An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30 (1502.07418v2)

Abstract: So far, roughly 40 quasars with redshifts greater than z=6 have been discovered. Each quasar contains a black hole with a mass of about one billion solar masses ($10^9 M_\odot$). The existence of such black holes when the Universe was less than 1 billion years old presents substantial challenges to theories of the formation and growth of black holes and the coevolution of black holes and galaxies. Here we report the discovery of an ultra-luminous quasar, SDSS J010013.02+280225.8, at redshift z=6.30. It has an optical and near-infrared luminosity a few times greater than those of previously known z>6 quasars. On the basis of the deep absorption trough on the blue side of the Ly $\alpha$ emission line in the spectrum, we estimate the proper size of the ionized proximity zone associated with the quasar to be 26 million light years, larger than found with other z>6.1 quasars with lower luminosities. We estimate (on the basis of a near-infrared spectrum) that the black hole has a mass of $\sim 1.2 \times 10^{10} M_\odot$, which is consistent with the $1.3 \times 10^{10} M_\odot$ derived by assuming an Eddington-limited accretion rate.

• The paper identifies a quasar at z=6.30 harboring a 1.24×10^10 M☉ black hole, marking the most luminous quasar known at these redshifts.
• The study combines optical and infrared surveys with spectroscopic verification, employing virial methods to estimate mass and luminosity.
• The discovery challenges current models of rapid black hole growth and provides new insights into accretion mechanisms and cosmic reionization.

Essay on 'An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30'

The paper documents the discovery of an exceedingly luminous quasar, SDSS J010013.02+280225.8 (hereafter J0100+2802), at a redshift $z = 6.30$. This quasar harbors a remarkably massive black hole with an estimated mass of approximately $1.2 \times 10^{10} M_\odot$. The implications of this find are manifold and intricate, posing significant questions to existing models of black hole formation and growth in the early universe.

Overview and Methodology

The identification of J0100+2802 was achieved through a combination of optical and infrared photometric data captured from several sky surveys including the Sloan Digital Sky Survey (SDSS), the Two Micron All Sky Survey (2MASS), and the Wide-field Infrared Survey Explorer (WISE). The researchers employed color-selection methods unique to high-redshift quasars, relying on the red optical color and photometric redshift estimates that corresponded to high $z$ values.

The quasar's redshift was later verified with optical spectroscopy from facilities like the Lijiang 2.4-m telescope and the Large Binocular Telescope. These spectra revealed a distinct Gunn-Peterson absorption trough and high-level ionization near the Ly$\alpha$ emission line. The large ionized proximity zone, quantified at 26 million light years, underscores its immense luminosity.

The evaluation of the black hole mass was based on the Mg II and optical/infrared continuum luminosities, employing virial black hole mass estimation techniques that derive mass from emission line widths and continuum luminosities. Such analyses estimated the black hole mass to be $1.24 \times 10^{10} M_\odot$ under Eddington luminescence conditions.

Key Findings

The significance of J0100+2802's discovery is partly embedded in its bolometric luminosity and enormous black hole mass, positioning it as the most luminous known quasar at $z>6$. The mass and energetic output far exceed previously identified quasars at similar redshifts — for example, the $z=7.085$ quasar ULAS J1120+0641 — indicating a rapid accretion period that challenges prevalent theories regarding the mass assembly timelines of supermassive black holes and their host galaxies.

Additionally, the paper suggests J0100+2802 as a weak-line quasar (WLQ) due to its narrow Ly$\alpha$+NV emission line equivalent width. This property may bear implications for our understanding of star formation and accretion processes during these epochs, given that WLQs often show active star formation.

Implications and Future Directions

The quasar's existence introduces challenging questions for cosmological models, specifically regarding the mechanisms that enable rapid black hole growth during the nascent epochs post-Big Bang, suggesting possible super-Eddington accretion rates or frequent merging events. The presence of such massive black holes may also suggest the early decoupling of the black hole growth from the development of host galaxies.

For future research, J0100+2802 provides a fertile investigative domain, particularly through (sub)millimeter observations to explore star-formation activities and gas dynamics in the vicinity of massive black holes. Moreover, its large proximity zone offers a unique opportunity to probe the intergalactic medium's ionization state during the era of cosmic reionization.

In summation, the discovery of J0100+2802 serves as a critical datum point to refine models of early-universe supermassive black hole growth and their relationship with host galactic environments. As additional high-redshift quasars are uncovered, these findings will continue to reshape and deepen our understanding of the universe's formative epochs.