标题： 第一次极环分子气体的干涉观测：螺旋星系 NGC 2685 显示英文标题

标题： First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685

摘要： 我们利用奥雯谷射电天文台（OVRO）毫米波干涉仪，在NGC2685（螺旋星系）极环的西部和东部区域检测到四个巨大的分子云复合体（尺寸 < 6.6'' ~ 430 pc）。在极环中最亮的Hα和HI峰值附近发现了分子气体的辐射，并通过新的IRAM 30米单天线观测得到了确认。CO和HI谱线速度非常相似，提供了额外的动力学证据，表明CO发射来自极环。首次确定了极环内的总分子质量（使用银河标准转换因子，M_H2~(8-11)x10^6 M_sol）。利用单天线，我们在核区检测到约M_H2~4.4x10^6 M_sol的分子气体。从干涉数据得出的上限值较低（M_H2<0.7x10^6 M_sol），表明分子气体分布在延伸的（< 1.3 kpc）弥散盘中。这些新值比之前报告的低一个数量级。极环中的分子气体总量和原子气体含量与由小型富含气体天体的吸积形成一致，例如矮不规则星系。NGC2685系统的特性表明，极环和宿主星系已经稳定存在很长时间（几Gyr）。NGC2685盘内的第二（外）HI环很可能位于约11 kpc长恒星棒的外拉格朗日共振（OLR）处。 显示英文摘要

摘要： We have detected four Giant Molecular cloud Associations (GMAs) (sizes < 6.6'' ~ 430 pc) in the western and eastern region of the polar ring in NGC2685 (the Helix galaxy) using the Owens Valley Radio Observatory (OVRO) millimeter interferometer. Emission from molecular gas is found close to the brightest Halpha and HI peaks in the polar ring and is confirmed by new IRAM 30m single dish observations. The CO and HI 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_H2~(8-11)x10^6 M_sol, using the standard Galactic conversion factor). We detect about M_H2~4.4x10^6 M_sol in the nuclear region with the single dish. Our upper limit derived from the interferometric data is lower (M_H2<0.7x10^6 M_sol) 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 NGC2685 system suggest that the polar ring and the host galaxy have been in a stable configuration for a considerable time (few Gyr). The second (outer) HI ring within the disk of NGC2685 is very likely at the outer Lindblad resonance (OLR) of the ~ 11 kpc long stellar bar.