First Resolved Dust Continuum Measurements of Individual Giant Molecular
  Clouds in the Andromeda Galaxy
  In our local Galactic neighborhood, molecular clouds are best studied using a
combination of dust measurements, to determine robust masses, sizes and
internal structures of the clouds, and molecular-line observations to determine
cloud kinematics and chemistry. We present here the first results of a program
designed to extend such studies to nearby galaxies beyond the Magellanic
Clouds. Utilizing the wideband upgrade of the Submillimeter Array (SMA) at 230
GHz we have obtained the first continuum detections of the thermal dust
emission on sub-GMC scales ($\sim$ 15 pc) within the Andromeda galaxy (M31).
These include the first resolved continuum detections of dust emission from
individual GMCs beyond the Magellanic Clouds. Utilizing a powerful capability
of the SMA, we simultaneously recorded CO(2-1) emission with identical
$(u,\,v)$ coverage, astrometry and calibration, enabling the first measurements
of the CO conversion factor, $\alpha_{\rm\,CO(2-1)}$, toward individual GMCs
across an external galaxy. Our direct measurement yields an average
CO--to--dust mass conversion factor of $\alpha^\prime_{\rm CO-dust} =
0.042\pm0.018$ $M_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the $J= 2-1$
transition. This value does not appear to vary with galactocentric radius.
Assuming a constant gas-to-dust ratio of 136, the resulting $\alpha_{\rm CO}$
$=$ 5.7 $\pm$ 2.4 $M_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the 2-1
transition is in excellent agreement with that of Milky Way GMCs, given the
uncertainties. Finally, using the same analysis techniques, we compare our
results with observations of the local Orion molecular clouds, placed at the
distance of M31 and simulated to appear as they would if observed by the SMA.
