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Formation of Narrow Hell λ4686 Emission in HII Galaxies: Link with X-Ray Emission

Published online by Cambridge University Press:  10 November 2010

G. Tenorio-Tagle
Affiliation:
Instituto de Astrofísica de Canarias, Tenerife
C. Motch
Affiliation:
Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France; Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany
M. W. Pakull
Affiliation:
Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France
W. Pietsch
Affiliation:
Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany
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Summary

ROSAT and optical observations of NGC 4861 and NGC 5408, two HII galaxies exhibiting both narrow Hell λ4686 emission line and luminous soft X-ray emission reveal that X-ray and line emitting regions are spatially distinct. This demonstrates that the X-ray ionization mechanism which accounts for the HeIII regions around luminous X-ray sources in the LMC is not at work on a large scale in these two HII galaxies. We Briefly review alternative explanations for the formation of the narrow Hell λ4686 line. The X-ray spectrum of NGC 4861 is soft and probably not dominated by young accreting neutron stars. Accreting black holes of stellar masses, hot gas and SNRs may account for the integrated X-ray energy distribution.

Introduction

Although the strength of most emission lines observed in HII galaxies are in excellent agreement with those expected from the ionization by clusters of massive O stars, the presence of narrow, presumably nebular HeII λ4684 emission with an intensity of ≈ 1 % of that of Hβ in some HII galaxies is not yet well understood (see e.g. Campbell 1988; Conti, 1991). There are strong indications that the gas is photoionized and that shock excitation, if present at all, is not responsible for the emission of this high-ionization line. The origin of the luminous He+ Lyman continuum is currently a matter of debate since normal O stars have generally been thought to emit only negligible amounts of He+ ionizing photons.

Type
Chapter
Information
Violent Star Formation
From 30 Doradus to QSOs
, pp. 208 - 213
Publisher: Cambridge University Press
Print publication year: 1994

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  • Formation of Narrow Hell λ4686 Emission in HII Galaxies: Link with X-Ray Emission
    • By C. Motch, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France; Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany, M. W. Pakull, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France, W. Pietsch, Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany
  • G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
  • Book: Violent Star Formation
  • Online publication: 10 November 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600159.036
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  • Formation of Narrow Hell λ4686 Emission in HII Galaxies: Link with X-Ray Emission
    • By C. Motch, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France; Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany, M. W. Pakull, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France, W. Pietsch, Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany
  • G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
  • Book: Violent Star Formation
  • Online publication: 10 November 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600159.036
Available formats
×

Send book to Google Drive

To send content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about sending content to Google Drive.

  • Formation of Narrow Hell λ4686 Emission in HII Galaxies: Link with X-Ray Emission
    • By C. Motch, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France; Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany, M. W. Pakull, Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France, W. Pietsch, Max-Planck-Institut fũr Extraterrestrische Physik, W-85470, Garching, Germany
  • G. Tenorio-Tagle, Instituto de Astrofísica de Canarias, Tenerife
  • Book: Violent Star Formation
  • Online publication: 10 November 2010
  • Chapter DOI: https://doi.org/10.1017/CBO9780511600159.036
Available formats
×