CBI limits on 31 GHz excess emission in southern H ii regions
CBI limits on 31 GHz excess emission in southern H ii regions
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CBI 对南部 H ii 地区 31 GHz 超量发射的限制
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
U. Chile
中科院分区：
文献类型：
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作者：
C. Dickinson;R. Davies;L. Bronfman;S. Casassus;R. Davis;T. Pearson;A. Readhead;P. Jpl;Caltech;Jbo;U. Chile
我们已经用宇宙背景成像仪绘制了31 GHz的银河系南部平面的四个区域。从这些地图中，我们提取了南方天空中最亮的六个HⅡ区的通量密度，并将它们与文献中的多频数据进行了比较。对每个源的光谱指数的拟合值接近于光学薄层自由辐射的理论值，从而证实了31 GHz处的大部分通量是由电子温度为≈7000-8000K的电离气体的自由辐射引起的。
我们还发现，对于所有六个源，31 GHz的通量密度略高于文献中数据的预测值。这种过量排放可能是由于旋转的尘埃或其他排放机制造成的。与100μm数据的比较表明，尘埃的平均发射率为3.3±1.7μK(mJy锶^(−1))^(−1)，或95%的置信限<；6.1μK(mJy锶^(−1))^(−1)。这比在银河系高纬度的扩散云中发现的要低3-4倍。最显著的探测(3.3GHz)是在G284.3RCW0.3(∼49)中发现的，可能占到在31σ观测到的总通量密度的30%。在这里，超额发射的尘埃发射率为13.6±4.2mJyμK(mJy SR^(−1))^(−1)，处于银河系高纬度观测范围内。
在所有六个源中都观察到了低水平的极化发射，偏振分数在0.3-0.6%范围内。这可能主要是由于仪器的泄漏，因此是自由-自由极化的上限。这相当于反常发射的偏振上限为~1%。
We have mapped four regions of the southern Galactic plane at 31 GHz with the Cosmic Background Imager. From the maps, we have extracted the flux densities for six of the brightest H ii regions in the southern sky and compared them with multifrequency data from the literature. The fitted spectral index for each source was found to be close to the theoretical value expected for optically thin free–free emission, thus confirming that the majority of flux at 31 GHz is due to free–free emission from ionized gas with an electron temperature of ≈7000–8000 K.
We also found that, for all six sources, the 31-GHz flux density was slightly higher than the predicted value from data in the literature. This excess emission could be due to spinning dust or another emission mechanism. Comparisons with 100-μm data indicate an average dust emissivity of 3.3 ± 1.7 μK (MJy sr^(−1))^(−1) , or a 95 per cent confidence limit of <6.1 μK (MJy sr^(−1))^(−1) . This is lower than that found in diffuse clouds at high Galactic latitudes by a factor of ∼3–4. The most significant detection (3.3σ) was found in G284.3−0.3 (RCW 49) and may account for up to ≈30 per cent of the total flux density observed at 31 GHz. Here, the dust emissivity of the excess emission is 13.6 ± 4.2 μK (MJy sr^(−1))^(−1) and is within the range observed at high Galactic latitudes.
Low-level polarized emission was observed in all six sources with polarization fractions in the range 0.3–0.6 per cent. This is likely to be mainly due to instrumental leakage and is therefore an upper limit to the free–free polarization. It corresponds to an upper limit of ~1 per cent for the polarization of anomalous emission.