The Age of Discovery with the James Webb: Excavating the Spectral Signatures of the First Massive Black Holes

Abstract

The James Webb Space Telescope (JWST) will open a new window of the most distant universe and unveil the early growth of supermassive black holes (BHs) in the first galaxies. In preparation for deep JWST imaging surveys, it is crucial to understand the color selection of high-redshift accreting seed BHs. We model the spectral energy distribution of super-Eddington accreting BHs with millions of solar masses in metal-poor galaxies at z 8, applying post-process line transfer calculations to radiation hydrodynamical simulation results. Ten kilosecond exposures with the NIRCam and MIRI broadband filters are sufficient to detect the radiation flux from the seed BHs with bolometric luminosities of L bol 10 45 erg s −1 . While the continuum colors are similar to those of typical low-z quasars, strong Hα line emission with a rest-frame equivalent width EW rest 1300 Å is so prominent that the line flux affects the broad-band colors significantly. The unique colors, for instance F356W−F560W 1 at 7 < z < 8 and F444W−F770W 1 at 9 < z < 12, provide robust criteria for photometric selection of the rapidly growing seed BHs. Moreover, NIRSpec observations of low-ionization emission lines can test whether the BH is fed via a dense accretion disk at super-Eddington rates.

Radiative feedback on supermassive star formation: the massive end of the Population III initial mass function

“…Once the conditions for super-Eddington mass accretion are satisfied, the central BH becomes a milli-QSO radiating with 𝐿 bol 𝐿 Edd 4×10 42 erg s −1 (𝑀 • /3×10 4 M ). While the IMBH in the MMH halo located at 𝑧 ∼ 15 would be too faint to be observed, more luminous milli-QSOs with 𝐿 bol ∼ 10 45 erg s −1 , resulting from higher BH mass 𝑀 • 10 6 M and/or extremely high-Eddington ratios reach the detection limit for upcoming observations by the James Webb Space Telescope (Inayoshi et al 2022a). A future discovery of such milli-QSOs at 𝑧 > 10 will be strong evidence of IMBH formation in the primordial universe and its rapid mass growth to establish SMBH populations found at 𝑧 ∼ 7.…”

How long do high-redshift massive black hole seeds remain outliers in black hole vs. host galaxy relations?

“…The spectra found in Pacucci et al (2015) have a steep slope in the infrared, due to radiation from the DCBH being reprocessed at lower energies by intervening matter (Pacucci et al 2016). Inayoshi et al (2022a) have recently found that Balmer lines for black holes accreting at super-Eddington rates are ∼ 2 − 7 times stronger than in low-𝑧 quasars. This is because the gas is denser and has a larger column density around these DCBHs than in a usual thin disk, and so excitation from 𝑛=2 (populated by trapped Ly𝛼) to 𝑛 ≥ 3 states (via collisions) is more common.…”