M 87 at metre wavelengths: the LOFAR picture
M 87 at metre wavelengths: the LOFAR picture
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DOI：
10.1051/0004-6361/201220209
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发表时间：
2012-11-01
影响因子：
6.5
通讯作者：
Zarka, P.
中科院分区：
文献类型：
--
作者：
de Gasperin, F.;Orru, E.;Zarka, P.
上下文M87是一个巨大的椭圆星系，位于室女座星系团的中心，其中有一个质量为6.4x10（9）M圆点的超大质量黑洞，其活动是围绕星系的扩展（80 kpc）射电叶的原因。落在中心黑洞上的物质所产生的能量被喷射出来，并通过相对论射流和形态复杂的浮力气泡系统转移到星系团内介质中，这些气泡上升到扩展晕的边缘。为了限制活动核过去的活动周期，M87的图像是在以前从未探索过的低无线电频率下以这些高空间分辨率和动态范围产生的。为了解开不同的同步加速器模型和地方的约束源磁场，年龄和能量，我们还进行了详细的光谱分析M 87扩展射电晕。我们提出的第一个意见与新的低频阵列（LOFAR）的M 87在频率下降到20 MHz。在15-30 MHz、30-77 MHz和116-162 MHz进行了三次观测。我们使用这些观测与档案数据一起产生一个低频率的频谱指数图，并在宽的频率范围30 MHz-10 GHz的频谱分析。我们没有发现任何新的扩展排放的迹象，相反，源似乎很好地限制了集群内介质的高压。相对论性电子的连续注入是最适合我们数据的模型，并提供了一个场景，其中叶仍然由来自活动星系核的新鲜相对论性粒子提供。我们认为，在核心和晕的低频无线电光谱斜率之间的差异意味着一个强大的绝热膨胀的等离子体，只要它离开核心区域。扩展的晕圈具有近似或等于10 μ G的均分磁场强度，在粒子流更活跃的区域中，该均分磁场强度增加到近似或等于13 μ G。同步加速器老化的连续注入模型提供了一个类似或等于4000万年的晕的年龄，这反过来又提供了6-10 × 10（44）erg s（-1）的喷流动力学功率。
Context. M87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4x10(9) M-circle dot, whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo.Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo.Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15-30 MHz, 30-77 MHz and 116-162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz-10 GHz.Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intra-cluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radio-spectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of similar or equal to 10 mu G, which increases to similar or equal to 13 mu G in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of similar or equal to 40 Myr, which in turn provides a jet kinetic power of 6-10 x 10(44) erg s(-1).