The fractal dimension of star-forming regions at different spatial scales in M33

Abstract

We study the distribution of stars, HII regions, molecular gas, and individual giant molecular clouds in M33 over a wide range of spatial scales. The clustering strength of these components is systematically estimated through the fractal dimension. We find scale-free behavior at small spatial scales and a transition to a larger correlation dimension (consistent with a nearly uniform distribution) at larger scales. The transition region lies in the range 500-1000 pc. This transition defines a characteristic size that separates the regime of small-scale turbulent motion from that of large-scale galactic dynamics. At small spatial scales, bright young stars and molecular gas are distributed with nearly the same three-dimensional fractal dimension (Df <= 1.9), whereas fainter stars and HII regions exhibit higher values (Df = 2.2-2.5). Our results indicate that the interstellar medium in M33 is on average more fragmented and irregular than in the Milky Way.

18 pages including 4 figures. Accepted for publication in ApJ

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• Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters
• Characterizing gravitational instability in turbulent multi-component galactic discs
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• The long-term centimeter variability of active galactic nuclei: A new relation between variability timescale and accretion rate
• Hierarchy and size distribution function of star formation regions in the spiral galaxy NGC 628
• New Galactic embedded clusters and candidates from a WISE Survey
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