The Correlation Dimension of Young Stars in Dwarf Galaxies

Abstract

We present the correlation dimension of resolved young stars in four actively star-forming dwarf galaxies that are sufficiently resolved and transparent to be modeled as projections of three-dimensional point distributions. We use data in the Hubble Space Telescope archive; photometry for one of them, UGCA 292, is presented here for the first time. We find that there are statistically distinguishable differences in the nature of stellar clustering among the sample galaxies. The young stars of VII Zw 403, the brightest galaxy in the sample, have the highest value for the correlation dimension and also the most dramatic decrease with logarithmic scale, falling from $1.68\pm 0.14$ to $0.10\pm 0.05$ over less than a factor of ten in $r$. This decrease is consistent with the edge effect produced by a projected Poisson distribution within a 2:2:1 ellipsoid. The young stars in UGC 4483, the faintest galaxy in the sample, exhibit very different behavior, with a constant value of about 0.5 over this same range in $r$, extending nearly to the edge of the distribution. This behavior may indicate either a scale-free distribution with an unusually low correlation dimension, or a two-component (not scale-free) combination of cluster and field stars.

arXiv comment25 pages, 10 figures, accepted by AJ

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• The Spatial Distribution of the Young Stellar Clusters in the Star Forming Galaxy NGC 628
• Hierarchical Star Formation in Nearby LEGUS Galaxies
• The fractal dimension of star-forming regions at different spatial scales in M33
• The Fractal Distribution of HII Regions in Disk Galaxies
• The Dependence of the Hierarchical Distribution of Star Clusters on Galactic Environment
• The Nature of the Gould Belt from a Fractal Analysis of its Stellar Population
• On the Dispersal of Young Stellar Hierarchies
• The Nature and Nurture of Star Clusters
• Reaching the oldest stars beyond the Local Group: ancient star formation in UGC 4483
• Fractal Measures and Nonlinear Dynamics of Overcontact Binaries