3-cm Fine Structure Masers: A Unique Signature of Supermassive Black Hole Formation via Direct Collapse in the Early Universe

Understand

The direct collapse black hole (DCBH) scenario describes the isothermal collapse of a pristine gas cloud directly into a massive, M_BH=10^4-10^6 M_sun black hole.

• In this paper we show that large HI column densities of primordial gas at T~10^4 K with low molecular abundance - which represent key aspects of the DCBH scenario - provide optimal conditions for pumping of the 2p-level of atomic hydrogen by trapped Lyman alpha (Lya) photons.
• This Lya pumping mechanism gives rise to inverted level population of the 2s_1/2-2p_3/2 transition, and therefore to stimulated fine structure emission at 3.04 cm (rest-frame).
• We show that simplified models of the DCBH scenario amplify the CMB by up to a factor of 10^5, above which the maser saturates.