Spatially resolved Spitzer-IRS spectral maps of the superwind in M82
Spatially resolved Spitzer-IRS spectral maps of the superwind in M82
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DOI：
10.1093/mnras/stv1101
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发表时间：
2015-05
影响因子：
4.8
通讯作者：
P. Beirão;L. Armus;M. Lehnert;P. Guillard;P. Guillard;T. Heckman;B. Draine;D. Hollenbach;F. Walter;K. Sheth;John-David T. Smith;P. Shopbell;F. Boulanger;J. Surace;C. Hoopes;C. Engelbracht
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文献类型：
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作者：
P. Beirão;L. Armus;M. Lehnert;P. Guillard;P. Guillard;T. Heckman;B. Draine;D. Hollenbach;F. Walter;K. Sheth;John-David T. Smith;P. Shopbell;F. Boulanger;J. Surace;C. Hoopes;C. Engelbracht
我们已经用斯皮策−红外光谱绘制了附近星暴星系M82在中红外波段的超风/晕区。所覆盖的光谱区域包括H_2 S(1)-S(3)、[Ne II]、[Ne III]发射线和多环芳烃特征。我们估计出的热分子气体的总热H2质量和动能介于M_(Wain)∼5和17×10~(^6)M_⊙和E_K∼6和20×10~(^(53)erg)之间。利用红外光谱中6.2、7.7和11.3μm多环芳烃特征的比值，我们能够估计超风中小颗粒的平均尺寸和电离态。在整个流出过程中，PAH通量比有很大的变化。在整个风区，11.3/7.7和6.2/7.7的PAH比率的变化都超过了5倍。北风有大量的多环芳烃，其比值为6.2/7.7，比星爆盘和南风都小，这表明平均而言，多环芳烃的排放源更大，电离度更高。热分子气体/PAH通量比(H_2/PAH)在流出时比星暴盘提高了10-100倍。H_2/PAH比的这种增强似乎并不是伴随着流出的原子气体的电离(用[Ne III]/[Ne II]线通量比测量的)。这表明，外流中的大部分暖H_2是由激波激发的。观测到的H2谱线强度可以用低速激波(v<；40公里S^(−1))驱动成携带在外流中的中等密度分子气体(10^2<；n_H<；10^4 cm^(−3))来再现。
We have mapped the superwind/halo region of the nearby starburst galaxy M82 in the mid-infrared with Spitzer − IRS. The spectral regions covered include the H_2 S(1)–S(3), [Ne II], [Ne III] emission lines and polycyclic aromatic hydrocarbon (PAH) features. We estimate the total warm H2 mass and the kinetic energy of the outflowing warm molecular gas to be between M_(warm) ∼ 5 and 17 × 10^6 M_⊙ and E_K ∼ 6 and 20 × 10^(53) erg. Using the ratios of the 6.2, 7.7 and 11.3 μm PAH features in the IRS spectra, we are able to estimate the average size and ionization state of the small grains in the superwind. There are large variations in the PAH flux ratios throughout the outflow. The 11.3/7.7 and the 6.2/7.7 PAH ratios both vary by more than a factor of 5 across the wind region. The northern part of the wind has a significant population of PAH's with smaller 6.2/7.7 ratios than either the starburst disc or the southern wind, indicating that on average, PAH emitters are larger and more ionized. The warm molecular gas to PAH flux ratios (H_2/PAH) are enhanced in the outflow by factors of 10–100 as compared to the starburst disc. This enhancement in the H_2/PAH ratio does not seem to follow the ionization of the atomic gas (as measured with the [Ne III]/[Ne II] line flux ratio) in the outflow. This suggests that much of the warm H_2 in the outflow is excited by shocks. The observed H_2 line intensities can be reproduced with low-velocity shocks (v < 40 km s^(−1)) driven into moderately dense molecular gas (10^2 < n_H < 10^4 cm^(−3)) entrained in the outflow.