Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-08-14
Astronomy and Astrophysics
Astrophysics
10 pages, 2 embedded postscript files, 3 jpeg images; accepted for publication in ApJ Letters
Scientific paper
10.1086/311626
We present deep Halpha images of three nearby late-type spiral galaxies (NGC628, NGC1058 and NGC6946), which reveal the presence of HII regions out to, and beyond, two optical radii (defined by the 25th B-band isophote). The outermost HII regions appear small, faint and isolated, compared to their inner disk counterparts, and are distributed in organized spiral arm structures, likely associated with underlying HI arms and faint stellar arms. The relationship between the azimuthally--averaged Halpha surface brightness (proportional to star formation rate per unit area) and the total gas surface density is observed to steepen considerably at low gas surface densities. We find that this effect is largely driven by a sharp decrease in the covering factor of star formation at large radii, and not by changes in the rate at which stars form locally. An azimuthally--averaged analysis of the gravitational stability of the disk of NGC6946 reveals that while the existence of star formation in the extreme outer disk is consistent with the Toomre-Q instability model, the low rates observed are only compatible with the model when a constant gaseous velocity dispersion is assumed. We suggest that observed behaviour could also be explained by a model in which the star formation rate has an intrinsic dependence on the azimuthally-averaged gas volume density, which decreases rapidly in the outer disk due to the vertical flaring of the gas layer.
Ferguson Annette
Gallagher John Jay
Hunter Deidre
Wyse Rosemary
No associations
LandOfFree
Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies 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 Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-384206