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

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.Comment: 18 pages including 4 figures. Accepted for publication in Ap

The Correlation Dimension of Young Stars in Dwarf Galaxies

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 $1.68\pm0.14$ to $0.10\pm0.05$ 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.Comment: 25 pages, 10 figures, accepted by A

On the Disruption of Star Clusters in a Hierarchical Interstellar Medium

The distribution of the number of clusters as a function of mass M and age T suggests that clusters get eroded or dispersed in a regular way over time, such that the cluster number decreases inversely as an approximate power law with T within each fixed interval of M. This power law is inconsistent with standard dispersal mechanisms such as cluster evaporation and cloud collisions. In the conventional interpretation, it requires the unlikely situation where diverse mechanisms stitch together over time in a way that is independent of environment or M. Here we consider another model in which the large scale distribution of gas in each star-forming region plays an important role. We note that star clusters form with positional and temporal correlations in giant cloud complexes, and suggest that these complexes dominate the tidal force and collisional influence on a cluster during its first several hundred million years. Because the cloud complex density decreases regularly with position from the cluster birth site, the harassment and collision rates between the cluster and the cloud pieces decrease regularly with age as the cluster drifts. This decrease is typically a power law of the form required to explain the mass-age distribution. We reproduce this distribution for a variety of cases, including rapid disruption, slow erosion, combinations of these two, cluster-cloud collisions, cluster disruption by hierarchical disassembly, and partial cluster disruption. We also consider apparent cluster mass loss by fading below the surface brightness limit of a survey. In all cases, the observed log M - \log T diagram can be reproduced under reasonable assumptions.Comment: ApJ vol. 712, March 20, 2010, 33 pages 15 figure

The Spatial Evolution of Stellar Structures in the LMC/SMC

We present an analysis of the spatial distribution of various stellar populations within the Large and Small Magellanic Clouds. We use optically selected stellar samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC/SMC. We use two statistical techniques to study the evolution of structure within these galaxies, the $Q$-parameter and the two-point correlation function (TPCF). In both galaxies we find the stars are born with a high degree of substructure (i.e. are highly fractal) and that the stellar distribution approaches that of the 'background' population on timescales similar to the crossing times of the galaxy (~80/150 Myr for the SMC/LMC respectively). By comparing our observations to simple models of structural evolution we find that 'popping star clusters' do not significantly influence structural evolution in these galaxies. Instead we argue that general galactic dynamics are the main drivers, and that substructure will be erased in approximately the crossing time, regardless of spatial scale, from small clusters to whole galaxies. This can explain why many young Galactic clusters have high degrees of substructure, while others are smooth and centrally concentrated. We conclude with a general discussion on cluster 'infant mortality', in an attempt to clarify the time/spatial scales involved.Comment: 6 pages, conference contribution to IAU Symposium 256, van Loon J.T. & Oliviera J.M., ed

Kompleksi fibronektinskih fragmenata i imunoglobulina G u gingivalnoj tečnosti osoba obolelih od parodontopatije

Introduction Fibronectin (FN) can interact with immunoglobulin G (IgG) molecules affecting the process of physiological elimination and causing abnormal deposition of immune complexes. The aim of the study was to analyze interaction between FN fragments and IgG molecules with different glycosylation profiles in gingival crevicular fluid (GCF) of patients with periodontal disease and healthy controls. Material and Methods The study included 30 patients with moderate and advanced periodontitis and 22 healthy subjects. IgG and FN content in GCF were measured as well as the presence of FN and galactose expression on IgG molecules. Results IgG content in GCF was five times higher in patients with moderate (p lt 0.01) and eight time higher in patients with advanced periodontitis (p lt 0.001) compared to healthy subjects. Also, hypogalactosylated forms of IgG were found in higher concentration in GCF of patients with advanced periodontitis compared to moderate periodontitis and healthy subjects (p lt 0.05). FN fragments of molecular mass 48 - 53 kDa were the most commonly found fragments in all three groups. Furthermore, in patients with advanced periodontitis, fibronectin fragments were attached to IgG molecules. Conclusion IgG and FN fragments form complexes in GCF in patients with periodontal disease and healthy subjects.Uvod Fibronektin može da interreaguje s molekulima imunoglobulina G (IgG) i utiče na normalan klirens ili poremećeno deponovanje imunskih kompleksa. Cilj ovog rada je bio da se ispita veza između fibronektina i IgG različitih glikoformi u gingivalnoj tečnosti osoba obolelih od parodontopatije i parodontalno zdravih ispitanika. Materijal i metode rada U studiju je uključeno 30 pacijenata s umerenom i uznapredovalom parodontopatijom i 22 parodontalno zdrave osobe. U gingivalnoj tečnosti određivan je sadržaj IgG i fibronektina dot blot i imunoblot tehnikama. IgG iz gingivalnih tečnosti su afinitetno izolovani i analizirani na prisustvo fibronektina i ekspresiju galaktoze. Rezultati Sadržaj IgG u gingivalnoj tečnosti osoba s umerenom parodontopatijom bio je oko pet puta veći u odnosu na sadržaj IgG kod zdravih osoba (p lt 0,01), dok je kod uznapredovalih oblika bio oko osam puta veći (p lt 0,001). Takođe, hipogalaktozilovane forme IgG su većoj meri postojale kod osoba sa uznapredovalom parodontopatijom u odnosu na zdrave i osobe s umerenom parodontopatijom (p lt 0,05). U sve tri analizirane grupe dominirali su fibronektinski fragmenti od 48 do 53 kDa. Uočeno je da su IgG izolovani iz gingivalne tečnosti vezani za fragmente fibronektina, pri čemu su IgG osoba sa uznapredovalom parodontopatijom, imali najveću količinu ovih vezanih fragmenata. Zaključak Dobijeni rezultati pokazuju da IgG gingivalne tečnosti zdravih i osoba s parodontopatijom formiraju komplekse sa fibronektinom