Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05
Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05
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DOI：
10.3847/2041-8213/ab5309
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发表时间：
2019-10
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通讯作者：
Yichen Zhang;Kei E. I. Tanaka;V. Rosero;J. Tan;J. Marvil;Yu Cheng;Mengyao Liu;M. Beltrán;G. Garay
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作者：
Yichen Zhang;Kei E. I. Tanaka;V. Rosero;J. Tan;J. Marvil;Yu Cheng;Mengyao Liu;M. Beltrán;G. Garay
大质量的原恒星产生强烈的辐射反馈，这可能有助于设定它们在吸积过程结束时达到的质量。因此，研究这种反馈对于理解大质量恒星的形成至关重要。我们利用阿塔卡马大型毫米/亚毫米阵列（阿尔马）在1.3毫米和卡尔G. Jansky甚大阵列（VLA）通过模拟自由-自由连续体，发现电离流出是一种光蒸发流，电子温度为10，000 K，中心电子数密度为1.5 × 107 cm−3，从半径为110 Au的圆盘发射。H30α氢复合线发射显示出强的脉泽放大，G45是极少数显示出这种毫米复合线脉泽的源之一。根据导出的电离光子速率，驱动源的质量估计为30-50 M <$，或根据H30α运动学，驱动源的质量估计为30-40 M <$。光蒸发材料的运动学主要由靠近盘平面的旋转控制，同时加速到盘平面上方的流出运动。光蒸发外流的质量损失率估计为100 ×（2-3.5）× 10−5 M yr−1。我们还发现了一个可能的射流嵌入在广角电离流出与非热发射的暗示。喷流和大量光蒸发外流的可能共存表明，尽管有强烈的光电离反馈，吸积仍在进行中。
Massive protostars generate strong radiation feedback, which may help set the mass that they achieve by the end of the accretion process. Studying such feedback is therefore crucial for understanding the formation of massive stars. We report the discovery of a photoionized bipolar outflow toward the massive protostar G45.47+0.05 using high-resolution observations at 1.3 mm with the Atacama Large Millimeter/Submillimeter Array (ALMA) and at 7 mm with the Karl G. Jansky Very Large Array (VLA). By modeling the free–free continuum, the ionized outflow is found to be a photoevaporation flow with an electron temperature of 10,000 K and an electron number density of ∼1.5 × 107 cm−3 at the center, launched from a disk of radius of 110 au. H30α hydrogen recombination line emission shows strong maser amplification, with G45 being one of very few sources to show such millimeter recombination line masers. The mass of the driving source is estimated to be 30–50 M⊙ based on the derived ionizing photon rate, or 30–40 M⊙ based on the H30α kinematics. The kinematics of the photoevaporated material is dominated by rotation close to the disk plane, while accelerated to outflowing motion above the disk plane. The mass loss rate of the photoevaporation outflow is estimated to be ∼(2–3.5) × 10−5 M⊙ yr−1. We also found hints of a possible jet embedded inside the wide-angle ionized outflow with nonthermal emissions. The possible coexistence of a jet and a massive photoevaporation outflow suggests that, in spite of the strong photoionization feedback, accretion is still ongoing.