Lyman<i>α</i>radiation hydrodynamics of galactic winds before cosmic reionization

Abstract

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