HI absorption in 3C 49 and 3C 268.3 - Probing the environment of compact steep spectrum and GHz peaked spectrum sources

Aims. Localize and study the redshifted 21 cm H I absorption known to occur in the subgalactic sized compact steep spectrum galaxies 3C 49 and 3C 268.3.

Methods. We carried out European VLBI Network UHF hand spectral line observations.

Results. We have detected H I 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 H I towards the opposite and much fainter lobes. The radio lobes with detected H I 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 H I absorption and the emission line gas, Supports the hypothesis that the H I 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.