Direct Collapse Pre-supermassive Black Hole Objects as Lyα Emitters

The Direct Collapse scenario to form the supermassive black hole (SMBH) seeds offers the most promising way to explain the origin of quasars at z > 7. Assuming atomic primordial gas, can Lyα photons escape from the central regions of the collapse and serve as a diagnostic for the detection of these pre-SMBH objects? Models of spherical collapse have found these photons to be trapped and destroyed. We use Lyα radiation transfer within the inflow-outflow geometry, based on earlier zoom-in cosmological modeling involving radiation transfer and magnetic forces. Adopting geometry that includes ongoing disk and spherical accretion, and formation of a biconical outflow funnel, we obtain the formation of a dense radiatively driven expanding shell. The Lyα transfer is performed using a Monte Carlo algorithm, accounting for the destruction of Lyα photons and the emergence of two-photon emission. We find that a substantial fraction of Lyα photons can escape through the funnel and calculate the line profiles, their line peak velocity shift, asymmetry, and cuspiness, by varying basic model parameters. The escaping Lyα emission is anisotropic and sensitive to the overall inflow-outflow geometry. The escaping fraction of Lyα radiation exceeds 95% from a z = 10 pre-SMBH object in principle detectable by the JWST NIRSpec in the multiobject spectroscopy mode, during ∼10⁴ s for a 10σ signal-to-noise ratio. Moreover, comparisons with line shapes from high-z galaxies and quasars allow us to separate them from pre-SMBH objects based on the line shape: the pre-SMBH lines show a profound asymmetry and extended red tail.