Direct Collapse Pre-supermassive Black Hole Objects as Ly$\alpha$ Emitters

TL;DR

This study models Ly$ ext{\alpha}$ photon escape from direct collapse pre-supermassive black hole objects, revealing they can produce detectable, anisotropic Ly$ ext{\alpha}$ emission with distinctive line profiles, aiding early universe SMBH detection.

Contribution

It introduces a detailed radiation transfer model for Ly$ ext{\alpha}$ emission in pre-SMBH objects with complex inflow-outflow geometries, predicting observable signatures for JWST.

Findings

Ly$ ext{\alpha}$ photons can escape through funnel structures with over 95% efficiency.

Escaping Ly$ ext{\alpha}$ emission is anisotropic and sensitive to geometry.

Pre-SMBH Ly$ ext{\alpha}$ lines show distinctive asymmetry and red tails.

Abstract

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 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 of 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 disk and spherical accretion, and formation of a biconical outflow funnel, we obtain the formation of a dense radiatively driven expanding shell. The Ly$\alpha$ transfer is performed using a Monte Carlo algorithm, accounting for the destruction of Ly$\alpha$ photons and the emergence of two-photon emission. We find that a 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 the 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 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.