INTEGRATED RADIO CONTINUUM SPECTRA OF GALAXIES
INTEGRATED RADIO CONTINUUM SPECTRA OF GALAXIES
复制标题
星系的综合射电连续谱
DOI：
10.1088/0004-6256/149/1/32
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
J. Eilek
中科院分区：
文献类型：
--
作者：
J. Marvil;F. Owen;J. Eilek
我们研究了大量明亮星系样本的 74 MHz 至 5 GHz（波长 400-6 cm）总连续辐射的光谱形状。我们利用 VLA 低频巡天、Westerbork 北方巡天、NRAO VLA 巡天和 Green Bank 6 厘米巡天的重叠巡天覆盖范围，与之前的此类工作相比，获得了更好的分辨率、灵敏度和样本量。对于我们的 250 个明亮星系样本，我们测量了平均光谱指数 α，在 1.4 和 4.85 GHz 之间为 -0.69，在 325 MHz 和 1.4 GHz 之间为 -0.55，在 74 和 325 MHz 之间为 -0.45，这相当于平均光谱中曲率的检测。当与具有恒定曲率的广义函数拟合时，该曲率的大小大约为每个对数频率十年 Δα = -0.2。我们的数据中没有明显的低频光谱平坦化与星系倾角的趋势，这表明自由-自由吸收并不是对观测到的曲率的令人满意的解释。热发射与非热发射的比率通过两种独立的方法估算：(1) 使用 IRAS 远红外通量；(2) 使用总光谱指数值。方法(1)导致1.4GHz热分数的分布为9%±3%，这与之前的研究一致，而方法(2)产生平均1.4GHz热分数为51%，色散为26%。方法 (2) 产生的高度难以置信的值表明，典型幂律热分量和非热分量之和对于 325 和 1.4GHz 之间的总光谱指数来说不是一个可行的模型。对光谱指数、红外衍生量和其他源特性之间关系的研究表明，我们的样本中射电光度高的星系平均而言具有更平坦的射电光谱指数，并且与后来类型的射电-红外比率相比，早期类型往往具有过量的射电发射。与星系的光学尺寸相比，早期类型的射电发射也比后期类型的星系更紧凑。尽管存在这些差异，但没有检测到光谱指数和星系类型之间的关系。
We investigate the spectral shape of the total continuum radiation, between 74 MHz and 5 GHz (400–6 cm in wavelength), for a large sample of bright galaxies. We take advantage of the overlapping survey coverage of the VLA Low-Frequency Sky Survey, the Westerbork Northern Sky Survey, the NRAO VLA Sky Survey, and the Green Bank 6 cm Survey to achieve significantly better resolution, sensitivity, and sample size compared to prior efforts of this nature. For our sample of 250 bright galaxies we measure a mean spectral index, α, of −0.69 between 1.4 and 4.85 GHz, −0.55 between 325 MHz and 1.4 GHz, and −0.45 between 74 and 325 MHz, which amounts to a detection of curvature in the mean spectrum. The magnitude of this curvature is approximately Δα = −0.2 per logarithmic frequency decade when fit with a generalized function having constant curvature. No trend in low-frequency spectral flattening versus galaxy inclination is evident in our data, suggesting that free–free absorption is not a satisfying explanation for the observed curvature. The ratio of thermal to non-thermal emission is estimated through two independent methods: (1) using the IRAS far-IR fluxes and (2) with the value of the total spectral index. Method (1) results in a distribution of 1.4 GHz thermal fractions of 9% ± 3%, which is consistent with previous studies, while method (2) produces a mean 1.4 GHz thermal fraction of 51% with dispersion 26%. The highly implausible values produced by method (2) indicate that the sum of typical power-law thermal and non-thermal components is not a viable model for the total spectral index between 325 and 1.4 GHz. An investigation into relationships between spectral index, infrared-derived quantities, and additional source properties reveals that galaxies with high radio luminosity in our sample are found to have, on average, a flatter radio spectral index, and early types tend to have excess radio emission when compared to the radio–infrared ratio of later types. Early types also have radio emission that is more compact than later type galaxies, as compared to the optical size of the galaxy. Despite these differences, no relation between spectral index and galaxy type is detected.
M 31 和 M 33 的多尺度射电红外关联：磁场和恒星形成的作用
影响因子：
6.5
作者：
Tabatabaei
通讯作者：
Tabatabaei