Abstract
Abstract
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.
Funder
National Research Foundation of Korea
National Science Foundation
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
6 articles.
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