HERSCHEL* FAR-INFRARED SPECTROSCOPY OF THE GALACTIC CENTER. HOT MOLECULAR GAS: SHOCKS VERSUS RADIATION NEAR Sgr A
HERSCHEL* FAR-INFRARED SPECTROSCOPY OF THE GALACTIC CENTER. HOT MOLECULAR GAS: SHOCKS VERSUS RADIATION NEAR Sgr A
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DOI：
10.1088/2041-8205/769/1/l13
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发表时间：
2013-05
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通讯作者：
J. Goicoechea;M. Etxaluze;J. Cernicharo;M. Gerin;D. Neufeld;A. Contursi;T. Bell;M. de Luca;P. Encrenaz;N. Indriolo;D. Lis;E. Polehampton;P. Sonnentrucker
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作者：
J. Goicoechea;M. Etxaluze;J. Cernicharo;M. Gerin;D. Neufeld;A. Contursi;T. Bell;M. de Luca;P. Encrenaz;N. Indriolo;D. Lis;E. Polehampton;P. Sonnentrucker
本文介绍了用Herschel星载PACS和SPIRE光谱仪对Sgr A* 进行的52-671 μm光谱扫描。实现的角分辨率使我们能够分离，第一次在远红外波长，发射到中央腔（气体在内部中央秒差距的星系）从周围的环核盘。朝向Sgr A* 的光谱主要是由来自中央星团的紫外光子照射的气体中产生的强[O iii]、[O i]、[C ii]、[N iii]、[N ii]和[C i]精细结构线（按光度递减顺序）所支配。此外，还探测到了~（12）CO（J = 4-3 ~ 24-23），~（13）CO，H_2O，OH，H_3O ~+，HCO ~+，HCN的旋转激发线，以及OH ~+，H_2O ~+，H_3O ~+，CH ~+，H_2O，OH，HF，CH，NH的基态吸收线。12 CO梯的激发与Tk = 103.1 K和n（H2）= 104 cm−3的热等温分量一致。这也与较高密度下的温度分量分布一致，其中大部分CO在Tk> 300 K。探测到的分子特征表明，目前，无论是非常增强的X射线还是宇宙射线通量在加热热分子气体方面都没有发挥主导作用。热的CO组分（取决于上述情况的CO柱的大部分或仅一小部分）由UV和冲击驱动加热的组合产生。如果辐射密集的团块/云不存在，冲击可能主导热分子气体的加热。这与朝向Sgr A* 检测到的高速气体一致。
We present a ∼52–671 μm spectral scan toward Sgr A* taken with the PACS and SPIRE spectrometers on board Herschel. The achieved angular resolution allows us to separate, for the first time at far-IR wavelengths, the emission toward the central cavity (gas in the inner central parsec of the galaxy) from that of the surrounding circumnuclear disk. The spectrum toward Sgr A* is dominated by strong [O iii], [O i], [C ii], [N iii], [N ii], and [C i] fine-structure lines (in decreasing order of luminosity) arising in gas irradiated by UV photons from the central stellar cluster. In addition, rotationally excited lines of 12CO (from J = 4–3 to 24–23), 13CO, H2O, OH, H3O+, HCO+, and HCN, as well as ground-state absorption lines of OH+, H2O+, H3O+, CH+, H2O, OH, HF, CH, and NH are detected. The excitation of the 12CO ladder is consistent with a hot isothermal component at Tk ≃ 103.1 K and n(H2) ≲ 104 cm−3. It is also consistent with a distribution of temperature components at higher density with most CO at Tk ≲ 300 K. The detected molecular features suggest that, at present, neither very enhanced X-ray nor cosmic-ray fluxes play a dominant role in the heating of the hot molecular gas. The hot CO component (either the bulk of the CO column or just a small fraction depending on the above scenario) results from a combination of UV- and shock-driven heating. If irradiated dense clumps/clouds do not exist, shocks likely dominate the heating of the hot molecular gas. This is consistent with the high-velocity gas detected toward Sgr A*.