Radiative Transfer in Lyα Nebulae. I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2023
- DOI:
- 10.3847/1538-4357/acac98
- arXiv:
- arXiv:2212.09630
- Bibcode:
- 2023ApJ...945..100C
- Keywords:
-
- Radiative transfer;
- Radiative transfer simulations;
- Lyman-alpha galaxies;
- Emission nebulae;
- 1335;
- 1967;
- 978;
- 461;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 42 pages, 27 figures, accepted for publication in ApJ, Comments welcome!