  Recently, Jablonski proved that, to a large extent, a simply connected
solvable Lie group endowed with a left-invariant Ricci soliton metric can be
isometrically embedded into the solvable Iwasawa group of a non-compact
symmetric space. Motivated by this result, we classify codimension one
subgroups of the solvable Iwasawa groups of irreducible symmetric spaces of
non-compact type whose induced metrics are Ricci solitons. We also obtain the
classifications of codimension one Ricci soliton subgroups of Damek-Ricci
spaces and generalized Heisenberg groups.

Differential Geometry