Astron. Astrophys. 333, L75-L78 (1998)

Letter to the Editor

Faint [O iv] emission from starburst galaxies ^*

D. Lutz , D. Kunze , H.W.W. Spoon and M.D. Thornley

Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany

Received 11 March 1998 / Accepted 27 March 1998

Abstract

We report the detection of faint emission in the high-excitation [O iv] 25.90 µm line in a number of starburst galaxies, from observations obtained with the Short Wavelength Spectrometer (SWS) on board ISO. Further observations of M 82 spatially resolve the [O iv] emitting region. Detection of this line in starbursts is surprising since it is not produced in measurable quantities in H ii regions around hot main-sequence stars, the dominant energy source of starburst galaxies. We discuss various models for the formation of this line. [O iv] that is spatially resolved by ISO cannot originate in a weak AGN and must be due to very hot stars or ionizing shocks related to the starburst activity. For low-excitation starbursts like M 82 , shocks are the most plausible source of [O iv] emission.

Key words: galaxies: ISM galaxies: starburst infrared: galaxies

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States and with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.

Send offprint requests to: D. Lutz (e-mail: lutz@mpe.mpg.de)

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Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. Results
  • 3.1. Spatially resolved [O iv] emission in M 82
• 4. Discussion
  • 4.1. Weak AGNs
  • 4.2. Super-hot stars
  • 4.3. Planetary nebulae
  • 4.4. Ionizing shocks
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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