No evidence of mass segregation in massive young clusters

¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal e-mail: jascenso@astro.up.pt
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Calar Alto Observatory – Centro Astronómico Hispano-Alemán, C/ Jesús Durbán Remón 2-2, 04004 Almeria, Spain
⁴ Departamento de Matemática Aplicada da Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 657, 4169-007 Porto, Portugal

Received: 1 April 2008
Accepted: 17 November 2008

Abstract

Aims. We investigate the validity of the mass segregation indicators commonly used in analysing young stellar clusters.

Methods. We simulate observations by constructing synthetic seeing-limited images of a 1000 massive clusters (10⁴ ) with a standard IMF and a King-density distribution function.

Results. We find that commonly used indicators are highly sensitive to sample incompleteness in observational data and that radial completeness determinations do not provide satisfactory corrections, rendering the studies of radial properties highly uncertain. On the other hand, we find that, under certain conditions, the global completeness can be estimated accurately, allowing for the correction of the global luminosity and mass functions of the cluster.

Conclusions. We argue that there is currently no observational evidence of mass segregation in young compact clusters since there is no robust way to differentiate between true mass segregation and sample incompleteness effects. Caution should then be exercised when interpreting results from observations as evidence of mass segregation.