EFFECT OF DUST ON Ly{alpha} PHOTON TRANSFER IN AN OPTICALLY THICK HALO

Journal Article · Sat Oct 01 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/739/2/91; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21587462

Yang, Yang; Chiwang, Shu ^[1]; Roy, Ishani ^[2]; Lizhi, Fang ^[3]

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1. Division of Applied Mathematics, Brown University, Providence, RI 02912 (United States)
2. Computing Laboratory, University of Oxford, Oxford, OX1 3QD (United Kingdom)
3. Department of Physics, University of Arizona, Tucson, AZ 85721 (United States)

We investigate the effects of dust on Ly{alpha} photons emergent from an optically thick medium by solving the integro-differential equation of radiative transfer of resonant photons. To solve the differential equations numerically, we use the weighted essentially non-oscillatory method. Although the effects of dust on radiative transfer are well known, the resonant scattering of Ly{alpha} photons makes the problem non-trivial. For instance, if the medium has an optical depth of dust absorption and scattering of {tau}{sub a} >> 1, {tau} >> 1, and {tau} >> {tau}{sub a}, the effective absorption optical depth in a random walk scenario would be equal to {radical}({tau}{sub a}({tau}{sub a}+{tau})). We show, however, that for a resonant scattering at frequency {nu}{sub 0}, the effective absorption optical depth would be even larger than {tau}({nu}{sub 0}). If the cross section of dust scattering and absorption is frequency-independent, the double-peaked structure of the frequency profile given by the resonant scattering is basically dust-independent. That is, dust causes neither narrowing nor widening of the width of the double-peaked profile. One more result is that the timescales of the Ly{alpha} photon transfer in an optically thick halo are also basically independent of the dust scattering, even when the scattering is anisotropic. This is because those timescales are mainly determined by the transfer in the frequency space, while dust scattering, either isotropic or anisotropic, does not affect the behavior of the transfer in the frequency space when the cross section of scattering is wavelength-independent. This result does not support the speculation that dust will lead to the smoothing of the brightness distribution of a Ly{alpha} photon source with an optically thick halo.

• OSTI ID: 21587462
• Journal Information: Astrophysical Journal, Vol. 739, Issue 2; Other Information: DOI: 10.1088/0004-637X/739/2/91; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
DIFFERENTIAL EQUATIONS
DUSTS
GRAPH THEORY
INTEGRO-DIFFERENTIAL EQUATIONS
LYMAN LINES
PHOTONS
RADIANT HEAT TRANSFER
RESONANCE SCATTERING
BOSONS
ELEMENTARY PARTICLES
ENERGY TRANSFER
EQUATIONS
HEAT TRANSFER
INELASTIC SCATTERING
MASSLESS PARTICLES
MATHEMATICS
SCATTERING
SORPTION