We present results on global very long baseline interferometry (VLBI) observations at 327 MHz of 18 compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources from the 3C and the Peacock & Wall catalogues. About 80 per cent of the sources have a ‘double/triple’ structure. The radio emission at 327 MHz is dominated by steep-spectrum extended structures, while compact regions become predominant at higher frequencies. As a consequence, we could unambiguously detect the core region only in three sources, likely due to self-absorption affecting its emission at this low frequency. Despite their low surface brightness, lobes store the majority of the source energy budget, whose correct estimate is a key ingredient in tackling the radio source evolution. Low-frequency VLBI observations able to disentangle the lobe emission from that of other regions are therefore the best way to infer the energetics of these objects. Dynamical ages estimated from energy budget arguments provide values between 2 × 103 and 5 × 104 yr, in agreement with the radiative ages estimated from the fit of the integrated synchrotron spectrum, further supporting the youth of these objects. A discrepancy between radiative and dynamical ages is observed in a few sources where the integrated spectrum is dominated by hotspots. In this case the radiative age likely represents the time spent by the particles in these regions, rather than the source age.

中文翻译：

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来自 3C 和 PW 样本的 327 MHz 紧凑陡峭频谱和 GHz 峰值频谱源的 VLBI 图像

我们展示了来自 3C 和 Peacock & Wall 目录的 18 个紧凑陡谱 (CSS) 和 GHz 峰值频谱 (GPS) 无线电源在 327 MHz 处的全球超长基线干涉测量 (VLBI) 观测结果。大约 80% 的来源具有“双重/三重”结构。327 MHz 的无线电发射主要由陡频谱扩展结构主导，而紧凑区域则在较高频率下占主导地位。因此，我们只能在三个来源中明确地检测到核心区域，这可能是由于自吸收影响了它在这个低频下的发射。尽管表面亮度低，但波瓣存储了大部分源能量预算，其正确估计是解决无线电源演变的关键因素。因此，能够将波瓣发射与其他区域的波瓣发射分开的低频 VLBI 观测是推断这些物体能量学的最佳方法。从能量预算参数估计的动态年龄提供了 2 × 103 和 5 × 104 年之间的值，这与根据集成同步加速器光谱的拟合估计的辐射年龄一致，进一步支持了这些物体的年轻化。在集成光谱以热点为主的几个来源中观察到辐射年龄和动力年龄之间的差异。在这种情况下，辐射年龄可能代表粒子在这些区域所花费的时间，而不是源年龄。与根据集成同步加速器光谱的拟合估计的辐射年龄一致，进一步支持了这些物体的年轻化。在集成光谱以热点为主的几个来源中观察到辐射年龄和动力年龄之间的差异。在这种情况下，辐射年龄可能代表粒子在这些区域所花费的时间，而不是源年龄。与根据集成同步加速器光谱的拟合估计的辐射年龄一致，进一步支持了这些物体的年轻化。在集成光谱以热点为主的几个来源中观察到辐射年龄和动力年龄之间的差异。在这种情况下，辐射年龄可能代表粒子在这些区域所花费的时间，而不是源年龄。