The First Measured Electron Temperatures for Metal-rich H II Regions in M51

Details The First Measured Electron Temperatures for Metal-rich H II Regions in M51 The First Measured Electron Temperatures for Metal-rich H II Regions in M51

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...607l..21g&link_type=abstract

The Astrophysical Journal, Volume 607, Issue 1, pp. L21-L24.

Astronomy and Astrophysics

Astronomy

52

Galaxies: Abundances, Galaxies: Evolution, Galaxies: Individual: Ngc Number: Ngc 5194, Galaxies: Spiral

Scientific paper

We present the first direct measurements of electron temperatures in two low-excitation, and thus assumed very metal-rich, H II regions, in the spiral galaxy M51. We detect the [N II] λ5755 line in both H II regions and derive Te from the λ5755/λ6583 intensity ratio. We find values Te([N II])=6000 K for CCM 72 and 7400 K for CCM 10. Oxygen abundances based on these temperatures are approximately a factor of 3 smaller than those derived previously from photoionization models. The higher electron temperatures also lead to S/O abundance ratios that are consistent with the solar neighborhood ratio at all metallicities, rather than the declining S/O at high metallicities inferred from earlier studies. The results suggest that metallicities in the disks of spiral galaxies do not rise to values as high as 3 or 4 times the solar value, in contradiction with abundances inferred from model calibrations of O/H versus strong emission lines.
Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.

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