GMRT 333‐MHz observations of six nearby normal galaxies
GMRT 333‐MHz observations of six nearby normal galaxies
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对六个附近正常星系的 GMRT 333 MHz 观测
DOI：
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发表时间：
2011
期刊：
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通讯作者：
C. Ishwara
中科院分区：
文献类型：
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作者：
A. Basu;D. Mitra;Y. Wadadekar;C. Ishwara
我们报告了巨型米波射电望远镜 (GMRT) 在 333 MHz 频率下对六个附近正常星系的连续观测。观测星系的角分辨率优于 ~20 角秒（对应于约 0.4–1 kpc 的线性尺度）。这些观测结果对所有感兴趣的角尺度都很敏感，因为 GMRT 中最短基线的分辨率大于星系的角大小。此外，对于其中五个星系，我们表明在 333 MHz 时，平均热分数小于 5%。使用大约 1 GHz 的档案数据，我们估计该频率下的平均热分数约为 10%。我们还发现，在热分数较低的区域和/或位于星系外部的区域，非热光谱指数通常更陡。在高热分数区域，非热谱指数更平坦，分布窄，峰值为~−0.78，分布范围为0.16，这对~1 kpc尺度的宇宙射线电子的产生、扩散和能量损失的物理条件提出了严格的限制。
We report Giant Metrewave Radio Telescope (GMRT) continuum observations of six nearby normal galaxies at 333 MHz. The galaxies are observed with angular resolutions better than ∼20 arcsec (corresponding to a linear scale of about 0.4–1 kpc). These observations are sensitive to all angular scales of interest, since the resolution of the shortest baseline in GMRT is greater than the angular size of the galaxies. Furthermore, for five of these galaxies we show that at 333 MHz, the mean thermal fraction is less than 5 per cent. Using archival data at about 1 GHz, we estimate the mean thermal fraction to be about 10 per cent at that frequency. We also find that the non-thermal spectral index is generally steeper in regions with low thermal fraction and/or located in the outer parts of the galaxy. In regions of high thermal fraction, the non-thermal spectral index is flatter, and has a narrow distribution peaking at ∼−0.78 with a spread of 0.16, putting stringent constraints on the physical conditions for generation, diffusion and energy losses of cosmic ray electrons at scales of ∼1 kpc.