ALFALFA DISCOVERY OF THE MOST METAL-POOR GAS-RICH GALAXY KNOWN: AGC 198691
ALFALFA DISCOVERY OF THE MOST METAL-POOR GAS-RICH GALAXY KNOWN: AGC 198691
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苜蓿发现已知最贫金属、富含气体的星系：AGC 198691
DOI：
10.3847/0004-637x/822/2/108
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
E. Aver
中科院分区：
文献类型：
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作者：
A. Hirschauer;J. Salzer;E. Skillman;D. Berg;K. McQuinn;J. Cannon;A. J. Gordon;M. Haynes;R. Giovanelli;E. Adams;S. Janowiecki;K. Rhode;R. Pogge;K. Croxall;E. Aver
我们展示了附近矮星系 AGC 198691 的光谱观测结果。该天体是极低质量矮星项目 Hi 巡天的一部分，该项目是对 Hi 质量在 106-107.2 M⊙ 范围内的星系的多波长研究，由阿雷西博传统快速 ALFA (ALFALFA) 巡天发现。我们使用 Mayall 4 m 上的新型高通量 KPNO 俄亥俄州立多目标摄谱仪以及 MMT 6.5 m 望远镜上的蓝色通道摄谱仪获得了 AGC 198691 中孤单 H ii 区域的光谱。这些观测结果使得能够测量温度敏感的[O iii]λ4363线，从而确定AGC 198691的“直接”氧丰度。我们发现该系统是一个极度缺金属（XMD）系统，氧丰度为12+log(O/H) = 7.02 ± 0.03，使AGC 198691成为当地宇宙中已知丰度最低的恒星形成星系。已知的五个丰度最低的星系中的两个是由 ALFALFA 盲 H i 巡天发现的；这种高产量的 XMD 星系代表了寻找金属极其贫乏的星系的范式转变。
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H i in Extremely Low-Mass Dwarfs project, which is a multi-wavelength study of galaxies with H i masses in the range of 106–107.2 M⊙, discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We have obtained spectra of the lone H ii region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph on the Mayall 4 m, as well as with the Blue Channel spectrograph on the MMT 6.5 m telescope. These observations enable the measurement of the temperature-sensitive [O iii]λ4363 line and hence the determination of a “direct” oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 ± 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind H i survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.