TY - JOUR
T1 - Radiative Transfer in Lyα Nebulae. I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source
AU - Chang, Seok Jun
AU - Yang, Yujin
AU - Seon, Kwang Il
AU - Zabludoff, Ann
AU - Lee, Hee Won
N1 - Funding Information: Y.Y. and S.C. were supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2019R1A2C4069803). K.S. and H.L. were supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (No. 2020R1A2C1005788 and No. 2018R1D1A1B07043944), respectively. A.I.Z. acknowledges support from NSF AST-1715609. She also thanks the hospitality of the Columbia Astrophysics Laboratory at Columbia University, where some of this work was completed. Publisher Copyright: © 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/3/1
Y1 - 2023/3/1
N2 - To understand the mechanism behind high-z Lyα nebulae, we simulate the scattering of Lyα in a H i halo about a central Lyα source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total H i column densities, H i spatial concentrations, and central source galaxies (e.g., with Lyα line widths corresponding to those typical of active galactic nucleus or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Lyα photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Lyα nebulae (∼100 kpc) at total column densities N H I ≥ 1020 cm−2 and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Lyα nebula morphologies: with and without bright cores. Cores are seen when N H I is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. Of all the parameters tested in our smooth or clumpy medium model, N H I dominates the trends. The radial behaviors of the Lyα surface brightness, spectral line shape, and polarization in the clumpy model with covering factor f c ≳ 5 approach those of the smooth model at the same N H I. A clumpy medium with high N H I and low f c ≲ 2 generates Lyα features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump.
AB - To understand the mechanism behind high-z Lyα nebulae, we simulate the scattering of Lyα in a H i halo about a central Lyα source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total H i column densities, H i spatial concentrations, and central source galaxies (e.g., with Lyα line widths corresponding to those typical of active galactic nucleus or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Lyα photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Lyα nebulae (∼100 kpc) at total column densities N H I ≥ 1020 cm−2 and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Lyα nebula morphologies: with and without bright cores. Cores are seen when N H I is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. Of all the parameters tested in our smooth or clumpy medium model, N H I dominates the trends. The radial behaviors of the Lyα surface brightness, spectral line shape, and polarization in the clumpy model with covering factor f c ≳ 5 approach those of the smooth model at the same N H I. A clumpy medium with high N H I and low f c ≲ 2 generates Lyα features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump.
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U2 - 10.3847/1538-4357/acac98
DO - 10.3847/1538-4357/acac98
M3 - Article
SN - 0004-637X
VL - 945
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 100
ER -