SPATIAL VARIATIONS IN THE SPECTRAL INDEX OF POLARIZED SYNCHROTRON EMISSION IN THE 9 yr WMAP SKY MAPS
SPATIAL VARIATIONS IN THE SPECTRAL INDEX OF POLARIZED SYNCHROTRON EMISSION IN THE 9 yr WMAP SKY MAPS
复制标题
9年WMAP星空图中偏振同步加速器发射光谱指数的空间变化
DOI：
10.1088/0004-637x/790/2/104
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
S. Naess
中科院分区：
文献类型：
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作者：
U. Fuskeland;I. Wehus;I. Wehus;H. Eriksen;S. Naess;S. Naess
我们使用线性回归（“T-T 图”）和最大似然两种方法来估计在 9 年威尔金森微波各向异性探测器天空图中观察到的偏振同步加速器发射的光谱指数 β。我们将天空划分为 24 个不相交的天空区域，并以 5° 为步长评估 0° 到 85° 之间所有偏振角的光谱指数。对偏振角进行平均，我们得出 23–33 GHz 频率范围内的平均光谱指数 βall-sky = −2.99 ± 0.01。我们发现，同步加速器光谱指数从银河系低纬度到高纬度陡峭了 0.14，与之前的研究一致，βplane = -2.98 ± 0.01 和 βhigh-lat = -3.12 ± 0.04 的平均光谱指数。此外，我们发现沿银河平面存在显着的纵向变化，朝向银河系中心和反中心的光谱指数比朝向银河系旋臂的光谱指数更陡。这可以通过偏移正弦曲线 β(l) = −2.85 + 0.17sin (2l − 90°) 来很好地建模。最后，我们研究了 BICEP2 场中的同步加速器发射，试图了解所声称的大规模 B 模式偏振的检测是否可以用同步加速器污染来解释。采用典型的高银河纬度光谱指数 β = −3.12，我们发现最可能的偏差对应于报告信号的约 2% (r = 0.003)。该区域数据允许的最平坦指数为 β = −2.5，在直线幂律频谱的假设下，我们发现同步加速器发射最多可占所报告的 BICEP2 信号的 20%。
We estimate the spectral index, β, of polarized synchrotron emission as observed in the 9 yr Wilkinson Microwave Anisotropy Probe sky maps using two methods, linear regression (“T–T plot”) and maximum likelihood. We partition the sky into 24 disjoint sky regions and evaluate the spectral index for all polarization angles between 0° and 85° in steps of 5°. Averaging over polarization angles, we derive a mean spectral index of βall-sky = −2.99 ± 0.01 in the frequency range of 23–33 GHz. We find that the synchrotron spectral index steepens by 0.14 from low to high Galactic latitudes, in agreement with previous studies, with mean spectral indices of βplane = −2.98 ± 0.01 and βhigh-lat = −3.12 ± 0.04. In addition, we find a significant longitudinal variation along the Galactic plane with a steeper spectral index toward the Galactic center and anticenter than toward the Galactic spiral arms. This can be well modeled by an offset sinusoidal, β(l) = −2.85 + 0.17sin (2l − 90°). Finally, we study synchrotron emission in the BICEP2 field, in an attempt to understand whether the claimed detection of large-scale B-mode polarization could be explained in terms of synchrotron contamination. Adopting a spectral index of β = −3.12, typical for high Galactic latitudes, we find that the most likely bias corresponds to about 2% of the reported signal (r = 0.003). The flattest index allowed by the data in this region is β = −2.5, and under the assumption of a straight power-law frequency spectrum, we find that synchrotron emission can account for at most 20% of the reported BICEP2 signal.