The Lyman α signature of the first galaxies

Abstract

We present the Cosmic Lyman-α Transfer code (COLT), a massively parallel Monte-Carlo radiative transfer code, to simulate Lyman-α (Lyα) resonant scattering through neutral hydrogen as a probe of the first galaxies. We explore the interaction of centrally produced Lyα radiation with the host galactic environment. Lyα 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 Lyα observables. We employ mesh refinement to resolve critical structures. We also post-process an ab initio cosmological simulation and examine images captured at various 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 Lyα 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. Even with gravitational lensing to boost the luminosity this preliminary work indicates that Lyα emission from stellar clusters within haloes of M vir < 10 9 M is generally too faint to be detected by the James Webb Space Telescope (JWST).

The first galaxies: simulating their feedback-regulated assembly

“…Although the recombination luminosity in Lyα is higher than that in Hα, in reality Lyα photons are more likely to scatter in the neutral IGM (e.g. Dijkstra & Wyithe 2007;Smith et al 2015), and thus the observed flux in Lyα may be substantially lower than implied by the intrinsic luminosity. Because of the hard spectra of massive Pop III stars, strong nebular emission, particularly in the He II λ1640 line, has been suggested as a possible observable signature of metal-free Pop III galaxies (e.g.…”

Evidence for a direct collapse black hole in the Lymanαsource CR7

“…to produce the necessary offset, where we have normalized the gas temperature according to T 4 ≡ T/(10 4 K), see the discussion following equation (34) in Smith et al (2015). Assuming an approximately isothermal density profile, clump A would have τ 0 10 11 if it remained neutral.…”

“…As predicted by Partridge & Peebles (1967), proto-galactic star formation would produce powerful intrinsic Lyα luminosities, although the increasing neutral hydrogen fraction in the diffuse intergalactic medium (IGM) significantly suppresses Lyα transmission for sources at z > 6.5 (Dijkstra 2014; Mesinger et al 2015). Still, galaxies with strong Lyα emission are more likely to be detected with substantial outflows or clustered within locally ionized bubbles and web-like morphologies (Jensen et al 2013;Kakiichi et al 2015;Smith et al 2015). Despite attenuation from the neutral IGM one might hope to infer properties of the emission source, galaxy, and IGM based on the altered Lyα line profile, physical size of the Lyα emitting region, continuum spectral energy distribution (SED), and relative strength of Lyα, Hα, and He ii 1640 Å nebular emission lines (Schaerer 2002;Johnson et al 2009;.…”

Contribution of the first galaxies to the cosmic far-infrared/sub-millimeter background – I. Mean background level

“…To construct the density profile for the gaseous component, we adopt an isothermal power law of the form ∼ r −2 , as it provides a good description of a virialized system (Binney & Tremaine 2008). Following Smith et al (2015), we consider a non-cuspy 'core', consistent with observations of low surface brightness galaxies (e.g. Kormendy et al 2009).…”