Lyman-alpha radiation hydrodynamics of galactic winds before cosmic reionization

TL;DR

This study uses advanced radiation-hydrodynamics simulations to explore how Lyman-alpha radiation pressure influences early galaxy formation and outflows before cosmic reionization, highlighting the role of Ly{eta} feedback and its observational signatures.

Contribution

It presents the first self-consistent Ly{eta} radiation-hydrodynamics simulations coupling COLT with hydrodynamics, revealing Ly{eta} feedback effects on protogalactic outflows and Ly{eta} signatures for different ionizing sources.

Findings

Ly{eta} feedback can significantly enhance shell velocities in early galaxies.

Radiative feedback alone can eject baryons from low-mass protogalaxies into the IGM.

Ly{eta} spectra are shaped by gas dynamics, showing differences between stellar and black hole sources.

Abstract

The dynamical impact of Lyman-alpha (Ly{\alpha}) radiation pressure on galaxy formation depends on the rate and duration of momentum transfer between Ly{\alpha} photons and neutral hydrogen gas. Although photon trapping has the potential to multiply the effective force, ionizing radiation from stellar sources may relieve the Ly{\alpha} pressure before appreciably affecting the kinematics of the host galaxy or efficiently coupling Ly{\alpha} photons to the outflow. We present self-consistent Ly{\alpha} radiation-hydrodynamics simulations of high-$z$ galaxy environments by coupling the Cosmic Ly{\alpha} Transfer code (COLT) with spherically symmetric Lagrangian frame hydrodynamics. The accurate but computationally expensive Monte-Carlo radiative transfer calculations are feasible under the one-dimensional approximation. The initial starburst drives an expanding shell of gas from the centre and in certain cases Ly{\alpha} feedback significantly enhances the shell velocity. Radiative feedback alone is capable of ejecting baryons into the intergalactic medium (IGM) for protogalaxies with a virial mass of $M_{\rm vir} \lesssim 10^8~{\rm M}_\odot$. We compare the Ly{\alpha} signatures of Population III stars with $10^5$ K blackbody emission to that of direct collapse black holes with a nonthermal Compton-thick spectrum and find substantial differences if the Ly{\alpha} spectra are shaped by gas pushed by Ly{\alpha} radiation-driven winds. For both sources, the flux emerging from the galaxy is reprocessed by the IGM such that the observed Ly{\alpha} luminosity is reduced significantly and the time-averaged velocity offset of the Ly{\alpha} peak is shifted redward.