First detection of molecular gas in the shells of CenA

Shells are faint are-like stellar structures, which have been observed arou nd early type galaxies and are thought to be the result of an interaction. PII gas has recently been detected in shells, a surprising result in view o f the theoretical predictions that most of the gas should decouple from sta rs 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 cent er of NGC 5128 (CenA), a giant elliptical galaxy that harbors an active nuc leus (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 metalli city gradient usually observed in galaxies. We propose that the dynamics of the gas can be understood within the standard picture of shell formation i f one takes into account that the interstellar medium is clumpy and hence n ot highly dissipative. The observed metal enrichment could be due to star f ormation 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.