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arXiv · 1602.07639

Evidence for a direct collapse black hole in the Lyman-alpha source CR7

Aaron Smith·Volker Bromm·Abraham Loeb
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Abstract

Throughout the epoch of reionization the most luminous Lyα emitters are capable of ionizing their own local bubbles. The CR7 galaxy at $z \approx 6.6$ stands out for its combination of exceptionally bright Lyα and HeII 1640 Angstrom line emission but absence of metal lines. As a result CR7 may be the first viable candidate host of a young primordial starburst or direct collapse black hole. High-resolution spectroscopy reveals a +160 km s$^{-1}$ velocity offset between the Lyα and HeII line peaks while the spatial extent of the Lyα emitting region is $\sim 16$ kpc. The observables are indicative of an outflow signature produced by a strong central source. We present one-dimensional radiation-hydrodynamics simulations incorporating accurate Lyα feedback and ionizing radiation to investigate the nature of the CR7 source. We find that a Population III star cluster with $10^5$ K blackbody emission ionizes its environment too efficiently to generate a significant velocity offset. However, a massive black hole with a nonthermal Compton-thick spectrum is able to reproduce the Lyα signatures as a result of higher photon trapping and longer potential lifetime. For both sources, Lyα radiation pressure turns out to be dynamically important.

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Aaron Smith, Volker Bromm, Abraham Loeb. 2016-05-10. Evidence for a direct collapse black hole in the Lyman-alpha source CR7. https://doi.org/10.1093/mnras%2Fstw1129

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