The Panchromatic Hubble Andromeda Treasury V: Ages and Masses of the
  Year 1 Stellar Clusters
  We present ages and masses for 601 star clusters in M31 from the analysis of
the six filter integrated light measurements from near ultraviolet to near
infrared wavelengths, made as part of the Panchromatic Hubble Andromeda
Treasury (PHAT). We derive the ages and masses using a probabilistic technique,
which accounts for the effects of stochastic sampling of the stellar initial
mass function. Tests on synthetic data show that this method, in conjunction
with the exquisite sensitivity of the PHAT observations and their broad
wavelength baseline, provides robust age and mass recovery for clusters ranging
from $\sim 10^2 - 2 \times 10^6 M_\odot$. We find that the cluster age
distribution is consistent with being uniform over the past $100$ Myr, which
suggests a weak effect of cluster disruption within M31. The age distribution
of older ($>100$ Myr) clusters fall towards old ages, consistent with a
power-law decline of index $-1$, likely from a combination of fading and
disruption of the clusters. We find that the mass distribution of the whole
sample can be well-described by a single power-law with a spectral index of
$-1.9 \pm 0.1$ over the range of $10^3-3 \times 10^5 M_\odot$. However, if we
subdivide the sample by galactocentric radius, we find that the age
distributions remain unchanged. However, the mass spectral index varies
significantly, showing best fit values between $-2.2$ and $-1.8$, with the
shallower slope in the highest star formation intensity regions. We explore the
robustness of our study to potential systematics and conclude that the cluster
mass function may vary with respect to environment.
