H II REGION METALLICITY DISTRIBUTION IN THE MILKY WAY DISK

Journal Article · Thu Sep 01 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/1/27· OSTI ID:21582956

Balser, Dana S ^[1]; Rood, Robert T ^[2]; Bania, T M; Anderson, L D ^[3]

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1. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
2. Astronomy Department, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)
3. Institute for Astrophysical Research, Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)

The distribution of metals in the Galaxy provides important information about galaxy formation and evolution. H II regions are the most luminous objects in the Milky Way at mid-infrared to radio wavelengths and can be seen across the entire Galactic disk. We used the National Radio Astronomy Observatory (NRAO) Green Bank Telescope to measure radio recombination line and continuum emission in 81 Galactic H II regions. We calculated LTE electron temperatures using these data. In thermal equilibrium metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. Our H II region distribution covers a large range of Galactocentric radius (5-22 kpc) and samples the Galactic azimuth range 330{sup 0}-60{sup 0}. Using our highest quality data (72 objects) we derived an O/H Galactocentric radial gradient of -0.0383 {+-} 0.0074 dex kpc{sup -1}. Combining these data with a similar survey made with the NRAO 140 Foot telescope we get a radial gradient of -0.0446 {+-} 0.0049 dex kpc{sup -1} for this larger sample of 133 nebulae. The data are well fit by a linear model and no discontinuities are detected. Dividing our sample into three Galactic azimuth regions produced significantly different radial gradients that range from -0.03 to -0.07 dex kpc{sup -1}. These inhomogeneities suggest that metals are not well mixed at a given radius. We stress the importance of homogeneous samples to reduce the confusion of comparing data sets with different systematics. Galactic chemical evolution models typically derive chemical evolution along only the radial dimension with time. Future models should consider azimuthal evolution as well.

• OSTI ID: 21582956
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 738; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
DISTRIBUTION
ELECTRON TEMPERATURE
ELEMENT ABUNDANCE
ELEMENTS
EMISSION
EQUILIBRIUM
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
LTE
METALS
MILKY WAY
THERMAL EQUILIBRIUM