Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-08-28
Astronomy and Astrophysics
Astrophysics
accepted for publication in AJ
Scientific paper
10.1086/319949
We measure reddenings to HII regions in NGC 2903, NGC 1512, M51, NGC 4449 and NGC 6946 from Hubble Space Telescope Pa alpha and H alpha images. Extinctions range from A_V ~ 5 - 0 depending upon the galaxy. For the galaxies with HST images in both lines, NGC 2903, NGC 1512 and M51, the Pa alpha and H alpha emission are almost identical in morphology which implies that little emission from bright HII regions is hidden from view by regions of comparatively high extinction. The scatter in the measured extinctions is only +- 0.5 mag. We compare the reddenings we measure in five galaxies using the Pa alpha to H alpha ratios to those measured previously from the Balmer decrement in the LMC and as a function of radius in M101 and M51. We find that luminosity weighted mean extinctions of these ensembles of HI regions are correlated with gas surface density and metallicity. The correlation is consistent with the mean extinction depending on dust density where the dust to gas mass ratio scales with the metallicity. This trend is expected if HII regions tend to be located near the mid-plane of a gas disk and emerge from their parent molecular clouds soon after birth. In environments with gas densities below a few hundred Msol/pc^2 star formation rates estimated from integrated line fluxes and mean extinctions are likely to be fairly accurate.
Quillen Alice. C.
Yukita Mihoko
No associations
LandOfFree
A comparison between Pa alpha and H alpha emission: The relation between HII region mean reddening, local gas density and metallicity 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 A comparison between Pa alpha and H alpha emission: The relation between HII region mean reddening, local gas density and metallicity, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A comparison between Pa alpha and H alpha emission: The relation between HII region mean reddening, local gas density and metallicity will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-268573