Angular Distribution of Ly(alpha) Resonant Photons Emergent from Optically Thick Medium
Abstract
We investigate the angular distribution of Ly(alpha) photons transferring in or emergent from an optically thick medium. Since the evolutions of specific intensity I in the frequency space and the angular space are coupled from each other, we first develop the WENO numerical solver in order to find the time-dependent solutions of the integro-differential equation of I in the space of frequency and angular simultaneously. We show first that the solutions with the Eddington approximation, which assume I to be linearly dependent on the angular variable mu, yield similar frequency profiles of the photon flux as that without the Eddington approximation. However, the solutions of the mu distribution evolution are significantly different from that given by Eddington approximation. First, the angular distribution of I are found to be substantially dependent on the frequency of photons. For photons with the resonant frequency nu0, I contains only a linear term of mu;. For photons with frequency at the double peaks of the flux, the mu-distribution is highly anisotropic, in which most photons are in the direction of radial forward. Moreover, either at nu0 or at the double peaks, the mu distributions actually are independent of the initial mu distribution of photons of the source. This is because the photons with frequency either of nu0 or of the double peaks have undergone the process of forgetting their initial conditions due to the resonant scattering. We also show that the optically thick medium is a collimator of photons at the double peaks. Photons from the double peaks form a forward beam with very small spread angle.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 26, 2012
- Accession Number
- ADA557714
Entities
People
- Chi-Wang Shu
- Ishani Roy
- Li-zhi Fang
- Yang Yang
Organizations
- Brown University