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arXiv 1802.04282astro-ph.GAastro-ph.SR
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向银河系隆起发射多环芳烃

Polycyclic aromatic hydrocarbon emission toward the Galactic bulge

Matthew J. Shannon, Els Peeters, Jan Cami, Joris A. D. L. Blommaert

摘要:

我们研究多环芳烃(PAH),尘埃和原子/分子发射朝向银河系的隆起使用斯皮策空间望远镜观测的四个领域:C32,C35,OGLE和NGC 6522。这些场分别近似地以(l,b)=(0.0°,1.0°)、(0.0°,-1.0°)、(0.4°,-2.1°)和(1.0°,-3.8°)为中心。远红外测光观测补充了斯皮策/IRS光谱数据,并用于构建光谱能量分布。我们发现C32和C35之间的尘埃和PAH排放总体上非常相似,部分原因是它们的位置-它们位于700万年前银河系外流事件的边界或附近,部分是冲击加热的。在C32和C35区域内,我们发现了一个Hα发射升高的区域,该区域与精细结构和[O IV]线发射升高以及PAH特征强度较弱相一致。我们很可能正在追踪外流进入新生环境的过渡区。在这些领域的多环芳烃丰度略低于典型的ISM值。在OGLE和NGC 6522领域,我们观察到的黄道尘为主的连续弱功能。SED拟合表明,在C32和C35的热尘埃颗粒具有可比的温度扩散,高纬度卷云。在C32和C35之间的多环芳烃属性中检测到的变异性很小,这表明多环芳烃的稳定种群占主导地位的整体光谱外观。事实上,它们的PAH特征与M82超级风非常相似,这表明我们正在探索当地的银河系风环境。

英文摘要:

We examine polycyclic aromatic hydrocarbon (PAH), dust and atomic/molecular emission toward the Galactic bulge using Spitzer Space Telescope observations of four fields: C32, C35, OGLE and NGC 6522. These fields are approximately centered on (l, b) = (0.0°, 1.0°), (0.0°, -1.0°), (0.4°, -2.1°) and (1.0°, -3.8°), respectively. Far-infrared photometric observations complement the Spitzer/IRS spectroscopic data and are used to construct spectral energy distributions. We find that the dust and PAH emission are exceptionally similar between C32 and C35 overall, in part explained due to their locations---they reside on or near boundaries of a 7 Myr-old Galactic outflow event and are partly shock-heated. Within the C32 and C35 fields, we identify a region of elevated Hα emission that is coincident with elevated fine-structure and [O IV] line emission and weak PAH feature strengths. We are likely tracing a transition zone of the outflow into the nascent environment. PAH abundances in these fields are slightly depressed relative to typical ISM values. In the OGLE and NGC 6522 fields, we observe weak features on a continuum dominated by zodiacal dust. SED fitting indicates that thermal dust grains in C32 and C35 have comparable temperatures to those of diffuse, high-latitude cirrus clouds. Little variability is detected in the PAH properties between C32 and C35, indicating that a stable population of PAHs dominates the overall spectral appearance. In fact, their PAH features are exceptionally similar to that of the M82 superwind, emphasizing that we are probing a local Galactic wind environment.

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