We present observations of the nuclear star cluster in the nearby edge-on spiral galaxy NGC 4244 using the Gemini Near-Infrared Integral Field Spectrograph (NIFS) with laser guide star adaptive optics. From a previous study of edge-on galaxies, this nuclear star cluster was found to be one of a sample of clusters that appear flattened along the plane of their host galaxies disks. Such clusters show evidence for multiple morphological components, with younger/ bluer disk components and older/redder spheroidal components. Our new observations of NGC 4244 show clear rotation of 30 km s~(-1) within the central 10 pc (0.5") of the cluster. The central velocity dispersion is found to be 28 ± 2 km s~(-1). The multiple stellar populations inferred from the optical colors and spectra are seen as variations in the CO line strength in the NIFS spectra. The rotation is clearly detected even in the older, more spheroidal stellar component. We discuss evidence for similar structures and kinematics in the nuclear star clusters of other galaxies including M33 and the Milky Way. Our observations support two possible formation mechanisms: (1) episodic accretion of gas from the disk directly onto the nuclear star cluster; or (2) episodic accretion of young star clusters formed in the central part of the galaxy due to dynamical friction.
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机译：我们使用双子座近红外积分场光谱仪（NIFS）和激光导星自适应光学器件，对附近边缘螺旋星系NGC 4244中的核星团进行观测。根据先前对边缘星系的研究，发现该核星团是沿其主星系盘平面展平的星团样本之一。这样的簇显示出多种形态成分的证据，其中盘状成分较年轻/较蓝，而球状成分较旧/较红。我们对NGC 4244的新观测表明，在星团中心10 pc（0.5“）内，有30 km s〜（-1）明显旋转。中心速度色散为28±2 km s〜（-1）。从光学颜色和光谱推断出的多个恒星种群被视为NIFS光谱中CO谱线强度的变化，甚至在较旧的球状恒星成分中也清楚地检测到了旋转，我们讨论了类似结构和运动学的证据。包括M33和银河系在内的其他星系的核星团，我们的观察结果支持两种可能的形成机制：（1）气体从圆盘上直接向核星团上的积聚;或（2）形成于该星系中的年轻星团的积聚。由于动力摩擦，银河系的中心部分。
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