Astron. Astrophys. 361, 888-894 (2000)

Radio jet-blown neutral hydrogen supershells in spiral galaxies?

Gopal-Krishna ¹ and Judith A. Irwin <sup>2

1</sup> National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Pune - 411007, India (krishna@ncra.tifr.res.in)
² Department of Physics, Queen's University, Kingston, K7L 3N6, Canada (irwin@astro.queensu.ca)

Received 21 April 2000 / Accepted 8 August 2000

Abstract

Taking a clue from the pair of HI supershells found in the Scd galaxy NGC 3556 (M 108), we propose a new mechanism for the origin of HI supershells in gas-rich massive galaxies. In this scenario, the two supershells were inflated out of the neutral hydrogen disk due to the localised flaring of a pair of radio lobes formed by the jets ejected from the nucleus during an active phase about years ago, but have faded away by now. It is shown that the salient features of this supershell pair, such as their symmetrical locations about the galactic centre, the anomalously large energy requirements, the large galacto-centric distances, as well as the Z-symmetric hemispherical shapes, find a more natural explanation in terms of this scenario, as compared to the standard models which postulate either a massive starburst, or the infall of external gas clouds. Other possible implications of this hypothesis are briefly discussed.

Key words: galaxies: general galaxies: ISM galaxies: jets galaxies: kinematics and dynamics radio continuum: galaxies radio lines: ISM

Send offprint requests to: J.A. Irwin

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Contents

• 1. Introduction
• 2. The case for a radio jet origin for HI supershells
  • 2.1. Radio jets and AGN in spiral galaxies
  • 2.2. Jet inflated bubbles in the lobes of radio galaxies
  • 2.3. Candidate galaxies
    • 2.3.1. NGC 3556
    • 2.3.2. Other examples
• 3. A new model for the formation of HI supershells
  • 3.1. Need for a new mechanism
  • 3.2. Outline of the model
• 4. Summary and possible implications
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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