发表机构
Steward Observatory, University of Arizona; Department of Physics and Astronomy, Dartmouth College; Department of Physics and Astronomy, Tufts University; Department of Physics and Astronomy, University of Tampa; Space Telescope Science Institute; Department of Physics, University of Surrey; Department of Physics, Engineering Physics and Astronomy, Queen’s University（亚利桑那大学斯图尔德天文台; 达特茅斯学院物理与天文学系; 塔夫茨大学物理与天文学系; 坦帕大学物理与天文学系; 太空望远镜科学研究所; 萨里大学物理系; 女王大学物理、工程物理与天文学系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
利用JWST档案数据在M82晕中发现四个弥散星团，通过等时线拟合和光度测量确认其年老贫金属性质，大小5.4-10.5 pc，光度M_V约-4.1至-6.4，填补了星团与矮星系之间的空白区域。
AI 中文摘要
弥散星团（DSCs）在大小-光度平面上占据了一个研究较少的区域，介于经典球状星团（GCs）和矮星系之间。在此，我们利用档案JWST/NIRCam成像报告了在附近星暴星系M82的晕中发现了四个微弱的弥散星团。我们在所有四个系统中分辨出了单独的恒星，其颜色-星等图与主要包含年老（约10 Gyr）恒星族的等时线比较结果一致。DSC 1拥有一个贫金属星族（[M/H]~-2），而DSC 2、3和4则更适合用[M/H]~-0.8的等时线来表示。为了确定它们的性质，我们使用增长曲线和径向轮廓拟合测量了它们的大小和综合星等，这两种方法得到的结果一致。DSC的大小范围约为5.4至10.5秒差距，比典型的球状星团（2-3秒差距）更延展。它们的光度范围在M_V约-4.1至-6.4之间，比之前已知的M82星团（SC）星族暗约1个星等。在这些低光度下，这些系统占据了大小-光度平面中一个稀疏采样的区域，在该区域中星团和矮星系之间的区别变得越来越模糊。最值得注意的是，DSC 3是迄今为止在M82中识别出的最暗的星团候选体，接近了银河系超微弱致密卫星所占据的区域。这些微弱的弥散星团仅通过目视检查就被识别出来，这表明它们可能在现有的星团目录中代表性不足，并且基于JWST的邻近星系档案搜索将会富有成效。
英文摘要
Diffuse star clusters (DSCs) occupy a poorly explored region of the size-luminosity plane between classical globular clusters (GCs) and dwarf galaxies. Here we report the discovery of four faint DSCs in the halo of the nearby starburst galaxy M82 using archival JWST/NIRCam imaging. We resolve individual stars in all four systems, whose color-magnitude diagrams are consistent with predominantly old ($\sim10$ Gyr) stellar populations, based on comparison with isochrones. DSC 1 hosts a metal-poor population ($[\mathrm{M/H}]\sim-2$), while DSCs 2, 3 and 4 are better represented by $[\mathrm{M/H}]\sim-0.8$ isochrones. To establish their nature, we measure their sizes and integrated magnitudes using curve-of-growth and radial profile fits, which yield consistent results between these methods. The sizes of DSCs range from $\sim$ 5.4 to 10.5 pc, making them more extended than typical GCs (2-3 pc). Their luminosities span M$_{\rm V}\simeq-4.1$ to $-6.4$, reaching $\sim$ 1 mag fainter than the previously known M82 star cluster (SC) population. At these low luminosities, the systems occupy a sparsely sampled region of the size-luminosity plane where the distinction between SCs and dwarf galaxies becomes increasingly ambiguous. Most notably, DSC 3 is the faintest SC candidate identified in M82 to date and approaches the regime occupied by Milky Way ultra-faint compact satellites. These faint DSCs were identified through visual inspection alone, suggesting they are likely underrepresented in existing star cluster catalogs, and that a JWST-based archival search of nearby galaxies would be fruitful.
Comments16 pages, 7 figures, 3 tables. Submitted to ApJL, comments welcome!
