The Rotating Nuclear Star Cluster in NGC 4244

TL;DR

This study uses advanced infrared spectroscopy to reveal the rotating, multi-component structure of the nuclear star cluster in NGC 4244, providing insights into its formation mechanisms.

Contribution

First detailed kinematic analysis of NGC 4244's nuclear star cluster showing rotation and multiple stellar populations, supporting specific formation scenarios.

Findings

Detected 30 km/sec rotation within 10 pc of the cluster.

Measured a central velocity dispersion of 28 km/sec.

Identified multiple stellar populations through spectral variations.

Abstract

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/sec within the central 10 pc (0.5") of the cluster. The central velocity dispersion is found to be 28+/-2 km/sec. 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.