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Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation

Arnold, Becky; Wright, Nicholas; Parker, Richard J.

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Authors

Becky Arnold

Richard J. Parker



Abstract

We investigate whether spatial-kinematic substructure in young star-forming regions can be quantified using Moran's $I$ statistic. Its presence in young star clusters would provide an indication that the system formed from initially substructured conditions, as expected by the hierarchical model of star cluster formation, even if the cluster were spatially smooth and centrally concentrated. Its absence, on the other hand, would be evidence that star clusters form monolithically. The Moran's $I$ statistic is applied to $N$-body simulations of star clusters with different primordial spatial-velocity structures, and its evolution over time is studied. It is found that this statistic can be used to reliably quantify spatial-kinematic substructure, and can be used to provide evidence as to whether the spatial-kinematic structure of regions with ages $\lesssim$ 6 Myr is best reproduced by the hierarchical or monolithic models of star formation. Moran's $I$ statistic is also able to conclusively say whether the data are $not$ consistent with initial conditions that lack kinematic substructure, such as the monolithic model, in regions with ages up to, and potentially beyond, 10 Myrs. This can therefore provide a kinematic signature of the star cluster formation process that is observable for many Myr after any initial spatial structure has been erased.

Citation

Arnold, B., Wright, N., & Parker, R. J. (2022). Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation. Monthly Notices of the Royal Astronomical Society, 515(2), 2266–2279. https://doi.org/10.1093/mnras/stac1955

Journal Article Type Article
Acceptance Date Jul 7, 2022
Online Publication Date Jul 11, 2022
Publication Date 2022-09
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 515
Issue 2
Pages 2266–2279
DOI https://doi.org/10.1093/mnras/stac1955
Keywords Astrophysics of Galaxies; Solar and Stellar Astrophysics
Publisher URL https://academic.oup.com/mnras/article-abstract/515/2/2266/6639889?redirectedFrom=fulltext

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