The Lyman-alpha signature of the first galaxies

Abstract

We present the Cosmic Lyman-$\alpha$ Transfer code (COLT), a massively parallel Monte-Carlo radiative transfer code, to simulate Lyman-$\alpha$ (Ly$\alpha$) resonant scattering through neutral hydrogen as a probe of the first galaxies. We explore the interaction of centrally produced Ly$\alpha$ radiation with the host galactic environment. Ly$\alpha$ photons emitted from the luminous starburst region escape with characteristic features in the line profile depending on the density distribution, ionization structure, and bulk velocity fields. For example, anisotropic ionization exhibits a tall peak close to line centre with a skewed tail that drops off gradually. Idealized models of first galaxies explore the effect of mass, anisotropic H II regions, and radiation pressure driven winds on Ly$\alpha$ observables. We employ mesh refinement to resolve critical structures. We also post-process an ab initio cosmological simulation and examine images captured at various escape distances within the 1 Mpc${}^3$ comoving volume. Finally, we discuss the emergent spectra and surface brightness profiles of these objects in the context of high-$z$ observations. The first galaxies will likely be observed through the red damping wing of the Ly$\alpha$ line. Observations will be biased toward galaxies with an intrinsic red peak located far from line centre that reside in extensive H II super bubbles, which allows Hubble flow to sufficiently redshift photons away from line centre and facilitate transmission through the intergalactic medium (IGM). Even with gravitational lensing to boost the luminosity this preliminary work indicates that Ly$\alpha$ emission from stellar clusters within haloes of $M_{\mathrm{vir}}<10^9{\mathrm{M}}_{\odot }$ is generally too faint to be detected by the James Webb Space Telescope (JWST).

28 pages, 22 figures, MNRAS, in press

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Cited by in corpus (6)

• Lyman-alpha radiation hydrodynamics of galactic winds before cosmic reionization
• Radiative effects during the assembly of direct collapse black holes
• Boosting Lya and HeII 1640A Line Fluxes from Pop III Galaxies: Stochastic IMF Sampling and Departures from Case-B
• On the effect of Lyman alpha trapping during the initial collapse of massive black hole seeds
• Contribution of the first galaxies to the cosmic far-infrared/sub-millimeter background - I. Mean background level
• SEURAT: SPH scheme extended with ultraviolet line radiative transfer