The Young Massive Star Cluster Westerlund 2 Observed with MUSE. III. A Cluster in Motion—The Complex Internal Dynamics

Zeidler, Peter; Sabbi, E.; Nota, A.; McLeod, Anna F.

doi:10.3847/1538-3881/abd6ca

Cited by 13 publications

(38 citation statements)

References 82 publications

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“…One possible explanation for the deficit of high mass stars is dynamical interactions that preferentially eject massive members (see Oh & Kroupa 2016). This is supported by recent observations finding a significant number of "runaway" O and B stars ejected from young star clusters (Lennon et al 2018;Zeidler et al 2021). In our simulations we find no evidence that high-mass stars are preferentially ejected.…”

Section: Cluster Assembly and Dynamical Effectssupporting

confidence: 85%

Cluster assembly and the origin of mass segregation in the STARFORGE simulations

Guszejnov

Markey

Offner

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Stars form in dense, clustered environments, where feedback from newly formed stars eventually ejects the gas, terminating star formation and leaving behind one or more star clusters. Using the STARFORGE simulations, it is possible to simulate this process in its entirety within a molecular cloud, while explicitly evolving the gas radiation and magnetic fields and following the formation of individual, low-mass stars. We find that individual star-formation sites merge to form ever larger structures, while still accreting gas. Thus clusters are assembled through a series of mergers. During the cluster assembly process a small fraction of stars are ejected from their clusters; we find no significant difference between the mass distribution of the ejected stellar population and that of stars inside clusters. The star-formation sites that are the building blocks of clusters start out mass segregated with one or a few massive stars at their center. As they merge the newly formed clusters maintain this feature, causing them to have mass-segregated substructures without themselves being centrally condensed. The merged clusters relax to a centrally condensed mass segregated configuration through dynamical interactions between their members, but this process does not finish before feedback expels the remaining gas from the cluster. In the simulated runs the gas-free clusters then become unbound and breakup. We find that turbulent driving and a periodic cloud geometry can significantly reduce clustering and prevent gas expulsion. Meanwhile, the initial surface density and level of turbulence have little qualitative effect on cluster evolution, despite the significantly different star formation histories.

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Section: Cluster Assembly and Dynamical Effectssupporting

confidence: 85%

Cluster assembly and the origin of mass segregation in the STARFORGE simulations

Guszejnov

Markey

Offner

et al. 2022

Monthly Notices of the Royal Astronomical Society

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“…Work by Zeidler et al (2021) has made a detailed case for the systemic heliocentric radial velocity of Westerlund 2 being 15.9 km s −1 , with an error in the region of 1 km s −1 (see their Fig. 3).…”

Section: Westerlund 2 In Its Settingmentioning

confidence: 99%

Radial velocities from far red spectra of Carina Arm O and early B stars

Drew¹,

Parsons²,

Mohr-Smith³

2022

Preprint

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Massive O and early B stars are important markers of recent star formation and exert a significant influence on their environments during their short lives via photoionization and winds and when they explode as supernovae. In the Milky Way they can be detected at great distances but often lie behind large dust columns, making detection at short wavelengths difficult. In this study the use of the less extinguished far-red spectrum (8400 -8800 Å) for radial velocity measurement is examined. Results are reported for a sample of 164 confirmed OB stars within a 2-degree field positioned on the Carina Arm. Most stars are at distances between 3 and 6 kpc, and Westerlund 2 is at the field edge. The measured radial velocities have errors concentrated in the 3-10 km s −1 range, with a systematic uncertainty of 2-3 km s −1 . These are combined with Gaia-mission astrometry to allow full space motions to be constructed. Up to 22 stars are likely to be runaways although 8 of them are as likely to be interloping (so far undetected) binaries. The mean azimuthal motion of the sample fits in with recent measurements of Galactic disk rotation. In the Galactocentric radial direction the mean motion indicates modest infall at a speed of ∼ 10 km s −1 . This experiment shows that weak Paschen lines in the far-red can yield credible radial velocity determination, offering the prospect of exploring OB-star kinematics over much more of the Galactic disk than has hitherto been possible.

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“…Observations support this formation mechanism as well. For example, a study of radial velocities of different stellar populations in the star cluster Westerlund 2 shows two distinct clumps on route to merging in the near future (Zeidler et al 2021). Fujii et al (2012) also showed that the existence of runaway stars around the young cluster R136 could be explained through prompt subcluster mergers in a time frame of 3 Myr.…”

Section: Introductionmentioning

confidence: 99%

Modelling Star Cluster Formation: Mergers

Karam,

Sills

2022

Preprint

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Star cluster formation in giant molecular clouds involves the local collapse of the cloud into small gas-rich subclusters, which can then subsequently collide and merge to build up the final star cluster(s). In this paper, we simulate collisions between these subclusters, using coupled smooth particle hydrodynamics for the gas and N-body dynamics for the stars. We are guided by previous radiation hydrodynamics simulations of molecular cloud collapse which provide the global properties of the colliding clusters, such as their stellar and gas masses, and their initial positions and velocities. The subclusters in the original simulation were treated as sink particles which immediately merged into a single entity after the collision. We show that the more detailed treatment provides a more complex picture. At collisional velocities above ≈ 10 km/s, the stellar components of the cluster do not form a monolithic cluster within 3 Myr, although the gas may do so. At lower velocities, the clusters do eventually merge but over timescales that may be longer than the time for a subsequent collision. The structure of the resultant cluster is not well-fit by any standard density distribution, and the clusters are not in equilibrium but continue to expand over our simulation time. We conclude that the simple sink particle treatment of subcluster mergers in large-scale giant molecular cloud simulations provides an upper limit on the final cluster properties.

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The Young Massive Star Cluster Westerlund 2 Observed with MUSE. III. A Cluster in Motion—The Complex Internal Dynamics

Cited by 13 publications

References 82 publications

Cluster assembly and the origin of mass segregation in the STARFORGE simulations

Cluster assembly and the origin of mass segregation in the STARFORGE simulations

Radial velocities from far red spectra of Carina Arm O and early B stars

Modelling Star Cluster Formation: Mergers

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