OH masers in the Milky Way and Local Group galaxies in the SKA era
  The intense line emission of OH masers is a perfect tracer of regions where
new stars are born aswell as of evolved stars, shedding large amounts of
processed matter into the interstellar medium. From SKA deep surveys at 18 cm,
where the maser lines from the ground-state of the OH molecule arise, we
predict the discovery of more than 20000 sources of stellar and interstellar
origin throughout the Galaxy. The study of this maser emission has many
applications, including the determination of magnetic field strengths from
polarisation measurements, studies of stellar kinematics using the precisely
determined radial velocities, and distance determinations from VLBI astrometry.
A new opportunity to study shocked gas in different galactic environments is
expected to arise with the detection of lower luminosity masers. For the first
time, larger numbers of OH masers will be detected in Local Group galaxies. New
insights are expected in structure formation in galaxies by comparing maser
populations in galaxies of different metallicity, as both their properties as
well as their numbers depend on it. With the full capabilities of SKA, further
maser transitions such as from excited OH and from methanol will be accessible,
providing new tools to study the evolution of star-forming regions in
particular.
