Quasars as tracers of cosmic flows
  Quasars, as the most luminous persistent sources in the Universe, have broad
applications for cosmological studies. In particular, they can be employed to
directly measure the expansion history of the Universe, similarly to SNe Ia.
The advantage of quasars is that they are numerous, cover a broad range of
redshifts, up to $z = 7$, and do not show significant evolution of metallicity
with redshift. The idea is based on the relation between the time delay of an
emission line and the continuum, and the absolute monochromatic luminosity of a
quasar. For intermediate redshift quasars, the suitable line is Mg II. Between
December 2012 and March 2014, we performed five spectroscopic observations of
the QSO CTS C30.10 ($z = 0.900$) using the South African Large Telesope (SALT),
supplemented with photometric monitoring, with the aim of determining the
variability of the line shape, changes in the total line intensity and in the
continuum. We show that the method is very promising.
