The extended disc and halo of the Andromeda galaxy observed with
  Spitzer-IRAC
  We present the first results from an extended survey of the Andromeda galaxy
(M31) using 41.1 h of observations by Spitzer-IRAC at 3.6 and 4.5$\,\mu$m. This
survey extends previous observations to the outer disc and halo, covering total
lengths of 4$.\!\!^\circ$4 and 6$.\!\!^\circ$6 along the minor and major axes,
respectively. We have produced surface brightness profiles by combining the
integrated light from background-corrected maps with stellar counts from a new
catalogue of point sources. Using auxiliary catalogues we have carried out a
statistical analysis in colour-magnitude space to discriminate M31 objects from
foreground Milky Way stars and background galaxies. The catalogue includes
426,529 sources, of which 66 per cent have been assigned probability values to
identify M31 objects with magnitude depths of [3.6]$\,=\,$19.0$\,\pm\,$0.2,
[4.5]$\,=\,$18.7$\,\pm\,$0.2. We discuss applications of our data for
constraining the stellar mass and characterising point sources in the outer
radii.
