Extracting the Cold Neutral Medium from H i Emission with Deep Learning: Implications for Galactic Foregrounds at High Latitude
Extracting the Cold Neutral Medium from H i Emission with Deep Learning: Implications for Galactic Foregrounds at High Latitude
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DOI：
10.3847/1538-4357/aba19b
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发表时间：
2020-06
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影响因子：
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通讯作者：
C. Murray;Joshua E. G. Peek;Chang-Goo Kim
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作者：
C. Murray;Joshua E. G. Peek;Chang-Goo Kim
解析中性氢的相结构对于理解星际介质的生命周期是至关重要的。然而，H I温度和密度的准确测量受到测量H I吸收的背景连续源的可用性的限制。在这里，我们测试了深度学习在没有光学深度信息的大范围内提取HI属性的使用。我们使用ISM的三维数值模拟的综合观测来训练一维卷积神经网络，以预测冷中性介质(CNM)的分数()以及仅从21 cm发射对光学薄H I柱密度的光学深度()的修正。我们将我们的分析限制在高银河系纬度()，在那里谱线轮廓的复杂性被最小化。我们验证了网络的准确预测，并将结果与21厘米吸收的直接约束进行了比较。通过将该网络应用于GALFA-HI调查，我们生成了和的大面积地图。虽然总的贡献很小(∼5%)，但我们发现这些结构是普遍存在的。我们的结果与在21 cm发射中观察到的沿磁场方向的小尺度结构以CNM为主的图像是一致的。最后，我们证明了观测到的HI柱密度和尘埃变红()之间的相关性随着增加而下降，这表明未来利用HI来量化银河系前景的努力，即使在高纬度，也应该通过考虑HI相结构来提高保真度。
Resolving the phase structure of neutral hydrogen (H i) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of H i temperature and density are limited by the availability of background continuum sources for measuring H i absorption. Here we test the use of deep learning for extracting H i properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction ( ) of cold neutral medium (CNM) and the correction to the optically thin H i column density for optical depth ( ) from 21 cm emission alone. We restrict our analysis to high Galactic latitudes ( ), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts and by comparing the results with direct constraints from 21 cm absorption. By applying the network to the GALFA-H i survey, we generate large-area maps of and . Although the overall contribution to the total H i column of CNM-rich structures is small (∼5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21 cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between H i column density and dust reddening ( ) declines with increasing , indicating that future efforts to quantify foreground Galactic using H i, even at high latitudes, should increase fidelity by accounting for H i phase structure.