The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
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银河中心分子云的热状态：非光子驱动加热的证据
DOI：
10.1051/0004-6361/201220096
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发表时间：
2013-02-01
影响因子：
6.5
通讯作者：
Mangum, J.
中科院分区：
文献类型：
--
作者：
Ao, Y.;Henkel, C.;Mangum, J.
我们利用阿塔卡马探路者实验（APEX）12 m望远镜在218 GHz同时观测了para-H2 CO的J（KAKc）= 3（03）-> 2（02），3（22）-> 2（21）和3（21）-> 2（20）跃迁，以确定银河系中心分子区（CMZ）致密气体的动力学温度。这张地图沿着沿着银河平面延伸了大约40' x 8'（类似于100 x 20 pc（2）），线性分辨率为1. 2 pc。发现三条谱线中最强的H2 CO（3（03）-> 2（02））跃迁是广泛的，并且其发射显示出与氨类似的空间分布。对-H2 CO的相对丰度为0.5 - 1.2 × 10 ~（-9），这与低频H2 CO吸收线的结果一致。导出的单个分子云的气体动力学温度范围从50 K到超过100 K的值。虽然没有发现一个系统的趋势（降低）的动力学温度与（增加）的角距离从银河系中心（GC），云的最高温度（T-kin > 100 K）都位于核附近。对于密云外的分子气体，平均动力学温度为65 +/- 10 K。GC区域大尺度分子云的高温可能是由湍流能量耗散和/或宇宙射线而不是光子驱动的。分子气体的这种非光子驱动的热态，为在超亮红外星系（ULIRGs）中发现的更遥远的剧烈恒星爆发提供了一个很好的模板。
We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J(KAKc) = 3(03) -> 2(02), 3(22) -> 2(21), and 3(21) -> 2(20) transitions of para-H2CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40' x 8' (similar to 100 x 20 pc(2)) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H2CO (3(03) -> 2(02)) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H2CO is 0.5 - 1.2 x 10(-9), which is consistent with results from lower frequency H2CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T-kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65 +/- 10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and / or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).