  Any expanding homogeneous Ricci soliton (in particular any homogeneous
Einstein manifold of negative scalar curvature) can be obtained, up to
isometry, from a Lie subgroup of a nilpotent Iwasawa group $N$ whose induced
metric is a Ricci soliton. By nilpotent Iwasawa group we mean the nilpotent Lie
group $N$ of the Iwasawa decomposition associated with a symmetric space of
non-compact type. Motivated by this fact, in this paper we classify codimension
one Lie subgroups of any nilpotent Iwasawa group $N$ whose induced metric is a
Ricci soliton.
