用阿塔卡马大型毫米/亚毫米阵列直接探测由引力不稳定性形成的气体巨星的前兆
Direct detection of precursors of gas giants formed by gravitational instability with the Atacama Large Millimetre/sub-millimetre Array
摘要：
引力不稳定的阶段预计在盘演化的早期阶段，当盘的质量仍然是恒星质量的一个重要部分。星盘碎裂成亚恒星物体可能发生在星盘寒冷的外部。直接探测到大量的气体团块在坍缩成气体巨行星的过程中，将为磁盘不稳定性模型提供前所未有的测试。在这里，我们使用最先进的3D辐射水模拟磁盘进行碎片成大规模的气体巨星，后处理的RADMC-3D射线追踪代码，以产生尘埃连续发射图。然后将这些数据输入到通用天文学软件应用程序（CASA）ALMA模拟器中。合成图显示，在距离蛇夫座恒星形成区（125 pc）的完整配置中，阿塔卡马大型毫米/亚毫米阵列（ALMA）可以检测到过度密集的螺旋臂和不同坍缩阶段的实际团块。团块的检测在较短的波长（690 GHz）下特别有效，结合了两种分辨率和多尺度清洁。此外，我们表明，一个基于通量的估计质量的原行星团可以从可比的3倍以上的重力约束的团块质量。估计的质量取决于假设的不透明度和气体温度，这应该使用辐射-水力模拟的输入来设置。我们的结论是，ALMA有能力检测“吸烟枪”系统，是一个路标的磁盘不稳定模型的气体巨行星形成。
英文摘要：
Phases of gravitational instability are expected in the early phases of disk evolution, when the disk mass is still a substantial fraction of the mass of the star. Disk fragmentation into sub-stellar objects could occur in the cold exterior part of the disk. Direct detection of massive gaseous clumps on their way to collapse into gas giant planets would offer an unprecedented test of the disk instability model. Here we use state-of-the-art 3D radiation-hydro simulations of disks undergoing fragmentation into massive gas giants, post-processed with the RADMC-3D ray-tracing code to produce dust continuum emission maps. These are then fed into the Common Astronomy Software Applications (CASA) ALMA simulator. The synthetic maps show that both overdense spiral arms and actual clumps at different stages of collapse can be detected with the Atacama Large Millimetre/sub-millimetre Array (ALMA) in the full configuration at the distance of the Ophiuchus star forming region (125 pc). The detection of clumps is particularly effective at shorter wavelengths (690 GHz) combining two resolutions with multi-scale clean. Furthermore, we show that a flux-based estimate of the mass of a protoplanetary clump can be from comparable to a factor of 3 higher than the gravitationally bound clump mass. The estimated mass depends on the assumed opacity, and on the gas temperature, which should be set using the input of radiation-hydro simulations. We conclude that ALMA has the capability to detect "smoking gun" systems that are a signpost of the disk instability model for gas giant planet formation.
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