UNVEILING EXTRAGALACTIC STAR FORMATION USING RADIO RECOMBINATION LINES: AN EXPANDED VERY LARGE ARRAY PILOT STUDY WITH NGC 253
UNVEILING EXTRAGALACTIC STAR FORMATION USING RADIO RECOMBINATION LINES: AN EXPANDED VERY LARGE ARRAY PILOT STUDY WITH NGC 253
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使用无线电复合线揭开河外恒星形成的面纱：利用 NGC 253 进行扩展的超大型阵列试点研究
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发表时间：
2011
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通讯作者：
D. Pisano
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作者：
A. Kepley;L. Chomiuk;Kelsey E. Johnson;W. Goss;D. Balser;D. Pisano
无线电复合线(RRL)是对年轻恒星形成区域中的电离气体的强大的、无消光的诊断。不幸的是，这些线在外部星系中很难探测到。我们给出了对邻近的核星暴星系NGC253在33 GHz的RRL和射电连续辐射的扩展甚大阵列观测结果。我们探测了以前未观测到的H58α和H59αRRL，并同时对连续谱进行了灵敏的测量。我们测量了H58−和H59−的积分线通量分别为44.3±0.7W mα2和39.9±0.8W mα2。NGC253中的热气运动复杂，具有多个速度分量。我们把热气体密度限制在(1.4-4)×10~4 cm−~3，估算出电离光子通量为1×10~(53) S−~1。我们利用RRL运动学和所得到的电离光子通量证明NGC253的核区不受引力约束，这与从X射线和H-α测量得到的气体外流是一致的。H58α和H59α谱线的线型、通量和运动学与不同频率下的RRL的线型、通量和运动学一致，证实了之前更困难的高频观测的准确性。我们发现，对于河外RRL观测，EVLA的效率比超大阵列高一个数量级。这些观测既证明了EVLA的威力，也证明了利用EVLA进行河外RRL研究的未来潜力。
Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of Expanded Very Large Array (EVLA) observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nuclear starburst galaxy. We detect the previously unobserved H58α and H59α RRLs and make simultaneous sensitive measurements of the continuum. We measure integrated line fluxes of 44.3 ± 0.7 W m−2 and 39.9 ± 0.8 W m−2 for the H58α and H59α lines, respectively. The thermal gas in NGC 253 is kinematically complex with multiple velocity components. We constrain the density of the thermal gas to (1.4–4) × 104 cm−3 and estimate an ionizing photon flux of 1 × 1053 s−1. We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound, which is consistent with the outflow of gas inferred from the X-ray and Hα measurements. The line profiles, fluxes, and kinematics of the H58α and H59α lines agree with those of RRLs at different frequencies confirming the accuracy of the previous, more difficult, high-frequency observations. We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the Very Large Array. These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA.