We present and discuss European VLBI Network UHF band spectral line observations, made to localise the redshifted 21cm HI absorption known to occur in the subgalactic sized compact steep spectrum galaxies 3C 49 and 3C 268.3. We have detected HI absorption towards the western radio lobe of 3C 49 and the northern lobe of 3C 268.3. However, we cannot rule out the presence of similar amounts of HI towards the opposite and much fainter lobes. The radio lobes with detected HI absorption (1) are brighter and closer to the core than the opposite lobes; (2) are depolarized; and (3) are associated with optical emission line gas. The association between the HI absorption and the emission line gas, supports the hypothesis that the HI absorption is produced in the atomic cores of the emission line clouds. Our results are consistent with a picture in which compact steep spectrum sources interact with clouds of dense gas as they propagate through their host galaxy. We suggest that the asymmetries in the radio and optical emission can be due to interaction of a two sided radio source with an asymmetric distribution of dense clouds in their environment.

Publication Date



This is the pre-print of an article published by EDP Sciences. The final, published version is available here: https://doi.org/10.1051/0004-6361:20053856

Reproduced with permission from Astronomy & Astrophysics, © 2006 ESO

Also archived in: arXiv: astro-ph/0510563 v1 19 Oct 2005

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of NASA’s Astrophysics Data System. The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils.

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Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus