We present results from Giant Metrewave Radio Telescope and Chandra observations of the NGC 1550 galaxy group. Although previously thought of as relaxed, we show evidence that gas sloshing and active galactic nucleus (AGN) heating have affected the structure of the system. The 610 and 235 MHz radio images show an asymmetric jet-lobe structure with a total size of similar to 33 kpc, with a sharp kink at the base of the more extended western jet, and bending of the shorter eastern jet as it enters the lobe. The 235-610 MHz spectral index map shows that both radio lobes have steep spectral indices (alpha(610)(235) >= -1.5), indicating the presence of an old electron population. The X-ray images reveal an asymmetric structure in the hot gas correlated with the radio structure, as well as potential cavities coincident with the radio lobes, with rims and arms of gas that may have been uplifted by the cavity expansion. The X-ray residual map reveals an arc-shaped structure to the east that resembles a sloshing cold front. Radio spectral analysis suggests a radiative age of about 33 Myr for the source, comparable to the sloshing time-scale and dynamical estimates of the age of the lobes. An estimate of the mechanical energy required to inflate the cavities suggests that the AGN of NGC 1550 is capable of balancing radiative losses from the intragroup medium (IGM) and preventing excessive cooling, providing that the AGN jets are efficiently coupled to the IGM gas. In conclusion, we find evidence of sloshing motions from both radio and X-ray structures, suggesting that NGC 1550 was perturbed by a minor merger or infalling galaxy about 33 Myr ago.

中文翻译：

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X射线发光NGC 1550星系群中AGN反馈和晃动的证据

我们展示了巨型米波射电望远镜和 NGC 1550 星系群的钱德拉观测结果。尽管以前被认为是放松的，但我们展示了气体晃动和活动星系核 (AGN) 加热影响了系统结构的证据。610 和 235 MHz 无线电图像显示了一个不对称的喷射叶结构，总大小类似于 33 kpc，在更延伸的西部喷射流的底部有一个尖锐的扭结，而较短的东部喷射流在进入叶瓣时弯曲. 235-610 MHz 频谱指数图显示两个射电瓣都有陡峭的频谱指数（alpha(610)(235) >= -1.5），表明存在旧电子群。X 射线图像揭示了与射电结构相关的热气体中的不对称结构，以及与射电瓣重合的潜在空腔，带有可能因空腔膨胀而被抬升的边缘和气体臂。X 射线残差图显示东面有一个弧形结构，类似于晃动的冷锋。射电频谱分析表明该源的辐射年龄约为 33 Myr，与对波瓣年龄的晃动时间尺度和动力学估计相当。对空腔充气所需机械能的估计表明，NGC 1550 的 AGN 能够平衡群内介质 (IGM) 的辐射损失并防止过度冷却，前提是 AGN 射流与 IGM 气体有效耦合。总之，我们从射电和 X 射线结构中找到了晃动运动的证据，这表明 NGC 1550 受到了大约 33 Myr 前的小合并或下落星系的扰动。