在模拟星云发射时对多成分尘埃衰减的需要：来自SDSS-IV MaNGA的限制
The need for multicomponent dust attenuation in modeling nebular emission: Constraints from SDSS-IV MaNGA
摘要：
几乎所有河外发射线研究都采用的一个基本假设是，不同发射线的衰减可以用一条衰减曲线来描述。在这里，我们表明这一假设在许多情况下失败的衍生结果的重要影响。我们发展了一种新的方法来测量三种跃迁之间的差异星云衰减：氢的巴耳末线，高电离跃迁，低电离跃迁。该方法将观测到的数据分箱在由衰减不敏感的线比所跨越的多维空间中。在每一个小的箱，线比的变化主要是由星云衰减的变化驱动。这使我们能够同时使用禁戒线和巴耳末线来测量星云的衰减。我们将这种方法应用于SDSS-IV MaNGA的240万个恒星形成spaxels样本。我们发现高电离线和巴耳末线的衰减可以用一条Fitzpatrick（1999）消光曲线和$R_V=3.1$很好地描述。然而，没有一个单一的衰减曲线可以同时考虑所有三个过渡。这强烈表明不同的谱线具有不同的有效衰减，可能是因为千秒差距分辨率的光谱混合了具有不同固有谱线比率和不同衰减水平的多个区域。因此，不同的线路遵循相同的衰减曲线的假设被打破。用Balmer线确定的单一衰减曲线来校正衰减敏感的禁线比，可能会使$A_V = 1$处由0.06- 0.25 dex导出的星云参数产生偏差，这取决于尘埃衰减模型的细节。具有高空间分辨率和大光谱覆盖范围的H II区域的统计大样本的观测对于改进建模和导出针对这种效应的精确校正是至关重要的。
英文摘要：
A fundamental assumption adopted in nearly every extragalactic emission-line study is that the attenuation of different emission lines can be described by a single attenuation curve. Here we show this assumption fails in many cases with important implications for derived results. We developed a new method to measure the differential nebular attenuation among three kinds of transitions: the Balmer lines of hydrogen, high-ionization transitions, and low-ionization transitions. This method bins the observed data in a multidimensional space spanned by attenuation-insensitive line ratios. Within each small bin, the variations in line ratios are mainly driven by the variations in the nebular attenuation. This allows us to measure the nebular attenuation using both forbidden lines and Balmer lines. We applied this method to a sample of 2.4 million star-forming spaxels from SDSS-IV MaNGA. We found that the attenuation of high ionization lines and Balmer lines can be well described by a single Fitzpatrick (1999) extinction curve with $R_V=3.1$. However, no single attenuation curve can simultaneously account for all three transitions. This strongly suggests that different lines have different effective attenuations, likely because spectroscopy at kiloparsec resolutions mixes multiple regions with different intrinsic line ratios and different levels of attenuation. As a result, the assumption that different lines follow the same attenuation curve breaks down. Using a single attenuation curve determined by Balmer lines to correct attenuation-sensitive forbidden line ratios could bias the nebular parameters derived by 0.06--0.25 dex at $A_V = 1$, depending on the details of the dust attenuation model. Observations of a statistically large sample of H II regions with high spatial resolutions and large spectral coverage are vital for improved modeling and deriving accurate corrections for this effect.
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