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Issue A&A
Volume 373, Number 2, July II 2001
Page(s) 485 - 493
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010614



A&A 373, 485-493 (2001)
DOI: 10.1051/0004-6361:20010614

A search for intergalactic H I gas in the NGC 1808 group of galaxies

M. Dahlem1, M. Ehle2, 3 and S. D. Ryder4

1  Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
2  XMM-Newton Science Operations Centre, Apartado 50727, 28080 Madrid, Spain
3  Astrophysics Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
4  Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia

(Received 21 March 2001 / Accepted 27 April 2001)

Abstract
A mosaic of six H I line observations with the Australia Telescope Compact Array is used to search for intergalactic gas in the NGC 1808 group of galaxies. Within the field of view of about $1\fdg4\times1\fdg2$ no emission from intergalactic H I gas is detected, either in the form of tidal plumes or tails, intergalactic H I clouds, or as gas associated with tidal dwarf galaxies, with a 5 $\sigma$ limiting sensitivity of about $3\times 10^{18}$ cm-2 (or $1.4\times 10^7 M_\odot$ at a distance of 10.9 Mpc, for the given beam size of $127\farcs9\times77\farcs3$). The H I data of NGC 1792 and NGC 1808, with a velocity resolution of 6.6 km s-1, confirm the results of earlier VLA observations. Simultaneous wide-band 1.34 GHz continuum observations also corroborate the results of earlier studies. However, the continuum flux of NGC 1808 measured by us is almost 20% higher than reported previously. No radio continuum emission was detected from the type Ia supernova SN1993af in the north-eastern spiral arm of NGC 1808. A comparison of NGC 1792 and NGC 1808 shows that it is not primarily the total energy input that makes the big difference between the starburst-related outflow in NGC 1808 and the absence of such extraplanar features in NGC 1792, but the area over which the energy released by stellar winds and supernovae is injected into the ISM.


Key words: galaxies: individual: NGC 1792, NGC 1808 -- galaxies: general -- galaxies: ISM -- galaxies: interactions -- intergalactic medium

Offprint request: M. Dahlem, mdahlem@eso.org

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© ESO 2001

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