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arXiv 2009.09882astro-ph.GA
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莱曼连续体泄漏星系的逃逸分数和观测到的线发射

Reconciling escape fractions and observed line emission in Lyman-continuum-leaking galaxies

L. Ramambason, D. Schaerer, G. Stasińska, Y. I. Izotov, N. G. Guseva, J. M Vílchez, R. Amorín, C. Morisset

摘要:

发现和阐明Lyman连续谱(LyC)发射星系的性质是理解宇宙再电离的重要一步。虽然最近发现的z - 0.3-0.4 LyC发射体显示出强的光学发射线,但尚未建立考虑电离光子逃逸和这些星系的非均匀星际介质(ISM)几何形状的一致定量光电离模型。因此,我们构建一个和两个区域的光电离模型占所观察到的LyC逃逸,我们比较所观察到的发射线测量。我们发现,单区密度约束的光电离模型不能再现的LyC泄漏的发射线,因为它们系统地低估了低电离势的物种的线,如[OI]和[SII]。引入一个两区模型,不同的电离参数和一个可变的覆盖分数,其中一个区域是密度有界的,我们表明,所观察到的发射线比和逃逸分数的LyC发射器很好地再现。在一些LyC泄漏中观察到的[OI]过量可以在该模型中自然地解释,例如,通过从低电离和低填充因子气体发射。具有高逃逸分数(fesc > 38%)的LyC发射体在[OI] 6300 A和[SII] 6716,6731 A中都是不足的。我们还证实,[SII]缺陷可用于选择LyC发射体候选者。最后,我们发现了一个可能的二分法的迹象,在逃逸机制的LyC光子之间的星系相对较低(fesc < 10%)和较高的逃逸分数。我们的结论是,两区光电离模型是足够的,需要解释所观察到的发射线特性的z - 0.3-0.4 LyC发射器。这些模型提供了第一步使用的光学发射线和它们的比率作为定量诊断的LyC逃离星系。

英文摘要:

Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step for our understanding of cosmic reionization. Although the z - 0.3-0.4 LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. We hence construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. We find that one-zone density-bounded photoionization models cannot reproduce the emission lines of the LyC leakers because they systematically underpredict the lines of species of low ionization potential, as [OI] and [SII]. Introducing a two-zone model, with differing ionization parameter and a variable covering fraction and where one of the zones is density-bounded, we show that the observed emission line ratios and escape fractions of the LyC emitters are well reproduced. The [OI] excess, which is observed in some LyC leakers, can be naturally explained in this model, e.g., by emission from low-ionization and low-filling-factor gas. LyC emitters with a high escape fraction (fesc > 38%) are deficient both in [OI]6300A and in [SII]6716,6731A. We also confirm that a [SII] deficiency can be used to select LyC emitter candidates. Finally, we find indications for a possible dichotomy in terms of escape mechanisms for LyC photons between galaxies with relatively low (fesc < 10%) and higher escape fractions. We conclude that two-zone photoionization models are sufficient and required to explain the observed emission line properties of z - 0.3-0.4 LyC emitters. These models provide a first step towards the use of optical emission lines and their ratios as quantitative diagnostics of LyC escape from galaxies.

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