Journal Article

The evolution of stellar structures in dwarf galaxies

N. Bastian, D. R. Weisz, E. D. Skillman, K. B. W. McQuinn, A. E. Dolphin, R. A. Gutermuth, J. M. Cannon, B. Ercolano, M. Gieles, R. C. Kennicutt and F. Walter

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 1539-1551
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17841.x
The evolution of stellar structures in dwarf galaxies

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We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour–magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select blue helium burning stars, which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young (≲10 Myr) population of OB stars for a subset of the galaxies based on the tip of the young main sequence. By selecting stars in different age ranges, we can then study how the spatial distribution of these stars evolves with time. We find, in agreement with previous studies, that stars are born within galaxies with a high degree of substructure which is made up of a continuous distribution of clusters, groups and associations from parsec to hundreds of parsec scales. These structures disperse on time-scales of tens to hundreds of Myr, which we quantify using the two-point correlation function and the Q-parameter developed by Cartwright & Whitworth. On galactic scales, we can place lower limits on the time it takes to remove the original structure (i.e. structure survives for at least this long), tevo, which varies between ∼100 Myr (NGC 2366) and ∼350 Myr (DDO 165). This is similar to what we have found previously for the Small Magellanic Cloud (∼80 Myr) and the Large Magellanic Cloud (∼175 Myr). We do not find any strong correlations between tevo and the luminosity of the host galaxy.

Keywords: galaxies: dwarf; galaxies: individual: DDO 165; galaxies: individual: Holmberg II; galaxies: individual: IC 2574; galaxies: individual: NGC 784; galaxies: individual: NGC 2366

Journal Article.  8560 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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