Title:	3-cm Fine structure masers: a unique signature of supermassive black hole formation via direct collapse in the early universe
Authors:	Dukstra, Mark Sethi, S.K. Loeb, Abraham
Issue Date:	20-Mar-2016
Publisher:	IOP Sciences for The American Astronomical Society
Citation:	Astrophysical Journal, 2016, Vol. 820, p10
Abstract:	The direct collapse black hole (DCBH) scenario describes the isothermal collapse of a pristine gas cloud directly into a massive, ${M}_{\mathrm{BH}}\;=$ 104–106${M}_{\odot }$ black hole. In this paper we show that large H i column densities of primordial gas at $T\sim {10}^{4}$ K with low molecular abundance—which represent key aspects of the DCBH scenario—provide optimal conditions for the pumping of the 2p-level of atomic hydrogen by trapped Lyα photons. This Lyα pumping mechanism gives rise to an inverted level population of the $2{s}_{1/2}-2{p}_{3/2}$ transition, and therefore also gives rise to stimulated fine structure emission at $\lambda =3.04\;\mathrm{cm}$ (rest-frame). We show that simplified models of the DCBH scenario amplify the CMB by up to a factor of $\sim {10}^{5}$, above which the maser saturates. Hyperfine splitting of the 3 cm transition gives rise to a characteristic broad (FWHM ~ tens of MHz in the observers frame) asymmetric line profile. This signal subtends an angular scale of ~1–10 mas, which translates to a flux of ~0.3–3 μJy, which is detectable with ultra-deep surveys being planned with SKA1-MID. While challenging, as the signal is visible for a fraction of the collapse time of the cloud, the matching required physical conditions imply that a detection of the redshifted 3-cm emission line could provide direct evidence for the DCBH scenario.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/6445
ISSN:	0004-637X 1538-4357-(Online)
Alternative Location:	http://adsabs.harvard.edu/abs/2016ApJ...820...10D http://arxiv.org/abs/1601.04712 http://dx.doi.org/10.3847/0004-637X/820/1/10
Copyright:	2016, The American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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