  We present WSRT observations of the neutral hydrogen in the nearby radio
galaxy B2 0648+27. In emission, we detect a very large amount of HI (M_HI = 1.1
x 10^10 M_sun) that is distributed in a very extended disk, or ring-like
structure, of about 160 kpc in size. We also detect HI absorption against the
central radio continuum component. The detection of the HI, its structure and
kinematics, give us key information for building a possible evolutionary
scenario. The characteristics of the detected HI are explained as the result of
a major merger event that is likely to have occurred <10^9 yr ago.
Interestinly, we find that, when observed in radio continuum at higher
resolution, this galaxy has a double lobed, steep spectrum structure of about 1
kpc in size. Thus, despite its low radio power, B2 0648+27 bears striking
similarities with Compact Symmetric Objects, i.e. objects believed to represent
the early phase of radio galaxies (< few thousand yrs old). B2~0648+27 is one
of the few nearby radio galaxies where extended neutral hydrogen has been
detected so far. This, and other recent results, appear however to indicate
that nearby radio galaxies are more often gas rich than commonly assumed. The
phenomena described are likely to be much more common at high redshift and
galaxies like B2 0648+27 may provide valuable information on the evolution of
high redshift radio sources.

Astrophysics