High sensitivity observations of radio halos in galaxy clusters at frequencies lower than 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos imaged down to 150-240 MHz show a considerable spread in size, morphology and spectral properties. All clusters belonging to the GMRT Radio Halo Survey with detected or candidate cluster-scale diffuse emission have been imaged at 325 MHz with the GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz. For A1682, imaging is particularly challenging due to the presence of strong and extended radio galaxies at the center. Our data analysis suggests that the radio galaxies are superposed to very low surface brightness radio emission extended on the cluster scale, which we present here.
Deep radio observations of the radio halo of the bullet cluster 1E 0657-55.8
我们提出了深1.1-3.1 GHz的澳大利亚望远镜紧凑型阵列观测的子弹状星系团，1 E 0657-55.8的射电晕。与现有的射电晕图像相比，我们的图像中的检测具有更高的意义。射电晕在星系团合并方向上的扩展与X射线辐射一样，但在垂直方向上的扩展明显小于X射线辐射。在低显着性，我们检测到一个微弱的第二个峰值在无线电晕靠近X射线质心的较小的子集群（子弹），这表明，类似于X射线发射，无线电晕可能由两个组件。最后，我们发现，独特的形状的西部边缘的无线电晕的痕迹了X射线探测到的弓激波。射电晕的形态以及射电、X射线和弱透镜性质之间缺乏强的点对点相关性表明射电晕仍在形成中。X射线冲击与一个独特的射电亮度边缘的共定位说明了冲击正在影响射电晕的结构。这些观测结果支持了激波和湍流影响射电晕同步辐射形成和演化的理论。
In this paper, we analysed the halos and voids properties of a GR-based N-body simulation carried out at redshifts z= 0.0 and z= 0.8 as differences between dynamical dark energy models (namely PL and CPL) with respect to LCDM. Analysing the halos demonstrates that both models, PL and CPL, behave like LCDM, despite the velocity dispersion of halos was more sensitive to the dynamical dark energy model. In addition, a void finder was developed to extract the properties of voids from simulated data. Further statistical model on voids confirms that the PL model produces larger voids. In summary, ou…
Here we present Halo-FDCA, a robust open source Python package for modeling and estimating total flux densities of radio (mini) halos in galaxy clusters. Radio halos are extended ( ~200 - 1500 kpc in size) synchrotron emitting sources found in galaxy clusters that trace the presence of cosmic rays and magnetic fields in the intracluster medium (ICM). These sources are centrally located and have a low surface brightness. Their exact origin is still unknown but they are likely related to cosmic rays being re-accelerated in-situ by merger or sloshing driven ICM turbulence. The presented algorithm…
We report on the detection of a giant radio halo in the cluster Abell 3404 as well as confirmation of the radio halo observed in Abell 141 (with linear extents $\sim 770$ kpc and $\sim 850$ kpc, respectively). We use the Murchison Widefield Array (MWA) in conjunction with the Australian Square Kilometre Array Pathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA) to characterise the emission and intervening radio sources from $\sim100$-$1000$ MHz; power law models are fit to the spectral energy distributions with spectral indices $α_{88}^{1110} = -1.66 \pm 0.07$ and $α_{88}^{944} …
Many galaxy clusters host Mpc scale diffuse radio sources called radio halos. Their origin is connected to the processes that lead to the formation of clusters themselves. In order to unveil this connection, statistical studies of radio halos are necessary. We selected a sample of galaxy clusters with M500>6e14Msun and z=0.08-0.33 from the Planck SZ catalogue. In paper I, we presented the radio and X-ray data analysis that we carried out on these clusters. Here, we study the radio properties of the sample, in connection to the mass and dynamical state of clusters. We used the dynamical informa…
Radio Halos From Simulations And Hadronic Models II: The Scaling Relations of Radio Halos
我们使用的结果从一个约束，宇宙学MHD模拟的本地宇宙预测无线电晕和它们的演化体积有限的一组星系团，并比较目前的观测。星团内部的模拟磁场是它们内部湍流放大的结果，磁性种子来自恒星爆发驱动的星系外流。我们评估三种模型，在那里我们选择不同的标准化的宇宙射线质子人口集群内。与我们之前对后发座星系团的分析（Donnert et al. 2010）类似，即使宇宙射线质子群中的能量分数径向增加，观测到的射电晕的径向轮廓和形态特征也无法重现。X射线光度和射电功率之间的标度关系可以被所有模型再现，但是所有模型都不能预测没有射电发射的星系团。此外，在所有模型中，我们最大的星系团的演化轨迹都未能再现观测到的射电光度双峰。这提供了额外的证据，强子，次级模型的框架是不赞成再现大规模的弥漫性无线电发射的星系团。我们还提供了预测的不可避免的发射$γ$ -射线的强子模型的完整的集群集。这些次级模型中没有一个被观测到的$γ$射线发射的极限所排除，强调大尺度漫射射电发射是限制星系团中宇宙射线质子数量的有力工具。
We investigate the use of the halo mass-gap statistic --- defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo --- as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ~25, 000 group/cluster sized halos in the mass range 10^12.5 < M_halo/M_sol < 10^14.5. In agreement with previous work, we find that halo mass-gap is related to halo formation time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration r…
We present the first detailed analysis of the radio halo in the merging galaxy cluster Abell 2256 using the LOFAR, uGMRT, and VLA. These observations combined with archival X-ray data allowed us to study the halo emission with unprecedented detail. The integrated radio emission from the entire halo is characterized by an ultra-steep spectrum, which can be described by a power law with $α_{144 \rm MHz}^{1.5 \rm GHz}=-1.63\pm0.03$, and a radial steepening in the outer regions. The halo is significantly underluminous according to the scaling relations between radio power and mass at 1.4 GHz but n…
Radio halos are synchrotron diffuse sources at the centre of a fraction of galaxy clusters. The study of large samples of clusters with adequate radio and X-ray data is necessary to investigate the origin of radio halos and their connection with the cluster dynamics and formation history. The aim of this paper is to compile a well-selected sample of galaxy clusters with deep radio observations to perform an unbiased statistical study of the properties of radio halos. We selected 75 clusters with M > = 6e14 Msun at z=0.08-0.33 from the Planck Sunyaev-Zel'dovich catalogue. Clusters without suita…
Radio halos and relics are Mpc-scale diffuse radio sources in galaxy clusters, with a steep spectral index $α>1$ ($S\propto ν^{-α}$). It has been proposed that they arise from particle acceleration induced by turbulence and weak shocks, injected in the intracluster medium (ICM) during mergers. MACS J1149.5+2223 (MACS J1149) is a high redshift ($z=0.544$) galaxy cluster possibly hosting a radio halo and a relic. We analysed LOFAR, GMRT, and JVLA radio data at 144, 323, 1500 MHz, and Chandra X-ray data to characterise the thermal and non-thermal properties of the cluster. We obtained radio image…
The central regions of galaxy clusters are permeated by magnetic fields and filled with relativistic electrons. When clusters merge, the magnetic fields are amplified and relativistic electrons are re-accelerated by turbulence in the intra cluster medium. These electrons reach energies of 1 -- 10 GeV and, in the presence of magnetic fields, produce diffuse radio halos that typically cover an area of ~1 square Mpc. Here we report observations of four clusters whose radio halos are embedded in much more extended, diffuse radio emission, filling a volume 30 times larger than that of radio halos. …
