W. J. Maciel -
Abstract #117
THE ABUNDANCE GRADIENT IN GALACTIC HII REGIONS
R. T. Rood, C. Quireza, T. M. Bania, D. S. Balser, W. J. Maciel
From Stars to Galaxies: Building the Pieces to Build Up the Universe, ASP Conference Series, Vol. 374, Ed. A. Vallenari, R. Tantalo, L. Portinari, A. Moretti, 169-174 (2007) We derive the electron temperature gradient in the Galactic disk using a sample of Hii regions that spans Galactocentric distances 0–17 kpc. The electron temperature was calculated using high precision radio recombina- tion line and continuum observations for more than 100 Hii regions. The large number of nebulae widely distributed over the Galactic disk together with the uniformity of our data provide a secure estimate of the present electron tem- perature gradient in the Milky Way. Because metals are the main coolants in the photoionized gas, the electron temperature along the Galactic disk should be directly related to the distribution of heavy elements in the Milky Way. Our derived abundance gradient is considerably flatter than the oft cited value of Shaver et al. (1983) (S83). There are no significant variations in the value of the gradient as a function of Galactocentric radius or azimuth. The scatter we find in the Hii region electron temperatures at a given Galactocentric radius is not due to observational error, but rather to intrinsic fluctuations in these tem- peratures which are almost certainly due to fluctuations in the nebular heavy element abundances.
