ART2: coupling Lyα line and multi-wavelength continuum radiative transfer

Abstract

Narrow‐band Lyα line and broad‐band continuum have played important roles in the discovery of high‐redshift galaxies in recent years. Hence, it is crucial to study the radiative transfer of both Lyα and continuum photons in the context of galaxy formation and evolution in order to understand the nature of distant galaxies. Here, we present a three‐dimensional Monte Carlo radiative transfer code, All‐wavelength Radiative Transfer with Adaptive Refinement Tree (), which couples Lyα line and multi‐wavelength continuum, for the study of panchromatic properties of galaxies and interstellar medium. This code is based on the original version of Li et al., and features three essential modules: continuum emission from X‐ray to radio, Lyα emission from both recombination and collisional excitation, and ionization of neutral hydrogen. The coupling of these three modules, together with an adaptive refinement grid, enables a self‐consistent and accurate calculation of the Lyα properties, which depend strongly on the UV continuum, ionization structure and dust content of the object. Moreover, it efficiently produces multi‐wavelength properties, such as the spectral energy distribution and images, for direct comparison with multi‐band observations. As an example, we apply to a cosmological simulation that includes both star formation and black hole growth, and study in detail a sample of massive galaxies at redshifts z= 3.1–10.2. We find that these galaxies are Lyα emitters (LAEs), whose Lyα emission traces the dense gas region, and that their Lyα lines show a shape characteristic of gas inflow. Furthermore, the Lyα properties, including photon escape fraction, emergent luminosity and equivalent width, change with time and environment. Our results suggest that LAEs evolve with redshift, and that early LAEs such as the most distant one detected at z∼ 8.6 may be dwarf galaxies with a high star formation rate fuelled by infall of cold gas, and a low Lyα escape fraction.

COLD ACCRETION IN EARLY GALAXY FORMATION AND ITS ${\rm Ly}\alpha $ SIGNATURES

“…We first calculate the ionization structure due to internal stellar sources and then simulate the Lyα RT. We cast N ph = 10 5 photon packets for each ionizing, Lyα, and non-ionizing component, which showed good convergence (Yajima et al 2012a(Yajima et al , 2012b. In addition, interstellar dust is included to consider the dust extinction of Lyα and continuum photons, and to simulate the dust thermal emission (see also Yajima et al 2012a).…”

“…The ART 2 code includes continuum photons from X-ray to radio, the Lyα line, and the ionization structure in the adaptive refinement grids. The detailed prescriptions of the code were presented in Li et al (2008) and Yajima et al (2012a). The Lyα emission comes from the recombination and de-excitation process, (Osterbrock & Ferland 2006).…”

“…More recently, Di Matteo et al (2012) suggested that massive galaxies at z  6 can grow by cold accretion and evolve with black holes. Such streams of cold gas may produce a large number of Lyα photons via the excitation cooling process and give rise to the Lyα emission detected in the early galaxies (Dijkstra & Loeb 2009;Faucher-Giguère et al 2010;Latif et al 2011;Yajima et al 2012aYajima et al , 2012b.…”

“…The simulation uses the Aquila initial condition and follows the formation and evolution of a Milky-Way-size galaxy (Wadepuhl & Springel 2011;Scannapieco et al 2012 zoom-in region, which is ideal for studying the gas inflow on a large scale. The RT calculations use the three-dimensional Monte Carlo RT code ART 2 by Li et al (2008) and Yajima et al (2012a). The ART 2 code couples the multi-wavelength continuum, the Lyα line, and the ionization of hydrogen, which is critical for studying the Lyα and multi-band properties of early galaxies.…”

Inclination dependence of Lyman-αproperties in a turbulent disk galaxy

“…For quantifying the inclination dependence of Lyα transmission, more realistic models of LAEs are needed, for example, for estimating how large-scale surveys are affected by a possible alignment of galaxies with the large-scale structure in combination with inclination effects (Hirata 2009) or other correlations with the large-scale structure (Zheng et al 2010(Zheng et al , 2011Behrens & Niemeyer 2013). While a number of studies of the Lyα transport with more realistic LAEs in cosmological contexts exist (e.g., Tasitsiomi 2006; Laursen et al 2009;Yajima et al 2012;Barnes et al 2011;Faucher-Giguere et al 2010) only the work by Verhamme et al (2012, hereafter VDB12) investigates the effects of directional dependence on the basis of high-resolution, dusty, isolated disk simulations in detail. Their work includes radiative transfer calculations in the resolved interstellar medium (ISM) as well as in the transfer of continuum photons for estimating the Lyα equivalent width (EW).…”