Radiation Hydrodynamical Simulations of the First Quasars (1703.00449v2)

Abstract: Supermassive black holes (SMBHs) are the central engines of luminous quasars and are found in most massive galaxies today. But the recent discoveries of ULAS J1120+0641, a $2 \times 10^9$ M${\odot}$ BH at $z =$ 7.1, and ULAS J1342+0928, a $8.0 \times 10^{8}$ M${\odot}$ BH at $z =$ 7.5, now push the era of quasar formation up to just 690 Myr after the Big Bang. Here we report new cosmological simulations of SMBHs with X-rays fully coupled to primordial chemistry and hydrodynamics that show that J1120 and J1342 can form from direct collapse black holes (DCBHs) if their growth is fed by cold, dense accretion streams, like those thought to fuel rapid star formation in some galaxies at later epochs. Our models reproduce all of the observed properties of J1120: its mass, luminosity, and H II region as well as star formation rates and metallicities in its host galaxy. They also reproduce the dynamical mass of the innermost 1.5 kpc of its emission region recently measured by ALMA and J-band magnitudes that are in good agreement with those found by the VISTA Hemisphere Survey.

• The paper demonstrates that direct collapse black holes can grow from ~10⁵ M⊙ to supermassive scales by accreting cold streams at 0.2–0.8 Eddington rates.
• It employs advanced Enzo AMR and MORAY radiation transport simulations to accurately reproduce key quasar properties like mass, luminosity, and H II region extents.
• The simulations also capture merger-triggered star formation and metal enrichment in early quasar hosts, aligning with ALMA and VISTA observational data.

Overview of Radiation Hydrodynamical Simulations of the First Quasars

The paper "Radiation Hydrodynamical Simulations of the First Quasars" presents a comprehensive paper on the formation and evolution of supermassive black holes (SMBHs) in the early universe, conducted through advanced cosmological simulations. The authors, J. Smidt et al., utilize a radiation hydrodynamics model to investigate whether direct collapse black holes (DCBHs) could account for the observed properties of early quasars, specifically ULAS J1120+0641 and ULAS J1342+0928, discovered at redshifts $z = 7.1$ and $z = 7.5$ respectively.

The paper leverages the Enzo adaptive mesh refinement (AMR) cosmology code alongside the MORAY radiation transport module to simulate the environment of nascent SMBHs, including the interrelated gas dynamics, chemistry, and radiation processes. The primary objective is to verify if such quasars can naturally arise from DCBHs by feeding on cold, dense accretion streams, a scenario that contrasts the growth model based on Population III star remnants due to the constraints of their initial conditions and interaction with their environments.

Key Findings

1. Accretion Dynamics: The simulations demonstrate that DCBHs, starting at $\sim 10^5 \, M_\odot$, can grow to the observed masses of SMBHs at $z \sim 7$, assuming sustained feeding by cold accretion flows. Average accretion rates were managed at approximately 0.2 to 0.8 times the Eddington limit, regulated by X-ray feedback from the black holes themselves and supernova feedback from concurrent star formation activities.
2. Reproduced Quasar Properties: The model successfully replicates key observed aspects of ULAS J1120+0641, including its mass, luminosity, and H II region extent. It aligns well with the dynamical mass assessments of the innermost $1.5 \, \text{kpc}$ region derived from ALMA observations and matches the near-infrared luminosity data from VISTA Hemisphere Survey.
3. Star Formation Rates and Metallicity: Given the intense star formation triggered by the merging of host halos and subsequent metal enrichment, the simulations furnish star formation rates and metallicity distributions that mirror observations in high-redshift quasar hosts.

Implications and Future Prospects

The implications of these findings are significant in the context of understanding quasar formation and SMBH growth. The simulations argue for the viability of the DCBH formation pathway under the condition of cold accretion streams, depicting a realistic scenario for high-redshift quasar emergence without necessitating hyper-Eddington accretion rates for the early phases of BH growth.

Theoretical perspectives are offered on the necessity of incorporating evolving spectral emissions of SMBHs to delineate more nuanced interactions within their environments. Moreover, future research directions are proposed, such as evaluating the contributions of metal and dust absorption effects on radiation transport and extending the analysis of varied accretion dynamics and feedback mechanisms in more complex circumnuclear environments.

This paper presents compelling simulation-based evidence towards one of the most debated questions in astrophysical cosmology: how the first SMBHs might have formed under the prevailing conditions of the early universe. By bridging current observational data with a predictive theoretical framework, it initiates fruitful paths for both interpreting upcoming high-redshift quasar observations and refining models of SMBH growth from the inception of cosmic structure formation.