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Astron. Astrophys. 343, 705-712 (1999)


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Long slit spectroscopy of diffuse ionized gas in NGC 55 *

B. Otte 1,2 and R.-J. Dettmar 1

1 Astronomisches Institut, Ruhr-Universität Bochum, D-44780 Bochum, Germany
2 Department of Astronomy, University of Wisconsin, Madison, WI 53706, USA

Received 23 October 1998 / Accepted 4 January 1999

Abstract

Spectroscopic measurements of emission line ratios and velocities are presented for ionized gas across the central plane of NGC 55, a late-type galaxy in the Sculptor group. The low metallicity in NGC 55 leads to relatively low line ratios of [S II ]/H[FORMULA] and [N II ]/H[FORMULA] for H II regions as well as the diffuse ionized gas. These are the first spectroscopical measurements of line ratios in ionized gas exterior to the stellar disc of NGC 55. Analysis of the line ratios and the relative velocities of different features suggests that photoionization is a plausible explanation for the ionization of this diffuse gas. The observed shell structures and the corresponding velocities support the idea of diffuse gas being pushed into the halo by supernova explosions and stellar winds.

Key words: ISM: bubbles – ISM: general – ISM: H ii regions – galaxies: individual: NGC 55 – galaxies: ISM

* Based on observations obtained at ESO/La Silla

Correspondence to: otte@astro.wisc.edu

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999

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