Future Trends in Computing

Añez

et al. 2010

ApJ

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 (D f,3D 1.9), whereas fainter stars and HII regions exhibit higher values D f,3D ≃ 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.

Section: Introductionmentioning

confidence: 99%

The Fractal Dimension of Star-Forming Regions at Different Spatial Scales in M33

Añez

et al. 2010

ApJ

“…The distribution of stars and star-forming regions also exhibits a spatial hierarchy from large star complexes to individual clusters (Efremov 1995;de la Fuente Marcos & de la Fuente Marcos 2006Elias et al 2009;Elmegreen 2010). This hierarchical structure is presumably a direct consequence of the fact that stars are formed in a medium with an underlying fractal structure (previous Section).…”

Section: Fractal Dimension Of Young Stellar Clustersmentioning

confidence: 97%

“…It appears that the distribution of gas and dust in these clouds determines the initial conditions of a newborn cluster because star formation follows the patterns defined by the densest regions (Bonnell et al 2003). Thus, the fractal (self-similar) distribution of the gas in molecular cloud complexes may account for the hierarchical structure observed in some open clusters (Elmegreen 2010). However, observations show that the morphologies of young clusters show a wide variety, from hierarchical to centrally condensed ones, often being elongated or surrounded by a low-density stellar halo (see, for example, Maíz-Apellániz 2001;Hartmann 2002;and Caballero 2008).…”

Section: Introductionmentioning

confidence: 99%

Internal Structure of Stellar Clusters: Geometry of Star Formation

2010

Proc. IAU

Abstract. The study of the internal structure of star clusters provides important clues concerning their formation mechanism and dynamical evolution. There are both observational and numerical evidences indicating that open clusters evolve from an initial clumpy structure, presumably a direct consequence of the formation in a fractal medium, toward a centrally condensed state. This simple picture has, however, several drawbacks. There can be very young clusters exhibiting radial patterns maybe reflecting the early effect of gravity on primordial gas. There can be also very evolved clusters showing fractal patterns that either have survived through time or have been generated subsequently by some (unknown) mechanism. Additionally, the fractal structure of some open clusters is much clumpier than the average structure of the interstellar medium in the Milky Way, although in principle a very similar structure should be expected. Here we summarize and discuss observational and numerical results concerning this subject.

“…Fractal clouds are known to be a good representation of star forming regions (Sanchez et al 2007a,b;Elmegreen 2002Elmegreen , 2010. These kinds of clouds are easy to construct by means of recurrence procedures that produce hierarchical self-similar mass distributions.…”

Section: Fractal Cloudsmentioning

confidence: 99%

The Dependence of Prestellar Core Mass Distributions on the Structure of the Parental Cloud

Parravano

2012

ApJ

The mass distribution of prestellar cores is obtained for clouds with arbitrary internal mass distributions using a selection criterion based on the thermal and turbulent Jeans mass and applied hierarchically from small to large scales. We have checked this methodology comparing our results for a lognormal density PDF with the theoretical CMF derived by Hennebelle & Chabrier, namely a power-law at large scales and a log-normal cutoff at low scales, but our method can be applied to any mass distributions representing a star-forming cloud. This methodology enables us to connect the parental cloud structure with the mass distribution of the cores and their spatial distribution, providing an efficient tool for investigating the physical properties of the molecular clouds that give rise to the prestellar core distributions observed. Simulated fBm clouds with the Hurst exponent close to the value H = 1/3 give the best agreement with the theoretical CMF derived by Hennebelle & Chabrier and Chabrier's system IMF. Likewise, the spatial distribution of the cores derived from our methodology show a surface density of companions compatible with those observed in Trapezium and Ophiucus star-forming regions. This method also allows us to analyze the properties of the mass distribution of cores for different realizations. We found that the variations in the number of cores formed in different realizations of fBm clouds (with the same Hurst exponent) are much larger than the expected root N statistical fluctuations, increasing with H.