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Astron. Astrophys. 356, L1-L4 (2000)

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Letter to the Editor

First detection of molecular gas in the shells of CenA *

V. Charmandaris 1,2, F. Combes 1 and J.M. van der Hulst 3

1 Observatoire de Paris, DEMIRM, 61 Avenue de l'Observatoire, 75014 Paris, France
2 Cornell University, Astronomy Department, Ithaca, NY 14853-6801, USA
3 University of Groningen, Kapteyn Institute, Postbus 800, 9700 AV, Groningen, The Netherlands

Received 14 January 2000 / Accepted 17 February 2000


Shells are faint arc-like stellar structures, which have been observed around early type galaxies and are thought to be the result of an interaction. HI gas has recently been detected in shells, a surprising result in view of the theoretical predictions that most of the gas should decouple from stars and fall into the nucleus in such interactions. Here we report the first detection of molecular gas (CO) in shells, found 15 kpc away from the center of NGC 5128 (CenA), a giant elliptical galaxy that harbors an active nucleus (AGN). The ratio between CO and HI emission in the shells is the same as that found in the central regions, which is unexpected given the metallicity gradient usually observed in galaxies. We propose that the dynamics of the gas can be understood within the standard picture of shell formation if one takes into account that the interstellar medium is clumpy and hence not highly dissipative. The observed metal enrichment could be due to star formation induced by the AGN jet in the shells. Furthermore our observations provide evidence that molecular gas in mergers may be spread out far from the nuclear regions.

Key words: galaxies: individual: Centaurus A – galaxies: interactions – galaxies: ISM – galaxies: jets – radio lines: galaxies

* Based on observations made with the Swedish-ESO Submillimeter Telescope (SEST) at La Silla, Chile

Send offprint requests to: V. Charmandaris (vassilis@astro.cornell.edu)

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© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000