蓝色致密矮星系中性气体的金属富集：Pox 36的令人信服的例子
Metal enrichment of the neutral gas of blue compact dwarf galaxies: the compelling case of Pox 36
摘要：
我们用远紫外光谱探测器（FUSE）分析了Pox 36的星际光谱。选择Pox 36是因为前景气体含量相对较低，这使得有可能检测到足够弱的吸收线，使得看不见的成分不应该饱和。探测到HI、NI、OI、SiII、PII、ArI和FeII的星际谱线。柱密度直接从观测到的线轮廓，除了HI，其线被恒星吸收污染。我们使用TLUSTY模型来去除恒星连续体并隔离星际分量。最佳拟合表明，占主导地位的恒星星族是B 0。星际HI线的拟合给出了10^{20.3 \pm 0.4} cm-2的柱密度。化学丰度，然后计算从柱密度使用的主要电离阶段的中性气体。我们的丰度相比，从发射线光谱中的光学测量。我们的研究结果表明，中性气体的Pox 36是金属缺乏的一个因素~7相比，电离气体，他们同意的金属丰度~1/35 Z $_\odot$。结论：中性相和电离相之间的丰度不连续性意味着，连续的恒星形成事件释放的大部分金属与HI气体混合。富集的体积范围如此之大，以至于中性气体的金属丰度仅略有增加。恒星形成区只能富集一小部分（~1%），但它会大大提高其金属丰度。我们的结果进行了比较，与其他BCD。我们确认了中性气体中金属的总体丰度不足，也许只有金属丰度最低的BCD没有显示出不连续性。
英文摘要：
We present the analysis of the interstellar spectrum of Pox 36 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Pox 36 was selected because of the relatively low foreground gas content that makes it possible to detect absorption-lines weak enough that unseen components should not be saturated. Interstellar lines of HI, NI, OI, SiII, PII, ArI, and FeII are detected. Column densities are derived directly from the observed line profiles except for HI, whose lines are contaminated by stellar absorption. We used the TLUSTY models to remove the stellar continuum and isolate the interstellar component. The best fit indicates that the dominant stellar population is B0. The fit of the interstellar HI line gives a column density of 10^{20.3\pm0.4} cm-2. Chemical abundances were then computed from the column densities using the dominant ionization stage in the neutral gas. Our abundances are compared to those measured from emission-line spectra in the optical. Our results suggest that the neutral gas of Pox 36 is metal-deficient by a factor ~7 as compared to the ionized gas, and they agree with a metallicity of ~1/35 Z$_\odot$. Conclusions: The abundance discontinuity between the neutral and ionized phases implies that most of the metals released by consecutive star-formation episodes mixes with the HI gas. The volume extent of the enrichment is so large that the metallicity of the neutral gas increases only slightly. The star-forming regions could be enriched only by a small fraction (~1%), but it would greatly enhance its metallicity. Our results are compared to those of other BCDs. We confirm the overall underabundance of metals in their neutral gas, with perhaps only the lowest metallicity BCDs showing no discontinuity.
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