H II Regions and Abundances in the “Dark Galaxy” DDO 154 and the Chemical Evolution of Dwarf Irregular Galaxies
H II Regions and Abundances in the “Dark Galaxy” DDO 154 and the Chemical Evolution of Dwarf Irregular Galaxies
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“暗星系”DDO 154 中的 H II 区域和丰度以及矮不规则星系的化学演化
DOI：
10.1086/319424
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
E. Skillman
中科院分区：
文献类型：
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作者：
Robert C. Kennicutt Jr.;E. Skillman
给出了低表面亮度矮不规则星系DDO 154的Hα成像和H II区的光学分光光度测量结果。该星系拥有一个非常小的人口微弱离散H II区域和较大的弥漫H II区域和电离壳。我们证实了货车Zee，Haynes和Salzer以前报道的非常低的星星形成率和极长的气体消耗时间。目前的星星形成速率比过去的平均速率低1.2 -4倍，证实了DDO 154先前被描述为一个“静止”的矮不规则星系。两个最亮的H II区域的分光光度法产生相对较低的氧丰度，为0.055 ± 0.008（O/H）Ω，与货车Zee等人先前的测定一致，并与先前确定的矮不规则星系的金属度-光度关系相一致。我们还发现N/O比为0.037 ± 0.003，略高于低金属丰度蓝色致密星系中的典型值0.025。虽然DDO 154被标记为“暗星系”，并且是具有大H I含量的低表面亮度星系的原型，但它的化学丰度与平均，低质量，矮不规则星系一致。假设中性气体是化学均匀的，我们得到一个有效的氧气产量约50%的太阳值，一个值，接近理论上有利于真正的氧气产量的值。因此，DDO 154可能几乎作为封闭系统发展。另一方面，如果扩展的H I盘中的丰度低于H II区域中的丰度，则有效产额的导出值被人为地夸大，并且DDO 154可能经历了金属富集气体的显著损失。
We present Hα imaging and optical spectrophotometry of H II regions in the low surface brightness dwarf irregular galaxy DDO 154. The galaxy possesses a very small population of faint discrete H II regions and larger diffuse H II regions and ionized shells. We confirm the very low star formation rate and extremely long gas consumption times reported previously by van Zee, Haynes, & Salzer. The current star formation rate is ∼2–4 times lower than its average past rate, confirming the previous characterization of DDO 154 as a "quiescent" dwarf irregular galaxy. Spectrophotometry of two of the brightest H II regions yields a relatively low oxygen abundance of 0.055 ± 0.008 (O/H)⊙, in agreement with the previous determination by van Zee et al., and in accordance with the previously determined metallicity-luminosity relationship for dwarf irregular galaxies. We also find an N/O ratio of 0.037 ± 0.003, which is marginally higher than the typical value of 0.025 found in low-metallicity blue compact galaxies. Although DDO 154 has been labeled "the dark galaxy" and is a prototype for low surface brightness galaxies with large H I content, its chemical abundances are consistent with an average, low-mass, dwarf irregular galaxy. Assuming that the neutral gas is chemically homogeneous, we derive an effective oxygen yield of roughly 50% of the solar value, a value that is close to the theoretically favored values for the true oxygen yield. Thus, it is possible that DDO 154 is evolving nearly as a closed system. On the other hand, if the abundances in the extended H I disk are lower than in the H II regions, the derived value of the effective yield has been artificially inflated, and DDO 154 may have experienced significant loss of metal-enriched gas.