我们是否在观测NGC 4654星系中正在形成的NSC？
Are we observing a NSC in course of formation in the NGC 4654 galaxy?
摘要：
我们使用直接的$N$ -体模拟来探索一些可能的方案，为两个大质量的星系团的未来演化观测到的中心的NGC 4654，一个螺旋星系的质量类似于银河系。使用档案HST数据，我们得到的光度质量的两个集群，$M=3\times 10^5$ M $_\odot$和$M=1.7\times 10^6$ M $_\odot$，他们的半光半径，$R_{\rm eff}\sim4$ pc和$R_{\rm eff} \sim 6$ pc，和他们的投影距离光度中心的星系（都$<22$ pc）。这两个星系团（$\sim 24$ pc）的结构和分离的知识提供了一个独特的观点，研究银河系中心区的大质量集群的动力学。改变一些未知的集群轨道参数，我们进行了几个$N$体模拟表明，这些集群的未来演变将不可避免地导致他们的合并。我们发现，主要取决于它们相对轨道的形状，它们将在不到8200万年的时间内合并到银河系中心。除了潮汐相互作用，适当考虑动力摩擦制动将缩短合并时间到几个百万年。我们还研究了通过这一过程在星系中心形成大质量NSC的可能性。我们的分析表明，低偏心率的轨道，相对较长的合并时间，最终合并的集群是球形的形状，与几个秒差距的有效半径和质量的有效半径范围内的顺序$10^5\,\mathrm{M_{\odot}}$。由于这样一个星系团的中心密度高于宿主星系，因此这个合并的残余物很可能是未来NSC的胚胎。
英文摘要：
We use direct $N$-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed toward the center of NGC\,4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, $M=3\times 10^5$ M$_\odot$ and $M=1.7\times 10^6$ M$_\odot$, their half-light radii, $R_{\rm eff}\sim4$ pc and $R_{\rm eff} \sim 6$ pc, and their projected distances from the photometric center of the galaxy (both $<22$ pc). The knowledge of the structure and separation of these two clusters ($\sim 24$ pc) provides a unique view for studying the dynamics of a galactic central zone hosting massive clusters. Varying some of the unknown clusters orbital parameters, we carry out several $N$-body simulations showing that the future evolution of these clusters will inevitably result in their merger. We find that, mainly depending on the shape of their relative orbit, they will merge into the galactic center in less than 82 Myr. In addition to the tidal interaction, a proper consideration of the dynamical friction braking would shorten the merging times up to few Myr. We also investigate the possibility to form a massive NSC in the center of the galaxy by this process. Our analysis suggests that for low eccentricity orbits, and relatively long merger times, the final merged cluster is spherical in shape, with an effective radius of few parsecs and a mass within the effective radius of the order of $10^5\,\mathrm{M_{\odot}}$. Because the central density of such a cluster is higher than that of the host galaxy, it is likely that this merger remnant could be the likely embryo of a future NSC.
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