Microlensing of the broad line region in 17 lensed quasars
  When an image of a strongly lensed quasar is microlensed, the different
components of its spectrum are expected to be differentially magnified owing to
the different sizes of the corresponding emitting region. Chromatic changes are
expected to be observed in the continuum while the emission lines should be
deformed as a function of the size, geometry and kinematics of the regions from
which they originate. Microlensing of the emission lines has been reported only
in a handful of systems so far. In this paper we search for microlensing
deformations of the optical spectra of pairs of images in 17 lensed quasars.
This sample is composed of 13 pairs of previously unpublished spectra and four
pairs of spectra from literature. Our analysis is based on a spectral
decomposition technique which allows us to isolate the microlensed fraction of
the flux independently of a detailed modeling of the quasar emission lines.
Using this technique, we detect microlensing of the continuum in 85% of the
systems. Among them, 80% show microlensing of the broad emission lines.
Focusing on the most common lines in our spectra (CIII] and MgII) we detect
microlensing of either the blue or the red wing, or of both wings with the same
amplitude. This observation implies that the broad line region is not in
general spherically symmetric. In addition, the frequent detection of
microlensing of the blue and red wings independently but not simultaneously
with a different amplitude, does not support existing microlensing simulations
of a biconical outflow. Our analysis also provides the intrinsic flux ratio
between the lensed images and the magnitude of the microlensing affecting the
continuum. These two quantities are particularly relevant for the determination
of the fraction of matter in clumpy form in galaxies and for the detection of
dark matter substructures via the identification of flux ratio anomalies.
