Journal Article

A kinematic study of the neutral and ionized gas in the irregular dwarf galaxies IC 4662 and NGC 5408*

Janine van Eymeren, Bärbel S. Koribalski, Ángel R. López-Sánchez, Ralf-Jürgen Dettmar and Dominik J. Bomans

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 1, pages 113-132
Published in print September 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16923.x
A kinematic study of the neutral and ionized gas in the irregular dwarf galaxies IC 4662 and NGC 5408*

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The feedback between massive stars and the interstellar medium is one of the most important processes in the evolution of dwarf galaxies. This interaction results in numerous neutral and ionized gas structures that have been found both in the disc and in the halo of these galaxies. However, their origin and fate are still poorly understood.

We here present new H i and optical data of two Magellanic irregular dwarf galaxies in the Local Volume: IC 4662 and NGC 5408. The H i line data were obtained with the Australia Telescope Compact Array and are part of the ‘Local Volume H i Survey’. They are complemented by optical images and spectroscopic data obtained with the European Southern Observatory (ESO) New Technology Telescope and the ESO 3.6-m telescope. Our main aim is to study the kinematics of the neutral and ionized gas components in order to search for outflowing gas structures and to make predictions about their fate. Therefore, we perform a Gaussian decomposition of the H i and Hα line profiles.

We find the H i gas envelopes of IC 4662 and NGC 5408 to extend well beyond the optical discs, with H i to optical diameter ratios of above 4. The optical disc is embedded into the central H i maximum in both galaxies. However, higher resolution H i maps show that the H i intensity peaks are typically offset from the prominent H ii regions.

While NGC 5408 shows a fairly regular H i velocity field, which allows us to derive a rotation curve, IC 4662 reveals a rather twisted H i velocity field, possibly caused by a recent merger event. We detect outflows with velocities between 20 and 60 km s−1 in our Hα spectra of both galaxies, sometimes with H i counterparts of similar velocity. We suggest the existence of expanding superbubbles, especially in NGC 5408. This is also supported by the detection of full width at half-maxima as high as 70 km s−1 in Hα, which cannot be explained by thermal broadening alone. In the case of NGC 5408, we compare our results with the escape velocity of the galaxy, which shows that the measured expansion velocities are in all cases too low to allow the gas to escape from the gravitational potential of NGC 5408. This result is consistent with studies of other dwarf galaxies.

Keywords: galaxies: individual: IC 4662; galaxies: individual: NGC 5408; galaxies: ISM; galaxies: kinematics and dynamics; galaxies: structure

Journal Article.  12630 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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