Title:MegaMorph: advanced galaxy decomposition for large multi-wavelength 
surveys

Abstract:
Most galaxies can be considered to be, at least approximately, two-component 
stellar systems, containing both a spheroid and disk.  These components have 
distinct formation histories, and thus separating their properties provides a 
more complete picture of galaxy evolution.  Unfortunately, performing this 
decomposition presents significant challenges, particularly in large surveys, 
where an automated method is essential.

Established decomposition solutions use just one image, at a single wavelength, 
to determine a galaxy''s structural parameters; occasionally making use of a 
secondary image to measure colour information.  However, modern surveys 
routinely produce imaging in many near-UV to near-IR bands.  Utilising all this 
available data increases the signal-to-noise available to constrain the 
structural model.  More importantly, the components typically possess different 
colours, which allows them to be much more robustly separated.

Our MegaMorph project has adapted tried-and-tested software (GALFIT and 
GALAPAGOS) to fit a consistent, wavelength-dependent model to imaging in an 
arbitrary set of photometric bands.  We have tested our technique on both real 
and simulated data in a variety of observational regimes.  I will describe our 
approach, and demonstrate that it enables more accurate, robust and physically 
meaningful multi-wavelength measurements of galaxy structural components.  This 
paves the way for reliably studying the physical properties (stellar mass and 
age) of spheroids and disks for very large samples.