First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685
First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685
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极环中分子气体的首次干涉观测：螺旋星系 NGC 2685
DOI：
10.1086/344242
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
N. Scoville
中科院分区：
文献类型：
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作者：
E. Schinnerer;N. Scoville
我们利用欧文斯谷射电天文台毫米波干涉仪在NGC 2685（赫敏星系）极环的西部和东部区域探测到了4个巨大的分子云星协（大小≤6.″6 × 430 pc）。来自分子气体的发射被发现接近极环中最亮的Hα和H I峰，并被新的IRAM 30 m单碟观测所证实。CO和H I线速度是非常相似的，提供额外的运动学确认，CO排放出现从极环。首次测定了极环的总分子质量[M ~（8-11）× 106 M]。我们用单碟法在核区探测到约4.4 × 106 M的裂变。由干涉数据得到的上限较低（M ≤ 0.7 × 106 M），表明分子气体分布在一个扩展的（≥ 1.3kpc）扩散盘中。这些新的数值比以前报告中的数值低一个数量级。分子气体的总量和极环的原子气体含量与小型富含气体的天体（如矮不规则星）的吸积形成一致。NGC 2685系统的性质表明，极环和宿主星系已经在相当长的时间（几千兆年）内处于稳定的配置。NGC 2685的第二个（外）H I环很可能位于~11 kpc长的恒星棒的林德布拉德共振处。
We have detected four giant molecular cloud associations (sizes ≤6.″6 ≈ 430 pc) in the western and eastern regions of the polar ring in NGC 2685 (the Helix galaxy) using the Owens Valley Radio Observatory millimeter interferometer. Emission from molecular gas is found close to the brightest Hα and H I peaks in the polar ring and is confirmed by new IRAM 30 m single-dish observations. The CO and H I line velocities are very similar, providing additional kinematic confirmation that the CO emission emerges from the polar ring. For the first time, the total molecular mass within a polar ring is determined [M ~ (8-11) × 106 M☉, using the standard Galactic conversion factor]. We detect about M ~ 4.4 × 106 M☉ in the nuclear region with the single dish. Our upper limit derived from the interferometric data is lower (M ≤ 0.7 × 106 M☉), suggesting that the molecular gas is distributed in an extended (≥1.3 kpc) diffuse disk. These new values are an order of magnitude lower than in previous reports. The total amount of molecular gas and the atomic gas content of the polar ring are consistent with formation due to accretion of a small gas-rich object, such as a dwarf irregular. The properties of the NGC 2685 system suggest that the polar ring and the host galaxy have been in a stable configuration for a considerable time (a few gigayears). The second (outer) H I ring within the disk of NGC 2685 is very likely at the outer Lindblad resonance of the ~11 kpc long stellar bar.