A Near-Infrared Survey of Radio-selected Ultracompact H II Regions
A Near-Infrared Survey of Radio-selected Ultracompact H II Regions
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射电选择超紧凑 H II 区域的近红外探测
DOI：
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发表时间：
2002
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通讯作者：
G. Rieke
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作者：
Margaret M. Hanson;K. Luhman;G. Rieke
对代表47个不同恒星形成地点的63个无线电选择的超紧凑（UC）H II区域的近红外（NIR）测量已经完成。该调查是使用H波段成像和中等分辨率，R = 1200，K波段光谱，集中在UC H II地区的无线电发射峰。这项调查的目的是确定无线电选择UC H II区域的分数，可以用近红外观测和分析进行研究。在63个无线电选择的UC H II区域中，大约50%似乎在溴γ发射的近红外波长处被检测到（107尔格s-1 cm-2 Sr-1）。针对检测到的UC H II区域的典型视线消光范围为AV = 30至50，尽管测量到一个源的AV = 80。对于这些UC H II区域中的一些区域，通过光球跃迁的高信噪比NIR光谱检测到中心电离源。这个初步调查表明，也许5%-10%的UC H II区域显示近红外对应物将有直接可检测的中央电离源。利用He I 2.11与Brγ的比值，估算了25个UC H II区中心电离星的有效温度。虽然He I并不总是在UC H II区域被检测到，但当它被发现或确定了一个有意义的上限时，He I 2.11与Brγ之比所暗示的光谱类型与来自射电的光谱类型的类似估计非常匹配。基于中红外测量的模型预测似乎低估了我们直接检测光谱类型的中央电离星的温度。在我们的UC H II区域样本中，H2 2-1 S（1）和1-0 S（0）相对于1-0 S（1）线的线比通常指示密集的光解离区域，而不是冲击，类似于在猎户座棒中看到的。这是真实的，即使是UC H II区显示非常弱的Brγ发射。虽然Brγ通常与射电辐射在空间上相关，但H2与UC H II区域的相关性很小，通常位于距离中心射电辐射约10'处。每个UC H II研究区域的讨论包括在一个广泛的附录。
A near-infrared (NIR) survey of 63 radio-selected, ultracompact (UC) H II regions representing 47 different star-forming sites has been completed. The survey was obtained using H-band imaging and moderate-resolution, R = 1200, K-band spectroscopy, centered on the radio emission peak of the UC H II regions. The goal of this survey was to determine the fraction of radio-selected UC H II regions that can be studied with NIR observations and analysis. Approximately 50% of the 63 radio-selected UC H II regions appear to be detected at NIR wavelengths in Brγ emission (107 ergs s-1 cm-2 sr-1). Typical line-of-sight extinction toward the detected UC H II regions ranged from AV = 30 to 50, though one source was measured to have AV = 80. For a few of these UC H II regions, the central ionizing sources are detected through high signal-to-noise ratio NIR spectra of photospheric transitions. This preliminary survey suggests that perhaps 5%-10% of UC H II regions showing NIR counterparts will have directly detectable central ionizing sources. Using the ratio of He I 2.11 to Brγ, the effective temperatures of the central ionizing stars in 25 UC H II regions have been estimated. While He I is not always detected in UC H II regions, when it was found or a meaningful upper limit determined, the spectral type implied by the ratio of He I 2.11 to Brγ closely matched similar estimates of spectral type derived from radio. Model predictions based on mid-infrared measurements appear to underestimate the temperature of the central ionizing stars for which we have directly detected spectral types. The line ratios of H2 2-1 S(1) and 1-0 S(0) relative to the 1-0 S(1) line in our sample of UC H II regions are generally indicative of dense photodissociation regions rather than shocks, similar to what is seen in the Orion Bar. This was true even for UC H II regions showing very weak Brγ emission. While Brγ was generally found to be spatially correlated with the radio emission, H2 showed little correlation with the UC H II regions, typically lying ≳10' from the central radio emission. A discussion of each UC H II region studied is included in an extensive appendix.