  Angle-resolved photoemission spectroscopy (ARPES) is used to study the band
dispersion and the quasiparticle scattering rates in two ferropnictides
systems. Our ARPES results show linear-in-energy dependent scattering rates
which are constant in a wide range of control parameter and which depend on the
orbital character of the bands. We demonstrate that the linear energy
dependence gives rise to weakly dispersing band with a strong mass enhancement
when the band maximum crosses the chemical potential. In the superconducting
phase the related small effective Fermi energy favors a
Bardeen-Cooper-Schrieffer (BCS)\,\cite{Bardeen1957}-Bose-Einstein
(BE)\,\cite{Bose1924} crossover state.
