A Centimeter-wave Study of Methanol and Ammonia Isotopologues in Sgr B2(N): Physical and Chemical Differentiation between Two Hot Cores
A Centimeter-wave Study of Methanol and Ammonia Isotopologues in Sgr B2(N): Physical and Chemical Differentiation between Two Hot Cores
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DOI：
10.3847/1538-4357/aaed3f
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发表时间：
2018-10
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影响因子：
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通讯作者：
E. Mills;J. Corby;A. R. Clements;N. Butterfield;P. Jones;M. Cunningham;J. Ott
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文献类型：
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作者：
E. Mills;J. Corby;A. R. Clements;N. Butterfield;P. Jones;M. Cunningham;J. Ott
我们给出了从氨的14NH3、15NH3和NH2D同位素以及甲醇的12CH3OH和13CH3OH同位素向SGR B2(N)发射的新的射频干涉图。在分辨率为∼3“(0.1pC)的情况下，我们能够在空间上分辨来自该源的两个热核的发射，并将其与该区域致密的HⅡ区的吸收分开。第一个(N1)是著名的v=kM S−1核，第二个(N2)是位于v=73 kM的6“核S−1。利用15NH3的发射和14NH3亚稳跃迁的超精细卫星，我们估计了这些源的14NH3柱密度，并与NH2D的结果进行了比较。我们发现，N_2的氨氚分数大约是N_1的10-20倍。我们还测量了氮气中的[15NH3/14NH3]丰度比，显然是氮气中的2-3倍，这可能表明氮气中的氮分馏程度相应更高。此外，我们还发现，N_2的甲醇丰度比N_1高7倍。综上所述，这些丰度特征表明，氮气是一个较年轻的来源，其低温下具有颗粒化学特征的物种目前正积极地从冰盖中解放出来，尚未在温暖的气相中达到化学平衡。在氮气中发现的高D丰度和可能的高15N丰度对于研究原始太阳系物质丰度的潜在星际来源是很有趣的。
We present new radio-frequency interferometric maps of emission from the 14NH3, 15NH3, and NH2D isotopologues of ammonia and the 12CH3OH and 13CH3OH isotopologues of methanol toward Sgr B2(N). With a resolution of ∼3″ (0.1 pc), we are able to spatially resolve emission from two hot cores in this source and separate it from absorption against the compact H ii regions in this area. The first (N1) is the well-known v = 64 km s−1 core, and the second (N2) is a core 6″ to the north at v = 73 km s−1. Using emission from 15NH3 and hyperfine satellites of 14NH3 metastable transitions, we estimate the 14NH3 column densities of these sources and compare them to those of NH2D. We find that the ammonia deuteration fraction of N2 is roughly 10–20 times higher than that in N1. We also measure an [15NH3/14NH3] abundance ratio that is apparently 2–3 times higher in N2 than in N1, which could indicate a correspondingly higher degree of nitrogen fractionation in N2. In addition, we find that N2 has a factor of 7 higher methanol abundance than N1. Together, these abundance signatures suggest that N2 is a younger source, for which species characteristic of grain chemistry at low temperatures are currently being actively liberated from ice mantles and have not yet reached chemical equilibrium in the warm gas phase. The high D abundance and possible high 15N abundance in NH3 found in N2 are interesting for studying the potential interstellar origin of abundances in primitive solar system material.