Radiative transfer

About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.

Massive Star Formation in Galaxies: Radiative transfer models of the UV to mm emission of starburst galaxies

Abstract: We present illustrative models for the UV to millimeter emission of starburst galaxies which are treated as an ensemble of optically thick giant molecular clouds (GMCs) centrally illuminated by recently formed stars. The models follow the evolution of the GMCs due to the ionization-induced expansion of the HII regions and the evolution of the stellar population within the GMC according to the Bruzual & Charlot stellar population synthesis models. The effect of transiently heated dust grains/PAHs to the radiative transfer, as well as multiple scattering, is taken into account. The expansion of the HII regions and the formation of a narrow neutral shell naturally explains why the emission from PAHs dominates over that from hot dust in the near to mid-IR, an emerging characteristic of the infrared spectra of starburst galaxies. The models allow us to relate the observed properties of a galaxy to its age and star formation history. We find that exponentially decaying 10^7-10^8 yrs old bursts can explain the IRAS colours of starburst galaxies. The models are also shown to account satisfactorily for the multiwavelength data on the prototypical starburst galaxy M82 and NGC6090, a starburst galaxy recently observed by ISO. In M82 we find evidence for two bursts separated by 10^7yrs. In NGC6090 we find that at least part of the far-IR excess may be due to the age of the burst (6.4 x 10^7yrs). We also make predictions about the evolution of the luminosity of starbursts at different wavelengths which indicate that far-IR surveys may preferentially detect older starbursts than mid-IR surveys.

A study of radiative properties of fractal soot aggregates using the superposition T-matrix method

Abstract: We employ the numerically exact superposition T-matrix method to perform extensive computations of scattering and absorption properties of soot aggregates with varying state of compactness and size. The fractal dimension, Df, is used to quantify the geometrical mass dispersion of the clusters. The optical properties of soot aggregates for a given fractal dimension are complex functions of the refractive index of the material m, the number of monomers NS, and the monomer radius a. It is shown that for smaller values of a, the absorption cross section tends to be relatively constant when Dfo2 but increases rapidly when Df42. However, a systematic reduction in light absorption with Df is observed for clusters with sufficiently large NS, m, and a. The scattering cross section and single-scattering albedo increase monotonically as fractals evolve from chain-like to more densely packed morphologies, which is a strong manifestation of the increasing importance of scattering interaction among spherules. Overall, the results for soot fractals differ profoundly from those calculated for the respective volume-equivalent soot spheres as well as for the respective external mixtures of soot monomers under the assumption that there are no electromagnetic interactions between the monomers. The climate-research implications of our results are discussed.

Linear analysis of an oscillatory instability of radiative shock waves

Abstract: We present a linear stability analysis of a planar radiative shock with cooling function ..lambda..proportionalT/sup ..cap alpha../. We investigate an oscillatory instability similar to that found in numerical calculations of accretion onto degenerate dwarfs by Langer, Chanmugam, and Shaviv. Our analysis shows that multiple modes of oscillations are unstable for ..cap alpha..< or approx. =0.4 for the fundamental mode and ..cap alpha..< or approx. =0.8 for the first and second overtone modes. The oscillation frequency is 0.3 x/sub s/0/u/sub in/ for the fundamental mode and ranges from 0.6 x/sub s/0/u/sub in/ to 1.0 x/sub s/0/u/sub in/ for the first overtone mode for ..cap alpha.. between -1 and 2, where x/sub s/0 is the results should be applicable both to accretion onto compact objects and to radiative shock waves in the interstellar medium. The instability may explain the inability of the steady state shock wave emission models to reproduce certain observations of old supernova remnants and Herbig-Haro objects.

A generic dynamical model of gamma-ray burst remnants

Abstract: The conventional generic model is deemed to explain the dynamics of $\gamma$-ray burst remnants very well, no matter whether they are adiabatic or highly radiative. However, we find that for adiabatic expansion, the model could not reproduce the Sedov solution in the non-relativistic phase, thus the model needs to be revised. In the present paper, a new differential equation is derived. The generic model based on this equation has been shown to be correct for both radiative and adiabatic fireballs, and in both ultra-relativistic and non-relativistic phase.

Comments on the classical theory of energy transfer

Abstract: Energy transfer from an emitting molecule to an absorbing half−space is considered from the viewpoint of electromagnetic theory. The lifetime of a dipole emitter in the presence of a mirror is determined through a calculation of the complex Poynting vector in the dielectric surrounding the dipole. This method has the advantage over previous approaches to this problem in that the radiative and nonradiative components of the lifetime expression may be rigorously separated. The influence on emitter lifetime of a mirror of finite thickness is also described. A simple expression is derived describing the energy transfer rate in these layered systems. It is shown that nonradiative energy transfer results from coupling of the near field of the dipole to the surface plasmon modes in the metallic absorber. The Forster energy transfer rate law is discussed in the context of the present theory.