arXiv 2209.033672022-09-07astro-ph.EPastro-ph.SR

原行星盘中线压展宽和气体面密度直接约束的发现

Discovery of Line Pressure Broadening and Direct Constraint on Gas Surface Density in a Protoplanetary Disk

Tomohiro C. Yoshida, Hideko Nomura, Takashi Tsukagoshi, Kenji Furuya, Takahiro Ueda

备注：: 12 pages, 5 figures, accepted for publication in ApJL
DOI：: 10.3847/2041-8213/ac903a

摘要：

原行星盘的气体表面密度分布是了解行星形成的最基本的物理性质之一。然而，它是具有挑战性的，以确定表面密度分布的观测，因为H $_2$发射不能观察到在低温区。我们分析了阿塔卡马大型毫米/亚毫米阵列（ALMA）的\co线对TW Hya周围的原行星盘的档案数据，并发现了由于压力加宽而产生的极宽的线翼。结合以前报道的光学薄CO同位素线，压力加宽线翼使我们能够直接确定中平面气体密度的第一次。在$\sim5$ au中心恒星的气体表面密度达到$\sim 10^3\ {\rm g\ cm^{-2}}$，这表明盘的内部区域有足够的质量形成一颗质量为600亿的行星。另外，与腔外部相比，气体表面密度在内腔处下降$\sim2$数量级。我们还发现了一个低CO丰度的$\sim 10^{-6}$相对于H $_2$，即使在CO雪线，这表明CO的转化为挥发性较低的物种。结合我们的结果和以前的研究，气体表面密度在$r\sim 20$ au处发生跳跃，表明内部区域（$3<r<20$ au）可能是磁旋转不稳定死区。这项研究揭示了直接气体表面密度约束，而不假设CO/H $_2$比使用ALMA。

英文摘要：

The gas surface density profile of protoplanetary disks is one of the most fundamental physical properties to understand planet formation. However, it is challenging to determine the surface density profile observationally, because the H$_2$ emission cannot be observed in low-temperature regions. We analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) archival data of the \co line toward the protoplanetary disk around TW Hya and discovered extremely broad line wings due to the pressure broadening. In conjunction with a previously reported optically thin CO isotopologue line, the pressure broadened line wings enabled us to directly determine the midplane gas density for the first time. The gas surface density at $\sim5$ au from the central star reaches $\sim 10^3\ {\rm g\ cm^{-2}}$, which suggests that the inner region of the disk has enough mass to form a Jupiter-mass planet. Additionally, the gas surface density drops at the inner cavity by $\sim2$ orders of magnitude compared to outside the cavity. We also found a low CO abundance of $\sim 10^{-6}$ with respect to H$_2$, even inside the CO snowline, which suggests conversion of CO to less volatile species. Combining our results with previous studies, the gas surface density jumps at $r\sim 20$ au, suggesting that the inner region ($3<r<20$ au) might be the magnetorotational instability dead zone. This study sheds light on direct gas-surface-density constraint without assuming the CO/H$_2$ ratio using ALMA.

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英文摘要：

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