The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449 - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449 - Astrophysics > Cosmology and Nongalactic Astrophysics - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Abstract: Using ACS-HST images to yield continuum subtracted photometric maps inH\alpha of the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, weproduced extensive over 2000 regions for M51, over 200 regions for NGC4449catalogues of parameters of their HII regions: their H\alpha luminosities,equivalent radii and coordinates with respect to the galaxy centers. From thesedata we derived, for each region, its mean luminosity weighted electrondensity, , determined from the H\alpha luminosity and the radius, R, ofthe region. Plotting these densities against the radii of the regions we findexcellent fits for varying as R^{-1-2}. This relatively simple relationhas not, as far as we know, been predicted from models of HII region structure,and should be useful in constraining future models. Plotting the densitiesagainst the galactocentric radii, r, of the regions we find good exponentialfits, with scale lengths of close to 10 kpc for both galaxies. These values arecomparable to the scale lengths of the HI column densities for both galaxies,although their optical structures, related to their stellar components are verydifferent. This result indicates that to a first approximation the HII regionscan be considered in pressure equilibrium with their surroundings. We also plotthe electron density of the HII regions across the spiral arms of M51, showingan envelope which peaks along the ridge lines of the arms.



Autor: Leonel Gutiérrez, John E. Beckman

Fuente: https://arxiv.org/







Documentos relacionados