The Ionization State of Sodium in Galactic Winds

The Ionization State of Sodium in Galactic Winds
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银河风中钠的电离态

DOI：
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发表时间：
2006
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影响因子：
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通讯作者：
T. Thompson
T. Thompson
中科院分区：
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文献类型：
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作者：
N. Murray;C. Martin;E. Quataert;T. Thompson

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大约80%的超发光红外星系(ULIRG)在中性钠的共振线上表现出蓝移吸收，这表明冷风在这类天体中很常见，正如Rupke等人所表明的那样。马丁也是。由这些吸收谱线表示的中性钠(Na)柱为~1013-(3×1014)cm-2，这是一个令人惊讶的结果，因为测得的辐射光度范围只有4倍。我们表明ULIRG流出的气体可能处于光电离平衡。Goldader等人的非常小的ULIRG样本。演示了UV通量与FIR通量的比率在不同对象之间的变化系数约为100。而Goldader等人。样品与Rupke等人的样品不重叠。而Martin，我们证明了在固定的质量通量和密度下，UV通量的如此大的变化将在中性钠柱中产生类似的变化。然而，如果冷气体处于压力平衡状态，而热流出的质量损失率与恒星形成率相似，则电离态的范围要小得多。马丁和鲁普克等人对物体的紫外线通量的测量。星表将最终确定光致电离效应是否是钠柱中出现的巨大差异的原因。如果是这样的话，冷风中气体密度和质量损失率的测定将随之而来，随之而来的是我们对风驱动机制和星系对其周围的反馈效应的理解的改善。
Roughly 80% of ultraluminous infrared galaxies (ULIRGs) show blueshifted absorption in the resonance lines of neutral sodium, indicating that cool winds are common in such objects, as shown by Rupke et al. and by Martin. The neutral sodium (Na I) columns indicated by these absorption lines are ~1013-(3 × 1014) cm-2, a surprising result given that the bolometric luminosities range over a factor of only 4. We show that the gas in ULIRG outflows is likely to be in photoionization equilibrium. The very small ULIRG sample of Goldader et al. demonstrates that the ratio of UV flux to FIR flux varies by a factor ~100 from object to object. While the Goldader et al. sample does not overlap with those of Rupke et al. and Martin, we show that such a large variation in UV flux will produce a similar variation in the column of neutral sodium for a fixed mass flux and density. However, if the cold gas is in pressure equilibrium with a hot outflow with a mass-loss rate similar to the star formation rate, the range of ionization state is significantly smaller. Measurements of the UV flux for objects in the Martin and Rupke et al. catalogs will definitively determine whether photoionization effects are responsible for the wide variation seen in the sodium columns. If they are, a determination of the gas density and mass-loss rate in the cool winds will follow, with attendant improvements in our understanding of wind driving mechanisms and of the feedback effects of galaxies on their surroundings.