“普通”早型星系的整体性质：NGC 4494中恒星和球状星团的光度学和光谱学
Global Properties of `Ordinary' Early-type Galaxies: photometry and spectroscopy of stars and globular clusters in NGC 4494
摘要：
我们提出了一个全面的分析的空间，运动学和化学性质的恒星和球状星团（GC）的“普通”椭圆星系NGC 4494使用的数据从凯克和斯巴鲁望远镜。我们推导出星系表面亮度和颜色的配置文件，以大银河中心半径。我们将后者与使用近红外钙三重态获得的金属丰度进行比较。我们得到恒星的运动到~3.5有效半径。与相对较圆的光度等照度线相比，后者在超过约1.8有效半径时显得扁平或拉长。事实上，NGC 4494可能是一个扁平的星系，甚至可能是一个S 0，在45度的倾角看到。我们公布了431个GC候选人的目录，亮度比i=24的测光的基础上，其中109个光谱确认和54个光谱金属丰度测量。我们还报告了在NGC 4494周围发现了3个光谱证实的超致密矮星，测量的金属丰度为-0.4<[Fe/H]<-0.3。根据它们的性质，我们得出结论，它们只是明亮的GC。贫金属的球状星团的自转幅度与星系相似，而富金属的球状星团则表现为边缘自转。我们用现有的文献数据和结果补充我们的分析。利用星系形成的模型预测和一套合并模拟，我们发现NGC 4494的许多观测性质可以用相对较新的富含气体的主要合并来解释。对单个星系的完整研究结合了一系列的观测途径和方法，如这里所介绍的，将是一个宝贵的工具，用于限制星系形成模型的细节，特别是在大的银河系中心半径。
英文摘要：
We present a comprehensive analysis of the spatial, kinematic, and chemical properties of stars and globular clusters (GCs) in the `ordinary' elliptical galaxy NGC 4494 using data from the Keck and Subaru telescopes. We derive galaxy surface brightness and colour profiles out to large galactocentric radii. We compare the latter to metallicities derived using the near-infrared Calcium Triplet. We obtain stellar kinematics out to ~3.5 effective radii. The latter appear flattened or elongated beyond ~1.8 effective radii in contrast to the relatively round photometric isophotes. In fact, NGC 4494 may be a flattened galaxy, possibly even an S0, seen at an inclination of ~45 degrees. We publish a catalogue of 431 GC candidates brighter than i=24 based on the photometry, of which 109 are confirmed spectroscopically and 54 have measured spectroscopic metallicities. We also report the discovery of 3 spectroscopically confirmed ultra-compact dwarfs around NGC 4494 with measured metallicities of -0.4<[Fe/H]<-0.3. Based on their properties, we conclude that they are simply bright GCs. The metal-poor globular clusters are found to be rotating with similar amplitude as the galaxy stars, while the metal-rich globular clusters show marginal rotation. We supplement our analysis with available literature data and results. Using model predictions of galaxy formation, and a suite of merger simulations, we find that many of the observational properties of NGC 4494 may be explained by formation in a relatively recent gas-rich major merger. Complete studies of individual galaxies incorporating a range of observational avenues and methods such as the one presented here will be an invaluable tool for constraining the fine details of galaxy formation models, especially at large galactocentric radii.
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