On the Fractal Distribution of HII Regions in Disk Galaxies
نویسندگان
چکیده
In this work we quantify the degree to which star-forming events are clumped. We apply a precise and accurate technique to calculate the correlation dimension Dc of the distribution of HII regions in a sample of disk galaxies. Our reliable results are distributed in the range 1.5 ∼< Dc ∼< 2.0. We get significant variations in the fractal dimension among galaxies, contrary to a universal picture sometimes claimed in literature. The faintest galaxies tend to distribute their HII regions in more clustered (less uniform) patterns. Moreover, the fractal dimension for the brightest HII regions within the same galaxy seems to be smaller than for the faintest ones suggesting some kind of evolutionary effect.
منابع مشابه
The Fractal Distribution of HII Regions in Disk Galaxies
It is known that the gas has a fractal structure in a wide range of spatial scales with a fractal dimension that seems to be a constant around Df ≃ 2.7. It is expected that stars forming from this fractal medium exhibit similar fractal patterns. Here we address this issue by quantifying the degree to which starforming events are clumped. We develop, test, and apply a precise and accurate techni...
متن کاملDiffuse Ionized Gas in Spiral Galaxies: Probing Lyman Continuum Photon Leakage from Hii Regions?
As part of a large study to map the distribution of star formation across galactic disks, we have obtained deep Hα images of the nearby Sculptor Group spirals NGC 247 and NGC 7793. These images are of sufficiently high quality that they allow identification and analysis of diffuse Hα emission at surface brightness levels ranging from those of extremely low density HII regions to those of the lo...
متن کاملThe Extreme Outer Regions of Disk Galaxies: I. Chemical Abundances of Hii Regions
We present the first results of an ongoing project to investigate the present-day chemical abundances of the extreme outer parts of galactic disks, as probed by the emission line spectra of a new sample of HII regions. The galaxies studied here, NGC 628, NGC 1058 and NGC 6946, are all late-type spiral galaxies, characterized by larger than average HI-to-optical sizes. Our deep Hα images have re...
متن کاملA Pressure Anomaly for HII Regions in Irregular Galaxies
The pressures of giant HII regions in 6 dwarf Irregular galaxies are found to be a factor of ∼ 10 larger than the average pressures of the corresponding galaxy disks, obtained from the stellar and gaseous column densities. This is unlike the situation for spiral galaxies where these two pressures are approximately equal. Either the HII regions in these dwarfs are all so young that they are stil...
متن کاملSample of minor merger of galaxies : Optical CCD surface photometry and HII region properties
We present the results of the B, V and I photometry of eleven southern minor mergers. The total apparent B magnitude, integrated B-V and V-I colours were measured. We built B, V, and I equivalent profiles for each galaxy and decomposed them into bulge and disk components when possible. From Hα+N[II] images we have estimated the basic photometric parameters of the HII regions, such as position, ...
متن کامل