The Long-term Evolution of Star Clusters Formed with a Centrally Peaked Star Formation Efficiency Profile

Shukirgaliyev, Bekdaulet and Parmentier, Geneviève and Just, Andreas and Berczik, Péter (2018) The Long-term Evolution of Star Clusters Formed with a Centrally Peaked Star Formation Efficiency Profile. ASTROPHYSICAL JOURNAL, 863. ISSN 1538-4357

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Abstract

We have studied the long-term evolution of star clusters of the solar neighborhood, starting from their birth in gaseous clumps until their complete dissolution in the Galactic tidal field. We have combined the “local-density-driven cluster formation model” of Parmentier & Pfalzner with direct N-body simulations of clusters following instantaneous gas expulsion. We have studied the relation between cluster dissolution time, t dis, and cluster “initial” mass, M init, defined as the cluster mass at the end of the dynamical response to gas expulsion (i.e., violent relaxation), when the cluster age is 20-30 Myr. We consider the “initial” mass to be consistent with other works that neglect violent relaxation. The model clusters formed with a high star formation efficiency (SFE, i.e., gas mass fraction converted into stars) follow a tight mass-dependent relation, in agreement with previous theoretical studies. However, the low-SFE models present a large scatter in both the “initial” mass and the dissolution time, a shallower mass-dependent relation than high-SFE clusters, and most dissolve within 1 Gyr (cluster teenage mortality). Both groups differ in their structural properties on average. Combining two populations of clusters, high- and low-SFE ones, with domination of the latter, yields a cluster dissolution time for the solar neighborhood in agreement with that inferred from observations, without any additional destructive processes such as giant molecular cloud encounters. An apparent mass-independent relation may emerge for our low-SFE clusters when we neglect low-mass clusters (as expected for extragalactic observations), although more simulations are needed to investigate this aspect.

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