Structure and Rotation of Young Massive Star Clusters in a Simulated Dwarf Starburst

Abstract

We analyze the three-dimensional shapes and kinematics of the young star cluster population forming in a high-resolution griffin project simulation of a metal-poor dwarf galaxy starburst. The star clusters, which follow a power-law mass distribution, form from the cold ISM phase with an IMF sampled with individual stars down to 4 solar masses at sub-parsec spatial resolution. Massive stars and their important feedback mechanisms are modelled in detail. The simulated clusters follow a surprisingly tight relation between the specific angular momentum and mass with indications of two sub-populations. Massive clusters (M cl 3 × 10 4 M ) have the highest specific angular momenta at low ellipticities ( ∼ 0.2) and show alignment between their shapes and rotation. Lower mass clusters have lower specific angular momenta with larger scatter, show a broader range of elongations, and are typically misaligned indicating that they are not shaped by rotation. The most massive clusters (M 10 5 M ) accrete gas and proto-clusters from a 100 pc scale local galactic environment on a t 10 Myr timescale, inheriting the ambient angular momentum properties. Their two-dimensional kinematic maps show ordered rotation at formation, up to v ∼ 8.5 kms −1 , consistent with observed young massive clusters and old globular clusters, which they might evolve into. The massive clusters have angular momentum parameters λ R 0.5 and show Gauss-Hermite coefficients h 3 that are anticorrelated with the velocity, indicating asymmetric line-of-sight velocity distributions as a signature of a dissipative formation process.

STARFORGE: Towards a comprehensive numerical model of star cluster formation and feedback

“…(ii) Follow stellar dynamics: SF simulations that do not integrate stellar orbits explicitly generally discretize the stellar mass formed into a collisionless fluid represented by gravitationally softened particles (e.g. Grudić et al 2018a;Lahén et al 2019;Li et al 2019), which can produce qualitatively correct star cluster density profiles (Grudić et al 2018b;Lahén et al 2020), but have the severe limitation that the collisionless description (and phase-space density conservation) breaks down on mass scales M ࣠ 100 M , so if cluster formation is a hierarchical assembly from smaller masses (e.g. Bonnell, Bate & Vine 2003), then individual stellar dynamics is always important at some stage in the process.…”

The rotation of selected globular clusters and the differential rotation of M3 in multiple populations from the SDSS-IV APOGEE-2 survey

“…Orbital motions may be isotropic even during the formation of GCs, for example Lahén et al (2020) have argued that the massive clusters are isotropic already during their first 100 Myr after formation. Moreover, as Lane et al (2010) and has shown, the interaction between the cluster and the galactic tidal field combined within the internal dynamics could produce complex kinematical features, e.g.…”

A panchromatic view of star cluster formation in a simulated dwarf galaxy starburst

“…Here we aim to process the simulation output to match the data typically used in observational studies of young star clusters, and analyse the results using observationally verified methods. In Section 2 we first briefly introduce the simulation setup that has been extensively discussed in Lahén et al (2019), Lahén et al (2020a) and Lahén et al (2020b). In Section 3 we describe the post-processing and data reduction methods, including the radiative transfer modelling, synthetic photometry and star cluster detection.…”