MegaMorph - multi-wavelength measurement of galaxy structure: complete
  S\'ersic profile information from modern surveys
  In this paper, we demonstrate a new method for fitting galaxy profiles which
makes use of the full multi-wavelength data provided by modern large
optical-near-infrared imaging surveys. We present a new version of GALAPAGOS,
which utilises a recently-developed multi-wavelength version of GALFIT, and
enables the automated measurement of wavelength dependent S\'ersic profile
parameters for very large samples of galaxies. Our new technique is extensively
tested to assess the reliability of both pieces of software, GALFIT and
GALAPAGOS on both real ugrizY JHK imaging data from the GAMA survey and
simulated data made to the same specifications. We find that fitting galaxy
light profiles with multi-wavelength data increases the stability and accuracy
of the measured parameters, and hence produces more complete and meaningful
multi-wavelength photometry than has been available previously. The improvement
is particularly significant for magnitudes in low S/N bands and for structural
parameters like half-light radius re and S\'ersic index n for which a prior is
used by constraining these parameters to a polynomial as a function of
wavelength. This allows the fitting routines to push the magnitude of galaxies
for which sensible values can be derived to fainter limits. The technique
utilises a smooth transition of galaxy parameters with wavelength, creating
more physically meaningful transitions than single-band fitting and allows
accurate interpolation between passbands, perfect for derivation of rest-frame
values.
