EVIDENCE FOR CO SHOCK EXCITATION IN NGC 6240 FROM HERSCHEL SPIRE SPECTROSCOPY-猫眼课题宝

DOI：

10.1088/2041-8205/762/2/l16

发表时间：

2012-11

期刊：

The Astrophysical Journal Letters

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

R. Meijerink;R. Meijerink;L. Kristensen;A. Weiss;P. V. D. Werf;F. Walter;M. Spaans;A. F. Loenen;J. Fischer;F. Israel;K. Isaak;P. Papadopoulos;S. Aalto;L. Armus;V. Charmandaris;K. Dasyra;T. Díaz-Santos;A. Evans;A. Evans;Yu Gao;E. González-Alfonso;R. Güsten;Christian Henkel;C. Henkel;C. Kramer;S. Lord;J. Martín-Pintado;D. Naylor;D. Sanders;Howard A. Smith;L. Spinoglio;G. Stacey;S. Veilleux;M. Wiedner

我们给出了附近发光红外星系NGC 6240的赫歇尔尖塔FTS光谱。共检测到20条线，包括CO J = 4−3 ~ J = 13−12,6条H2O旋转线，[C i]和[N ii]精细结构线。NGC 6240的CO与连续光谱的光度比是Mrk 231的10倍。虽然NGC 6240和Mrk 231的CO阶梯非常相似，但紫外线和/或x射线照射不太可能是NGC 6240中气体激发的原因。我们将C和J激波模型应用于H2 v = 1 - 0 S(1)和v = 2-1 S(1)线和CO旋转梯。用冲击速度vs = 10 km s−1和预冲击密度nH = 5 × 104 cm−3的模型可以最好地再现CO阶梯。我们发现最适合H2线的解是简并的。激波速度和数量密度分别在vs = 17-47 km s−1和nH = 107-5 × 104 cm−3之间。因此，H2谱线需要比CO谱线更强大的激波。我们推断，大多数气体目前被缓慢（10 km s−1）激波适度搅动，而只有一小部分星际介质（约1%）暴露在高速激波中。这意味着气体正在迅速失去其高度湍流运动。我们认为，高CO线连续比是一个关键的诊断冲击的存在。

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 H2O 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 H2 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 vs = 10 km s−1 and a pre-shock density nH = 5 × 104 cm−3. We find that the solution best fitting the H2 lines is degenerate. The shock velocities and number densities range between vs = 17–47 km s−1 and nH = 107–5 × 104 cm−3, respectively. The H2 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.

EVIDENCE FOR CO SHOCK EXCITATION IN NGC 6240 FROM HERSCHEL SPIRE SPECTROSCOPY

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