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首页> 外文期刊>The Astrophysical Journal. Letters >Evidence for CO shock excitation in NGC 6240 from Herschel Spire spectroscopy
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Evidence for CO shock excitation in NGC 6240 from Herschel Spire spectroscopy

机译：赫歇尔螺旋光谱法在NGC 6240中激发CO激波的证据

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摘要

We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J = 4-3 through J = 13-12, 6 H_2O rotational lines, and [C I] and [N II] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H_2 v = 1-0 S(1) and v = 2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s = 10 km s ~(-1) and a pre-shock density n_H = 5 × 10~4 cm~(-3). We find that the solution best fitting the H_2 lines is degenerate. The shock velocities and number densities range between v _s = 17-47 km s~(-1) and n_H = 10~7-5 × 10~4 cm~(-3), respectively. The H_2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s~(-1)) shocks while only a small fraction (? 1%) of the interstellar medium is exposed to the high-velocity shocks. This implies that the gas is rapidly losing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
机译：我们介绍了附近的发光红外星系NGC 6240的Herschel SPIRE FTS光谱。总共检测到20条线，包括CO J = 4-3至J = 13-12、6条H_2O旋转线以及[CI]和[N II]细线。在NGC 6240中，CO与连续体的光度比是Mrk 231的10倍。尽管NGC 6240和Mrk 231的CO阶梯非常相似，但紫外线和/或X射线辐照不太可能引起气体的激发在NGC 6240中。我们对H_2 v = 1-0 S（1）和v = 2-1 S（1）线和CO旋转阶梯应用了C和J冲击模型。 CO梯形图最好由冲击速度v_s = 10 km s〜（-1）和震前密度n_H = 5×10〜4 cm〜（-3）的模型重现。我们发现最适合H_2线的解决方案是退化的。冲击速度和数量密度分别在v_s = 17-47 km s〜（-1）和n_H = 10〜7-5×10〜4 cm〜（-3）之间。因此，H_2线比CO线需要强大得多的冲击力。我们推断，目前大多数气体在缓慢的（10 km s〜（-1））冲击中被适度地搅动，而星际介质中只有一小部分（？1％）受到高速冲击。这意味着气体正在迅速失去其高度湍流的运动。我们认为，高CO线与连续谱之比是诊断电击的关键诊断。

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