M83中的大尺度激波电离和光电离气体：恒星形成的影响
Large-scale shock-ionized and photo-ionized gas in M83: the impact of star formation
摘要：
利用哈勃空间望远镜（HST）第三代宽视场照相机（WFC 3）的窄带图像，利用谱线诊断图[O III]（5007 \degA）/Hβ vs. [S II]（6716 °A+6731 °A）/Hα研究了M83星云气体的电离结构.我们在逐像素（0.2”x 0.2”）的基础上生成诊断图，并将其与几种光电离和冲击电离模型进行比较。对于光电离气体，我们观察到log（[O III]/Hβ）比值从中心到旋臂逐渐增加，与金属丰度梯度一致，因为H II区域从中心向外从超级太阳丰度到大致太阳丰度。利用诊断图，我们将气体中的光电离成分与冲击电离成分分开。我们发现激波电离的Hα辐射占总辐射的2%到15-33%，这取决于所使用的分离标准。诊断图中一个有趣的特征是log（[O III]/Hβ）~ 0附近的水平分布。这一特征与2.0 Z \odot金属丰度和250 km/s至350 km/s范围内的冲击波速度的冲击电离模型很好地拟合。在外环与旋臂的边界上还检测到一个低速激波分量，其速度小于200 km/s，可能是由于：（1）附近的超新星遗迹;（2）外环与旋臂之间的动力学相互作用;目前的数据无法使我们区分这三种可能的解释。我们的主要结论是，即使在HST的分辨率，冲击气体代表总电离气体排放量的一小部分，在不到33%的总。然而，它实际上占了M83中心星暴产生的所有机械能。
英文摘要：
We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 \degA)/Hβ vs. [S II](6716 °A+6731 °A)/Hα with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.2" x 0.2") basis and compare it with several photo- and shock-ionization models. For the photo-ionized gas, we observe a gradual increase of the log([O III]/Hβ) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photo-ionized from the shock-ionized component of the gas. We find that the shock-ionized Hα emission ranges from ~2% to about 15-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is an horizontal distribution around log([O III]/Hβ) ~ 0. This feature is well fit by a shock-ionization model with 2.0 Z\odot metallicity and shock velocities in the range of 250 km/s to 350 km/s. A low velocity shock component, < 200 km/s, is also detected, and is spatially located at the boundary between the outer ring and the spiral arm. The low velocity shock component can be due to : 1) supernova remnants located nearby, 2) dynamical interaction between the outer ring and the spiral arm, 3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.
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