Biases in physical parameter estimates through differential lensing
  magnification
  We study the lensing magnification effect on background galaxies.
Differential magnification due to different magnifications of different source
regions of a galaxy will change the lensed composite spectra. The derived
properties of the background galaxies are therefore biased. For simplicity, we
model galaxies as a superposition of an axis-symmetric bulge and a face-on disk
in order to study the differential magnification effect on the composite
spectra. We find that some properties derived from the spectra (e.g., velocity
dispersion, star formation rate and metallicity) are modified. Depending on the
relative positions of the source and the lens, the inferred results can be
either over- or under-estimates of the true values. In general, for an extended
source at strong lensing regions with high magnifications, the inferred
physical parameters (e.g. metallicity) can be strongly biased. Therefore
detailed lens modelling is necessary to obtain the true properties of the
lensed galaxies.
