Molecules with ALMA at Planet-forming Scales (MAPS). XII. Inferring the C/O and S/H Ratios in Protoplanetary Disks with Sulfur Molecules
Molecules with ALMA at Planet-forming Scales (MAPS). XII. Inferring the C/O and S/H Ratios in Protoplanetary Disks with Sulfur Molecules
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DOI：
10.3847/1538-4365/ac2583
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
R. Le Gal;K. Öberg;R. Teague;R. Loomis;C. Law;C. Walsh;E. Bergin;F. Ménard;D. Wilner;
中科院分区：
文献类型：
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作者：
R. Le Gal;K. Öberg;R. Teague;R. Loomis;C. Law;C. Walsh;E. Bergin;F. Ménard;D. Wilner;
含硫分子在生命前化学和行星可居住性中发挥着重要作用。它们也可作为化学年龄、元素碳氧比和谷物化学加工的探针。它们通常在包括太阳系在内的各种天体中检测到，但在行星形成盘中的分布和化学性质仍然是未知的。我们在阿尔马MAPS大型计划中对IM Lup，GM Aur，AS 209，HD 163296和MWC 480周围的五个盘进行了分辨率为100.“3的CS（2 - 1）观测。CS检测到在所有五个磁盘，显示各种径向强度分布和空间分布的样品，包括有趣的明显的方位角不对称性。对于MWC 480，我们提供了CS，13 CS，C34 S，H2 CS，OCS和SO2在0.05 ″的补充阿尔马观测。我们发现柱密度比N（H2 CS）/N（CS）= 1.2/3，表明盘中硫储层的相当大一部分是有机形式的（即，C x H y S z）。使用调整到MWC 480的天体化学盘模型，我们证明了N（CS）/N（SO）是一个很有前途的探针元素C/O比。与观测结果的比较提供了一个超太阳C/O。我们还发现了一个枯竭的气相S/H比，这表明要么硫储层的一部分被锁定在固相或它仍然在一个身份不明的气相储层。本文是《天体物理学杂志增刊》MAPS特刊的一部分。
Sulfur-bearing molecules play an important role in prebiotic chemistry and planet habitability. They are also proposed probes of chemical ages, elemental C/O ratio, and grain chemistry processing. Commonly detected in diverse astrophysical objects, including the solar system, their distribution and chemistry remain, however, largely unknown in planet-forming disks. We present CS (2 − 1) observations at ∼0.″3 resolution performed within the ALMA MAPS Large Program toward the five disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. CS is detected in all five disks, displaying a variety of radial intensity profiles and spatial distributions across the sample, including intriguing apparent azimuthal asymmetries. Transitions of C2S and SO were also serendipitously covered, but only upper limits are found. For MWC 480, we present complementary ALMA observations at ∼ 0.″5 of CS, 13CS, C34S, H2CS, OCS, and SO2. We find a column density ratio N(H2CS)/N(CS) ∼ 2/3, suggesting that a substantial part of the sulfur reservoir in disks is in organic form (i.e., C x H y S z ). Using astrochemical disk modeling tuned to MWC 480, we demonstrate that N(CS)/N(SO) is a promising probe for the elemental C/O ratio. The comparison with the observations provides a supersolar C/O. We also find a depleted gas-phase S/H ratio, suggesting either that part of the sulfur reservoir is locked in solid phase or that it remains in an unidentified gas-phase reservoir. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.