Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope
Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope
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DOI：
10.1086/523835
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发表时间：
2007-09
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影响因子：
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通讯作者：
J. Rho;T. Kozasa;W. Reach;J. Smith;L. Rudnick;T. DeLaney;J. Ennis;H. Gomez;A. Tappe;A. Tappe
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文献类型：
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作者：
J. Rho;T. Kozasa;W. Reach;J. Smith;L. Rudnick;T. DeLaney;J. Ennis;H. Gomez;A. Tappe;A. Tappe
我们进行了斯皮策红外光谱分析观测，几乎覆盖了仙后座A超新星遗迹的整个范围，每5“-10”产生一次中红外(5.5-35μm)光谱。Ar、Ne、O、Si、S、Fe和尘埃连续体的气线在大部分位置都很强。我们根据喷发尘埃的连续体形状识别出三种不同的喷发尘埃。主要的尘埃连续体形状在21μm处表现出一个强烈的峰值。从19-23μm范围产生的21μm峰值尘埃的无线图与[Ar II]、[O IV]和[Ne II]抛射线图非常相似，这意味着尘埃是在喷射物中新形成的。光谱拟合表明在这些区域中存在二氧化硅、镁原硅酸盐和FeO颗粒。第二类沙尘表现为持续上升至21μm，之后趋于平缓。这一“弱21μm”尘埃可能由Al_2O_3和C颗粒组成。第三种尘埃连续体形状没有什么特征，光谱平缓上升，很可能是由镁硅和Al_2O_3或Fe颗粒组成。对三个尘埃类别中的每一个使用质量最小的成分产生的总质量为0.020 M☉。使用最大质量的组合物产生的总质量为0.054 M☉。总尘埃质量的主要不确定性来自于选择适合无特征尘埃所需的尘埃成分以及70μm通量。从CaS A得到的新形成的尘埃质量足以解释高红移星系中尘埃质量的下限。
We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5-35 μm) spectra every 5″-10″. Gas lines of Ar, Ne, O, Si, S, and Fe, and dust continua were strong for most positions. We identify three distinct ejecta dust populations based on their continuum shapes. The dominant dust continuum shape exhibits a strong peak at 21 μm. A line-free map of 21 μm peak dust made from the 19-23 μm range closely resembles the [Ar II], [O IV], and [Ne II] ejecta-line maps, implying that dust is freshly formed in the ejecta. Spectral fitting implies the presence of SiO2, Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 μm and then flattens thereafter. This “weak 21 μm” dust is likely composed of Al2O3 and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO3 and either Al2O3 or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.020 M☉. Using the most massive composition yields a total mass of 0.054 M☉. The primary uncertainty in the total dust mass stems from the selection of the dust composition necessary for fitting the featureless dust as well as 70 μm flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to explain the lower limit on the dust masses in high-redshift galaxies.