A&A 395, L13-L16 (2002)
DOI: 10.1051/0004-6361:20021408

Letter

Evolution of clouds in radio galaxy cocoons

G. Mellema, J. D. Kurk and H. J. A. Röttgering

Sterrewacht Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands

(Received 31 July 2002 / Accepted 6 September 2002)

Abstract
This letter presents a numerical study of the evolution of an emission line cloud of initial density 10 cm ^-3, temperature  10⁴ K, and size 200 pc, being overtaken by a strong shock wave. Whereas previous simple models proposed that such a cloud would either be completely destroyed, or simply shrink in size, our results show a different and more complex behaviour: due to rapid cooling, the cloud breaks up into many small and dense fragments, which can survive for a long time. We show that such rapid cooling behaviour is expected for a wide range of cloud and shock properties. This process applies to the evolution of emission line clouds being overtaken by the cocoon of a radio jet. The resulting small clouds would be Jeans unstable, and form stars. Our results thus give theoretical credibility to the process of jet induced star formation, one of the explanations for the alignment of the optical/UV and radio axis observed in high redshift radio galaxies.

Key words: galaxies: jets -- galaxies: high redshift -- galaxies: active -- galaxies: evolution -- cosmology: early Universe

Offprint request: G. Mellema, mellema@strw.leidenuniv.nl

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© ESO 2002

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