will allow for higher resolution follow-ups in the rest-frame near-infrared wavelengths. Furthermore, advanced simulations that incorporate both baryonic physics and feedback processes will be essential for expanding our understanding of SMBH growth and the apparent abundance of massive black holes in the early universe.

The discovery of J0313-1806 thus serves as a critical observational link, shedding light on the epoch of reionization and providing a robust experimental footing for theories on SMBH and galactic evolution during these formative cosmic stages.