Asymmetries in the jets of weak radio galaxies
Asymmetries in the jets of weak radio galaxies
复制标题
弱射电星系喷流的不对称性
DOI：
--
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
R. Fanti
中科院分区：
文献类型：
--
作者：
R. Laing;P. Parma;H. D. Ruiter;R. Fanti
我们描述了从B2样本中选出的FR I射电星系喷流中kpc尺度的边到边不对称性的研究。基本数据是射流表面亮度和宽度，通过将横向剖面拟合到距核心一定距离范围内的甚大阵列（VLA）图像来确定。在一个给定的距离，从核之间的差异被解释为多普勒光束的影响，本质上是对称的流动，并与Laing和Bridle为3C 31推导的模型和更简单的变体进行了比较。喷流/反喷流亮度比的主喷流第一次增亮与核心日珥，预期的相对论流。根据亮度比的分布，我们推断喷流在它们第一次爆发和变亮的地方有一个最大速度为0.9c，但也有证据表明还有其他较慢的物质。减速到次相对论速度的尺度随无线电功率的增加而增加。大多数在1.4 GHz下光度<1024 WHz-1的源中的喷流在核心的2 kpc内变得基本对称（因此是次相对论性的）。在更强大的源中，在前2 kpc内闪耀的喷流在10 kpc时变得对称，但是最明亮的物体的子集具有在更大距离内保持不对称的喷流。较亮的喷流耀斑出现的点对应于静止坐标系发射率的突然增加，但到主喷流和反喷流耀斑点的距离比与亮度比呈负相关，正如减速相对论流所预期的那样。亮度和半高宽（FWHM）的比率也是相关的，我们解释为多普勒波束的流动，其中速度从射流轴径向向外减小的结果的效果。喷流减速的夹带外部物质提供了一个自然的解释，这些速度梯度。喷流的能量通量是大致一致的能量供应的瓣源寿命估计光谱指数测量。我们的结果是定性一致的FR I射电星系和BL Lac对象的统一模型，但需要一些修改的标准图片。
We describe a study of the side-to-side asymmetries on kpc scales in the jets of FR I radio galaxies selected from the B2 sample. The basic data are jet surface brightnesses and widths determined by fitting transverse profiles to Very Large Array (VLA) images at a range of distances from the core. Differences between the jets at a given distance from the nucleus are interpreted as effects of Doppler beaming on intrinsically symmetrical flows and are compared with the model derived for 3C31 by Laing & Bridle and with simpler variants. The jet/counterjet brightness ratios where the main jet first brightens are correlated with core prominence, as expected for a relativistic flow. From the distribution of brightness ratios, we infer that jets have a maximum velocity ≈0.9c where they first flare and brighten, but there is also evidence for additional slower material. Deceleration to subrelativistic speeds occurs on scales which increase with radio power. Jets in the majority of sources with luminosities <1024 WHz-1 at 1.4 GHz become essentially symmetrical (and therefore subrelativistic) within 2 kpc of the core. In more powerful sources, jets that flare within the first 2 kpc become symmetrical by 10 kpc, but a subset of the most luminous objects has jets which remain asymmetrical to larger distances. The point at which the brighter jet flares appears to correspond to a sudden increase in rest-frame emissivity, but the ratio of distances to the flaring point in main and counterjets is anticorrelated with brightness ratio, as expected for a decelerating relativistic flow. Brightness and full width at half-maximum (FWHM) ratios are also anticorrelated, an effect which we interpret as a result of Doppler beaming for a flow in which the velocity decreases radially outwards from the jet axis. Jet deceleration by entrainment of external material provides a natural explanation for these velocity gradients. The jet energy flux is roughly consistent with energy supply to the lobes over a source lifetime estimated from spectral index measurements. Our results are qualitatively consistent with unified models of FR I radio galaxies and BL Lac objects, but require some modifications to the standard picture.