THE GALAXY-WIDE DISTRIBUTIONS OF MEAN ELECTRON DENSITY IN THE H II REGIONS OF M51 AND NGC 4449

Journal Article · Wed Feb 10 04:00:00 EST 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/710/1/L44; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21301316

Gutierrez, Leonel ^[1]

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1. Universidad Nacional Autonoma de Mexico, Instituto de AstronomIa, Ensenada, B. C. (Mexico)

Using Advanced Camera for Surveys-Hubble Space Telescope images to yield continuum-subtracted photometric maps in H{alpha} of the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, we produced extensive (over 2000 regions for M51 and over 200 regions for NGC 4449) catalogs of parameters of their H II regions: their H{alpha} luminosities, equivalent radii, and coordinates with respect to the galaxy centers. From these data we derived, for each region, its mean luminosity-weighted electron density, (n{sub e} ), determined from the H{alpha} luminosity and the radius, R, of the region. Plotting these densities against the radii of the regions, we find excellent fits for (n{sub e} ) varying as R {sup -1/2}. This relatively simple relation has not, as far as we know, been predicted from models of H II region structure, and should be useful in constraining future models. Plotting the densities against the galactocentric radii, r, of the regions, we find good exponential fits with scale lengths of close to 10 kpc for both galaxies. These values are comparable to the scale lengths of the H I column densities for both galaxies, although their optical structures, related to their stellar components, are very different. This result indicates that to a first approximation the H II regions can be considered in pressure equilibrium with their surroundings. We also plot the electron density of the H II regions across the spiral arms of M51, showing an envelope which peaks along the ridgelines of the arms.

• OSTI ID: 21301316
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 710; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
99 GENERAL AND MISCELLANEOUS
APPROXIMATIONS
CAMERAS
CATALOGS
COORDINATES
ELECTRON DENSITY
GALAXIES
LUMINOSITY
TELESCOPES