Emission Lines as a Tool in Search for Supermassive Black Hole Binaries
  and Recoiling Black Holes
  Detection of electromagnetic (EM) counterparts of pre-coalescence binaries
has very important implications for our understanding of the evolution of these
systems as well as the associated accretion physics. In addition, a combination
of EM and gravitational wave signatures observed from coalescing supermassive
black hole binaries (SBHBs) would provide independent measurements of redshift
and luminosity distance, thus allowing for high precision cosmological
measurements. However, a statistically significant sample of these objects is
yet to be attained and finding them observationally has proven to be a
difficult task. Here we discuss existing observational evidence and how further
advancements in the theoretical understanding of observational signatures of
SBHBs before and after the coalescence can help in future searches.
