标题： 中性气体特性及极端绿色豌豆星系中Ly$α$逃逸 显示英文标题

标题： Neutral Gas Properties and Ly$α$ Escape in Extreme Green Pea Galaxies

摘要： 调控Ly$\alpha$光子和电离辐射逃逸的机制仍不明确。 为了研究这些过程，我们分析了一个绿豌豆（GP）天体J160810+352809（以下简称J1608）的VLA 21厘米观测数据，以及17个GP星系在$z<0.2$的HST COS光谱。 所有天体都高度电离：J1608的[O III] $\lambda5007$/[O II] $\lambda3727$是SDSS中形成恒星的星系中最高的，而17个GP的[O III]/[O II] $\geq6.6$。 我们设定了J1608的HI质量上限为$\log M_{HI}/M_\odot=8.4$，与类似质量的矮星系相比处于或低于平均水平。 在COS样本中，八个GPs显示Ly$\alpha$吸收成分，其中六个同时具有Ly$\alpha$发射。 从Ly$\alpha$吸收得出的HI柱密度很高，$\log N_{HI}/$cm$^{-2}=19-21$，远高于LyC光学厚极限。 使用低电离吸收线，我们测量了覆盖分数($f_{\mbox{cov}}$)为$0.1-1$，并发现$f_{\mbox{cov}}$与Ly$\alpha$逃逸分数强烈负相关。 低覆盖分数可能促进Ly$\alpha$和LyC通过致密中性区域逃逸。 具有$f_{\mbox{cov}}\sim1$的GPs都有低中性气体速度，而具有较低$f_{\mbox{cov}}=0.2-0.6$的GPs有更大的速度范围。 传统机械反馈在某些情况下可能有助于建立低$f_{\mbox{cov}}$，而其他过程可能对低速度的GPs很重要。 最后，我们将$f_{\mbox{cov}}$与提出的LyC逃逸指标进行比较。 电离光子逃逸可能取决于中性气体几何结构和动力学的组合，这使得使用发射线诊断来识别LyC发射体变得复杂。 显示英文摘要

摘要： Mechanisms regulating the escape of Ly$\alpha$ photons and ionizing radiation remain poorly understood. To study these processes we analyze VLA 21cm observations of one Green Pea (GP), J160810+352809 (hereafter J1608), and HST COS spectra of 17 GP galaxies at $z<0.2$. All are highly ionized: J1608 has the highest [O III] $\lambda5007$/[O II] $\lambda3727$ for star-forming galaxies in SDSS, and the 17 GPs have [O III]/[O II] $\geq6.6$. We set an upper limit on J1608's HI mass of $\log M_{HI}/M_\odot=8.4$, near or below average compared to similar mass dwarf galaxies. In the COS sample, eight GPs show Ly$\alpha$ absorption components, six of which also have Ly$\alpha$ emission. The HI column densities derived from Ly$\alpha$ absorption are high, $\log N_{HI}/$cm$^{-2}=19-21$, well above the LyC optically thick limit. Using low-ionization absorption lines, we measure covering fractions ($f_{\mbox{cov}}$) of $0.1-1$, and find that $f_{\mbox{cov}}$ strongly anti-correlates with Ly$\alpha$ escape fraction. Low covering fractions may facilitate Ly$\alpha$ and LyC escape through dense neutral regions. GPs with $f_{\mbox{cov}}\sim1$ all have low neutral gas velocities, while GPs with lower $f_{\mbox{cov}}=0.2-0.6$ have a larger range of velocities. Conventional mechanical feedback may help establish low $f_{\mbox{cov}}$ in some cases, whereas other processes may be important for GPs with low velocities. Finally, we compare $f_{\mbox{cov}}$ with proposed indicators of LyC escape. Ionizing photon escape likely depends on a combination of neutral gas geometry and kinematics, complicating the use of emission-line diagnostics for identifying LyC emitters.