标题： 辐射转移在Lyα星云中：I. 用中心源建模连续或团块状球形晕 显示英文标题

标题： Radiative Transfer in Lyα Nebulae: I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source

摘要： 为了理解高-$z$ Ly${\alpha}$ 星云背后的机制，我们模拟了Ly${\alpha}$ 在中心Ly${\alpha}$ 源周围的$\rm H\,I$ 暗物质晕中的散射。 我们首次同时考虑了晕气的平滑和不规则分布，以及一系列外流速度、总 $\rm H\,I$ 柱密度、 $\rm H\,I$ 空间浓度和中心源星系（例如，具有对应于活动星系核或恒星形成星系典型值的 Ly ${\alpha}$ 线宽）。 我们计算了由原子氢散射的 Ly ${\alpha}$ 光子的空间频率扩散和偏振。 我们的仅散射模型在总柱密度 $N_{\rm HI} \geq 10^{20} \rm cm^{-2}$ 下再现了 Ly ${\alpha}$ 星云的典型大小（ $\sim 100\,$kpc），并预测了正、平和负的偏振径向梯度范围。 我们还发现Ly${\alpha}$星云形态的两个一般类别：有明亮核心和没有明亮核心。 当$N_{\rm HI}$较低时可以看到核心，即当中心源直接可见时，且与偏振跳跃有关，在晕核中心之外的偏振径向分布急剧增加。 在我们平滑或致密介质模型中测试的所有参数中，$N_{\rm HI}$主导了趋势。 在覆盖因子为$f_c \gtrsim 5$的致密模型中，Ly${\alpha}$表面亮度、光谱线形状和偏振的径向行为在相同$N_{\rm HI}$下接近平滑模型的行为。 一个具有高$N_{\rm HI}$和低$f_c \lesssim 2$的不均匀介质通过散射产生平滑模型无法产生的 Ly${\alpha}$特征：明亮的核心、对称的谱线轮廓和偏振跃变。 显示英文摘要

摘要： To understand the mechanism behind high-$z$ Ly${\alpha}$ nebulae, we simulate the scattering of Ly${\alpha}$ in a $\rm H\,I$ halo about a central Ly${\alpha}$ source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total $\rm H\,I$ column densities, $\rm H\,I$ spatial concentrations, and central source galaxies (e.g., with Ly${\alpha}$ line widths corresponding to those typical of AGN or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Ly${\alpha}$ photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Ly${\alpha}$ nebulae ($\sim 100\,$kpc) at total column densities $N_{\rm HI} \geq 10^{20} \rm cm^{-2}$ and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Ly${\alpha}$ nebula morphologies: with and without bright cores. Cores are seen when $N_{\rm HI}$ 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, $N_{\rm HI}$ dominates the trends. The radial behaviors of the Ly${\alpha}$ surface brightness, spectral line shape, and polarization in the clumpy model with covering factor $f_c \gtrsim 5$ approach those of the smooth model at the same $N_{\rm HI}$. A clumpy medium with high $N_{\rm HI}$ and low $f_c \lesssim 2$ generates Ly${\alpha}$ features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump.