标题： NGC 3628-UCD1：嵌入在恒星流中的可能的$ω$ Cen 类似物 显示英文标题

标题： NGC 3628-UCD1: A possible $ω$ Cen Analog Embedded in a Stellar Stream

摘要： 使用 Subaru/Suprime-Cam 广域成像以及 Keck/ESI 和 LBT/MODS 光谱学，我们识别并表征了一个嵌在螺旋星系 NGC 3628 周围恒星流中的紧凑星团，我们将其称为 NGC 3628-UCD1。UCD1 的大小和亮度与$\omega$ Cen 相似，后者是银河系中最明亮的球状星团，长期以来一直被认为是一个被吸积矮星系的剥离残余。该天体的视星等为$i=19.3$ mag (${\rm L}_{\rm i}=1.4\times10^{6}~{\rm L}_{\odot}$)。UCD1 在我们的地面成像中勉强被分辨，其半光半径为$\sim10$ pc。我们测量了恒星流的综合亮度为$i=13.1$ mag，其中$(g-i)=1.0$。这将对应于一个大约亮度为${\rm L}_i\sim4.1\times10^{8}~{\rm L}_{\odot}$的被吸积矮星系。 Spectral analysis reveals that UCD1 has an age of $6.6$ Gyr , $[\rm{Z}/\rm{H}]=-0.75$, an $[{\alpha}/\rm{Fe}]=-0.10$. We propose that UCD1 is an example of an $\omega$ Cen-like star cluster possibly forming from the nucleus of an infalling dwarf galaxy, demonstrating that at least some of the massive star cluster population may be created through tidal stripping. 显示英文摘要

摘要： Using Subaru/Suprime-Cam wide-field imaging and both Keck/ESI and LBT/MODS spectroscopy, we identify and characterize a compact star cluster, which we term NGC 3628-UCD1, embedded in a stellar stream around the spiral galaxy NGC 3628. The size and luminosity of UCD1 are similar to $\omega$ Cen, the most luminous Milky Way globular cluster, which has long been suspected to be the stripped remnant of an accreted dwarf galaxy. The object has a magnitude of $i=19.3$ mag (${\rm L}_{\rm i}=1.4\times10^{6}~{\rm L}_{\odot}$). UCD1 is marginally resolved in our ground-based imaging, with a half-light radius of $\sim10$ pc. We measure an integrated brightness for the stellar stream of $i=13.1$ mag, with $(g-i)=1.0$. This would correspond to an accreted dwarf galaxy with an approximate luminosity of ${\rm L}_i\sim4.1\times10^{8}~{\rm L}_{\odot}$. Spectral analysis reveals that UCD1 has an age of $6.6$ Gyr , $[\rm{Z}/\rm{H}]=-0.75$, an $[{\alpha}/\rm{Fe}]=-0.10$. We propose that UCD1 is an example of an $\omega$ Cen-like star cluster possibly forming from the nucleus of an infalling dwarf galaxy, demonstrating that at least some of the massive star cluster population may be created through tidal stripping.