SCYON Abstract

Received on December 1 2010

Hierarchical Stellar Structures in the Local Group Dwarf Galaxy NGC 6822

AuthorsGouliermis Dimitrios A. (1), Schmeja Stefan (2), Klessen Ralf S. (2), de Blok W. J. G. (3), and Walter Fabian (1)
Affiliation(1) Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany
(2) Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
(3) University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;
Accepted byAstrophysical Journal
Contactdgoulier@mpia.de
URLhttp://adsabs.harvard.edu/abs/2010arXiv1010.1940G
Links

Abstract

We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages <~ 500 Myr in the Local Group dwarf irregular galaxy NGC 6822. Our observational material comprises the most complete optical stellar catalog of the galaxy from imaging with the Suprime-Cam at the 8.2-m SUBARU Telescope. We identify 47 distinct star clusters with the application of the nearest-neighbor density method to this catalog for a detection threshold of 3sigma above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at ~ 68 pc. Their cluster mass function is fitted very well by a power-law with index alpha ~ 1.5 +/- 0.7, consistent with other Local Group galaxies and the cluster initial mass function. The application of the nearest-neighbor density method for various density thresholds, other than 3sigma, enabled the identification of stellar concentrations in various length-scales. The stellar density maps constructed with this technique provide a direct proof of hierarchically structured stellar concentrations in NGC 6822. We illustrate this hierarchy by the so-called "dendrogram" of the detected stellar structures, which demonstrates that most of the detected structures split up into several substructures over at least three levels. We quantify the hierarchy of these structures with the use of the minimum spanning tree method. The morphological hierarchy in stellar clustering, which we observe in NGC 6822 resembles that of the turbulent interstellar matter, suggesting that turbulence on pc- and kpc-scales has been probably the major agent that regulated clustered star formation in NGC 6822.