USING RADIO HALOS AND MINIHALOS TO MEASURE THE DISTRIBUTIONS OF MAGNETIC FIELDS AND COSMIC RAYS IN GALAXY CLUSTERS
USING RADIO HALOS AND MINIHALOS TO MEASURE THE DISTRIBUTIONS OF MAGNETIC FIELDS AND COSMIC RAYS IN GALAXY CLUSTERS
复制标题
利用射电晕和迷你晕测量星系团中磁场和宇宙线的分布
DOI：
10.1088/0004-637x/722/1/737
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
A. Loeb
中科院分区：
文献类型：
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作者：
U. Keshet;A. Loeb
一些星系团以Mpc尺度上的巨晕（GH）或较小尺度上的迷你晕（MH）的形式显示出弥散的射电辐射。比较甚大阵列和XMM牛顿径向配置文件的几个这样的集群，我们发现一个普遍的线性相关性之间的无线电和X射线表面亮度，有效的两种类型的晕。这意味着晕的中心发射率νjν = 10−31.4 ± 0.2（n/10−2cm−3）2（T/T0）0.2 ± 0.5ergs−1cm−3，其中T和T0分别是局部和中心温度，n是电子数密度。我们认为，紧密的相关性和标度的jν，结合形态和光谱的证据，表明GH和MH产生的二次电子和正电子，产生于宇宙射线离子（CRI）碰撞与强磁化的B 3μG的团内气体。当磁能密度下降到微波背景之下时，无线电发射大大减弱，产生具有cluronic形态的晕（例如，RXC J2003.5 − 2323和A2255）或明显的径向断裂。因此，我们在A2029和英仙座的半径分别为r = 110 kpc和r = 50 kpc处测量到磁场B = 3μG。20 GeV强碰撞产生的秒谱反映了碰撞截面的能量依赖性。我们利用观测到的晕的光谱，特别是当它们随着半径或频率的增加而变陡时，来（1）测量B 10（ν/700 MHz）μG，其中ν是谱突变频率，（2）确定平均谱与中心磁场之间的相关性，以及（3）在10 GeV以上的粒子能量下，推断出CRI谱指数s −2.7和能量分数p 10−3.6 ± 0.2。我们的研究结果有利于一个模型，CRI扩散远离他们的来源（这可能是超新星，根据初步的相关性与星星形成），而磁场产生的合并在GH和核心晃动在MH。
Some galaxy clusters show diffuse radio emission in the form of giant halos (GHs) on Mpc scales or minihalos (MHs) on smaller scales. Comparing Very Large Array and XMM-Newton radial profiles of several such clusters, we find a universal linear correlation between radio and X-ray surface brightness, valid in both types of halos. It implies a halo central emissivity νjν = 10−31.4 ± 0.2(n/10−2cm−3)2(T/T0)0.2 ± 0.5ergs−1cm−3, where T and T0 are the local and central temperatures, respectively, and n is the electron number density. We argue that the tight correlation and the scaling of jν, combined with morphological and spectral evidence, indicate that both GHs and MHs arise from secondary electrons and positrons, produced in cosmic-ray ion (CRI) collisions with a strongly magnetized B ≳ 3μG intracluster gas. When the magnetic energy density drops below that of the microwave background, the radio emission weakens considerably, producing halos with a clumpy morphology (e.g., RXC J2003.5 − 2323 and A2255) or a distinct radial break. We thus measure a magnetic field B = 3μG at a radius r ≃ 110kpc in A2029 and r ≃ 50kpc in Perseus. The spectrum of secondaries, produced from hadronic collisions of ∼20GeV CRIs, reflects the energy dependence of the collision cross section. We use the observed spectra of halos, in particular where they steepen with increasing radius or frequency, to (1) measure B ≃ 10(ν/700MHz)μG with ν the spectral break frequency, (2) identify a correlation between the average spectrum and the central magnetic field, and (3) infer a CRI spectral index s ≲ −2.7 and energy fraction ξp ∼ 10−3.6 ± 0.2 at particle energies above 10 GeV. Our results favor a model where CRIs diffuse away from their sources (which are probably supernovae, according to a preliminary correlation with star formation), whereas the magnetic fields are generated by mergers in GHs and by core sloshing in MHs.
DOI：
10.1007/978-1-4020-6941-3_8
发表时间：
2008
期刊：
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影响因子：
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作者：
Birkinshaw M
通讯作者：
Birkinshaw M