Journal Article

On the fraction of star clusters surviving the embedded phase

Q. E. Goddard, N. Bastian and R. C. Kennicutt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 405, issue 2, pages 857-869
Published in print June 2010 | ISSN: 0035-8711
Published online June 2010 | e-ISSN: 1365-2966 | DOI:
On the fraction of star clusters surviving the embedded phase

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In this paper we derive ages and masses for 276 clusters in the merger galaxy NGC 3256. This was achieved by taking accurate photometry in four wavebands from archival Hubble Space Telescope images. Photometric measurements are compared to synthetic stellar population (SSP) models to find the most probable age, mass and extinction. The cluster population of NGC 3256 reveals an increase in the star formation rate (SFR) over the last 100 Myr and the initial cluster mass function (ICMF) is best described by a power-law relation with slope α= 1.85 ± 0.12.

Using the observed cluster population for NGC 3256 we calculate the implied mass of clusters younger than 10-Myr old, and convert this to a cluster formation rate over the last 10 Myr. Comparison of this value with the SFR indicates the fraction of stars found within bound clusters after the embedded phase of cluster formation, Γ, is 22.9 ±7.39.8 per cent for NGC 3256. We carried out an in-depth analysis into the errors associated with such calculations showing that errors introduced by the SSP fitting must be taken into account and an unconstrained metallicity adds to these uncertainties. Observational biases should also be considered.

Using published cluster population data sets we calculate Γ for six other galaxies and examine how Γ varies with environment. We show that Γ increases with the SFR density and can be described as a power-law type relation of the form Γ (per cent) = (29.0 ± 6.0) Σ0.24±0.04SFR (M yr−1 kpc−2).

Keywords: stars: formation; galaxies: stellar content; galaxies: structure

Journal Article.  11627 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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