Small and young radio sources
  It is currently accepted that compact and bright radio sources characterized
by a convex spectrum peaking at frequencies ranging from 100 MHz to a few GHz
are young objects. In this scenario, high frequency peaker (HFP) radio sources,
with a turnover frequency higher than 5 GHz are good candidates to be extremely
young radio sources with ages of up to a few thousand years. The knowledge of
the conditions in young radio source is fundamental in order to draw reliable
evolution models able to describe the entire life-cycle of the radio emission.
Given the high spatial resolution and the large frequency range spanned, VLBI
observations provide a unique opportunity to constrain the physical conditions
in young radio sources, and to investigate the role played by the environment
on the source growth.
