The Herschel Exploitation of Local Galaxy Andromeda (HELGA). VI. The
  distribution and properties of molecular cloud associations in M31
  In this paper we present a catalogue of Giant Molecular Clouds (GMCs) in the
Andromeda (M31) galaxy extracted from the Hershel Exploitation of Local Galaxy
Andromeda (HELGA) dataset. GMCs are identified from the Herschel maps using a
hierarchical source extraction algorithm. We present the results of this new
catalogue and characterise the spatial distribution and spectral energy
properties of its clouds based on the radial dust/gas properties found by Smith
et al (2012). 236 GMCs in the mass range 10^4-10^7 M_sol are identified, their
cumulative mass distribution is found to be proportional to M^-1.45 in
agreement with earlier studies. The GMCs appear to follow the same cloud mass
to L_CO correlation observed in the Milky Way. However, comparison between this
catalogue and interferometry studies also shows that the GMCs are substructured
below the Herschel resolution limit suggesting that we are observing
associations of GMCs. Following Gordon et al. (2006), we study the spatial
structure of M31 by splitting the observed structure into a set of spiral arms
and offset rings. We fit radii of 10.5 and 15.5 kpc to the two most prominent
rings. We then fit a logarithmic spiral with a pitch angle of 8.9 deg to the
GMCs not associated with either ring. Lastly, we comment upon the effects of
deprojection on our results and investigate the effect different models for
M31's inclination will have upon the projection of an unperturbed spiral arm
system.
