# Comparisons between different techniques for measuring mass segregation

Parker, RJ and Goodwin, SP (2015) Comparisons between different techniques for measuring mass segregation. Monthly Notices of the Royal Astronomical Society, 449 (4). pp. 3381-3392. ISSN 0035-8711

## Abstract

We examine the performance of four different methods which are used to measure mass segregation in star-forming regions: the radial variation of the mass function $\mathcal{M}_{\rm MF}$; the minimum spanning tree-based $\Lambda_{\rm MSR}$ method; the local surface density $\Sigma_{\rm LDR}$ method; and the $\Omega_{\rm GSR}$ technique, which isolates groups of stars and determines whether the most massive star in each group is more centrally concentrated than the average star. All four methods have been proposed in the literature as techniques for quantifying mass segregation, yet they routinely produce contradictory results as they do not all measure the same thing. We apply each method to synthetic star-forming regions to determine when and why they have shortcomings. When a star-forming region is smooth and centrally concentrated, all four methods correctly identify mass segregation when it is present. However, if the region is spatially substructured, the $\Omega_{\rm GSR}$ method fails because it arbitrarily defines groups in the hierarchical distribution, and usually discards positional information for many of the most massive stars in the region. We also show that the $\Lambda_{\rm MSR}$ and $\Sigma_{\rm LDR}$ methods can sometimes produce apparently contradictory results, because they use different definitions of mass segregation. We conclude that only $\Lambda_{\rm MSR}$ measures mass segregation in the classical sense (without the need for defining the centre of the region), although $\Sigma_{\rm LDR}$ does place limits on the amount of previous dynamical evolution in a star-forming region.

Item Type: Article This is a pre-copy edited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review.The version of record MNRAS (June 01, 2015) 449 (4): 3381-3392. is available online at: http://dx.doi.org/10.1093/mnras/stv539 astro-ph.GA; astro-ph.GA; astro-ph.SR Q Science > QB Astronomy Astrophysics Research Institute Oxford University Press Author 18 Mar 2015 14:21 16 Sep 2018 20:39 http://researchonline.ljmu.ac.uk/id/eprint/766