来自合成恒星形成区的见解：II。用改进的黑体拟合法测量粉尘表面密度、温度和气体质量
Insights from Synthetic Star-forming Regions: II. Verifying Dust Surface Density, Dust Temperature & Gas Mass Measurements with Modified Blackbody Fitting
摘要：
我们使用一个大的数据集的现实合成观测（PaperI），以评估观测技术如何影响恒星形成区域的物理性质的测量。在本文中（纸II），我们探讨了测量的总气体质量，尘埃表面密度和尘埃温度图的可靠性来自合成赫歇尔观测的改进黑体拟合。通过对测量的尘埃表面密度和尘埃温度的逐像素分析，我们发现了一个令人担忧的误差，特别是在靠近恒星形成地点和低密度区域的地方，对于那些“污染”的像素，表面密度可以被低估/高估高达三个数量级。有鉴于此，我们建议在恒星形成活跃的地区谨慎对待这项技术的像素结果。在银河系内面典型的高背景区域中，我们无法恢复单个合成区域的可靠表面密度图，因为低质量区域在FIR背景中丢失。当测量中等背景区域的总气体质量时，我们发现改进的黑体拟合在10 kpc的距离内工作良好（绝对误差：+9%;-13%）（误差随距离增加）。通常，初始图像被卷积到最大的公共波束尺寸，这在大面积上涂抹污染像素。由此产生的信息损失使得这种常用的技术不太可验证，因为现在卡方值不能用作拟合像素的质量指标。我们对总气体质量的控制测量（没有卷积到最大公共光束尺寸的步骤）产生类似的结果（绝对误差：+20%;-7%），同时具有低得多的中值误差，特别是对于大质量恒星反馈相位。在即将发表的论文（III和IV）中，我们用直接和间接技术测试了测量的恒星形成率的可靠性。
英文摘要：
We use a large data-set of realistic synthetic observations (PaperI) to assess how observational techniques affect the measurement of physical properties of star-forming regions. In this paper (PaperII), we explore the reliability of the measured total gas mass, dust surface density and dust temperature maps derived from modified blackbody fitting of synthetic Herschel observations. We found from our pixel-by-pixel analysis of the measured dust surface density and dust temperature a worrisome error spread especially close to star-formation sites and low-density regions, where for those "contaminated" pixels the surface densities can be under/overestimated by up to three orders of magnitude. In light of this, we recommend to treat the pixel-based results from this technique with caution in regions with active star formation. In regions of high background typical in the inner Galactic plane, we are not able to recover reliable surface density maps of individual synthetic regions, since low-mass regions are lost in the FIR background. When measuring the total gas mass of regions in moderate background, we find that modified blackbody fitting works well (absolute error:+9%;-13%) up to 10kpc distance (errors increase with distance). Commonly, the initial images are convolved to the largest common beam-size, which smears contaminated pixels over large areas. The resulting information loss makes this commonly-used technique less verifiable as now chi^2-values cannot be used as a quality indicator of a fitted pixel. Our control measurements of the total gas mass (without the step of convolution to the largest common beam size) produce similar results (absolute error:+20%;-7%) while having much lower median errors especially for the high-mass stellar feedback phase. In upcoming papers (III&IV) we test the reliability of measured star-formation rate with direct and indirect techniques.
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