Dense and Warm Molecular Gas between Double Nuclei of the Luminous Infrared Galaxy NGC 6240
Dense and Warm Molecular Gas between Double Nuclei of the Luminous Infrared Galaxy NGC 6240
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DOI：
10.1093/pasj/57.4.575
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发表时间：
2005-07
影响因子：
2.3
通讯作者：
K. Nakanishi;S. Okumura;K. Kohno;R. Kawabe;T. Nakagawa
中科院分区：
文献类型：
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作者：
K. Nakanishi;S. Okumura;K. Kohno;R. Kawabe;T. Nakagawa
利用Nobeama毫米波阵列和彩虹干涉仪对发光红外合并星NGC6240的12Co(1-0)、HCN(1-0)、Hco+(1-0)和13Co(1-0)分子谱线进行了高空间分辨率的观测。所有观测到的分子发射线都集中在星系双核之间的区域。但与12Co相比，HcN和HcO+的排放分布更紧密，与恒星形成区不一致。HCN/12Co谱线强度比为0.25，这表明双核之间的分子气大部分是致密的。将观测到的高HCN/13CO强度比5.9与大速度梯度计算的结果进行了比较，结果表明分子气是致密的[n(H_2)=10^{4-6}cm^-3]和热的(T_kin>；50K)。NGC6240中观测到的结构可以用分子气体和恒星形成的时间演化来解释，这种演化是由两个星系核几乎迎头相撞或非常近地相遇并伴随着致密气体和恒星形成区而引起的。
High spatial resolution observations of the 12CO(1-0), HCN(1-0), HCO+(1-0), and 13CO(1-0) molecular lines toward the luminous infrared merger NGC 6240 have been performed using the Nobeyama Millimeter Array and the RAINBOW Interferometer. All of the observed molecular emission lines are concentrated in the region between the double nuclei of the galaxy. However, the distributions of both HCN and HCO+ emissions are more compact compared with that of 12CO, and they are not coincident with the star-forming regions. The HCN/12CO line intensity ratio is 0.25; this suggests that most of the molecular gas between the double nuclei is dense. A comparison of the observed high HCN/13CO intensity ratio, 5.9, with large velocity gradient calculations suggests that the molecular gas is dense [n(H_2)=10^{4-6} cm^-3] and warm (T_kin>50 K). The observed structure in NGC 6240 may be explained by time evolution of the molecular gas and star formation, which was induced by an almost head-on collision or very close encounter of the two galactic nuclei accompanied with the dense gas and star-forming regions.