4.7 Article

Strongly star forming galaxies in the local Universe with nebular He II λ4686 emission

期刊

出版社

OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2012.20439.x

关键词

stars: Wolf-Rayet; galaxies: evolution; galaxies: star formation; galaxies: stellar content

资金

  1. Alfred P. Sloan Foundation
  2. National Science Foundation
  3. US Department of Energy
  4. National Aeronautics and Space Administration
  5. Japanese Monbukagakusho
  6. Max Planck Society
  7. Higher Education Funding Council for England
  8. American Museum of Natural History
  9. Astrophysical Institute Potsdam
  10. University of Basel
  11. University of Cambridge
  12. Case Western Reserve University
  13. University of Chicago
  14. Drexel University, Fermilab
  15. Institute for Advanced Study
  16. Japan Participation Group
  17. Johns Hopkins University
  18. Joint Institute for Nuclear Astrophysics
  19. Kavli Institute for Particle Astrophysics and Cosmology
  20. Korean Scientist Group
  21. Chinese Academy of Sciences (LAMOST)
  22. Los Alamos National Laboratory
  23. Max-Planck-Institute for Astronomy (MPIA)
  24. Max-Planck-Institute for Astrophysics (MPA)
  25. New Mexico State University
  26. Ohio State University
  27. University of Pittsburgh
  28. University of Portsmouth
  29. Princeton University
  30. United States Naval Observatory
  31. University of Washington
  32. Particle Physics and Astronomy Research Council (PPARC)
  33. Joint Astronomy Centre Hawaii

向作者/读者索取更多资源

We present a sample of 2865 emission-line galaxies with strong nebular He II lambda 4686 emissions in the Sloan Digital Sky Survey Data Release 7 and use this sample to investigate the origin of this line in star-forming galaxies. We show that star-forming galaxies and galaxies dominated by an active galactic nucleus form clearly separated branches in the He II lambda 4686/H beta versus [N-II]lambda 6584/H alpha diagnostic diagram and derive an empirical classification scheme which separates the two classes. We also present an analysis of the physical properties of 189 star-forming galaxies with strong He II lambda 4686 emissions. These star-forming galaxies provide constraints on the hard ionizing continuum of massive stars. To make a quantitative comparison with observation, we use photoionization models and examine how different stellar population models affect the predicted He II lambda 4686 emission. We confirm previous findings that the models can predict He II lambda 4686 emission only for instantaneous bursts of 20 per cent solar metallicity or higher, and only for ages of similar to 4-5 Myr, the period when the extreme-ultraviolet continuum is dominated by emission from Wolf-Rayet stars. We find, however, that 83 of the star-forming galaxies (40 per cent) in our sample do not have Wolf-Rayet features in their spectra despite showing strong nebular He II lambda 4686 emission. We discuss possible reasons for this and possible mechanisms for the He II lambda 4686 emission in these galaxies.

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