Direct Collapse pre-SMBH Objects as Ly$α$ Emitters (2506.18993v1)

Abstract: 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 Ly$\alpha$ photons escape from the central regions of the collapse and serve as a diagnostic for the detection of these pre-SMBH objects? Models assuming spherical collapse have found these photons to be trapped and destroyed. We use Ly$\alpha$ 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 disky and spherical accretion, and formation of bi-conical outflow funnel, we obtain formation of a dense radiatively-driven expanding shell. The Ly$\alpha$ transfer is performed through a Monte Carlo algorithm, accounting for destruction of Ly$\alpha$ photons and emergence of two-photon emission. We find that substantial fraction of Ly$\alpha$ photons can escape through the funnel, and calculate the line profiles, the line peak velocity shift, asymmetry and cuspiness, by varying basic model parameters. The escaping Ly$\alpha$ emission is anisotropic, and sensitive to overall inflow-outflow geometry. The escaping fraction of Ly$\alpha$ radiation exceeds 95% from a $z=10$ pre-SMBH object -- in principle detectable by the JWST NIRSpec in the MOS mode, during $\sim 10^4$seconds for a $10\sigma$ signal-to-noise ratio. Moreover, comparisons with line shapes from high-$z$ galaxies and quasars allow to separate them from pre-SMBH objects based on the line asymmetry -- the pre-SMBH line show a profound asymmetry and extended red tail.