The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449

Details The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449 The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449

2010-01-02

arxiv.org/abs/1001.0276v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

Accepted for publication in ApJ Letters. 5 pages, 5 figures. Formatted with emulateapj

Scientific paper

Using ACS-HST 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, over 200 regions for NGC4449) catalogues of parameters of their HII 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, , 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 varying as R^{-1/2}. This relatively simple relation has not, as far as we know, been predicted from models of HII 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 HI 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 HII regions can be considered in pressure equilibrium with their surroundings. We also plot the electron density of the HII regions across the spiral arms of M51, showing an envelope which peaks along the ridge lines of the arms.

Affiliated with

Also associated with

No associations

Rating

The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449 will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-233867