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We have recently conducted a sensitive survey of a square degree region of the outer Galaxy. It is the first survey to be sensitive to clouds which are small and/or have low surface brightness. Two populations of molecular clouds have been identified, arm and interarm. The arm population (centered at 12.5 kpc) consists of clouds with masses from ${\rm 10^{5} M_{\odot}}$ (typical GMC's) to ${\rm 10^3 M_{\odot}}$. Most of the mass in this part of the molecular arm is contained in the GMC's. The interarm population is dominated by smaller clouds which are distributed throughout the survey region. The low mass end of the cloud size distribution for the entire survey region will be compared with existing theory to see if the power law behavior of the size distribution holds for small clouds. The question of whether small, cold clouds constitute a significant component of the total molecular mass of the outer Galaxy will be addressed. In addition, detailed comparisons of how the cloud size distributions differ for the two populations will be presented.
Our survey is a one beamwidth (60") sampled survey of a square degree region of the outer Galaxy (centered on $l = 76.37^{\circ}$, $b = 1.45^{\circ}$) in ${\rm {}^{12}CO \: J = 1 \rightarrow 0}$, using the ${\rm NRAO^{\ast}}$ 12m telescope. The survey covers R between 9 and 16 kpc. The ${\rm 1 \sigma}$ rms noise level for each position is ${\rm T^{\ast}_{\tiny R} = .1 \: K}$. Unlike previous surveys, which were either undersampled or of low resolution, our survey is sensitive to small (${\rm \sim 5 \: pc}$) and/or faint line (${\rm T_{peak} = .4 \: K}$) clouds.
\noindent S. Carey was aided by the travel support program of the Astronomical Society of New York and a Grant-in-Aid of Research from the National Academy of Sciences, through Sigma Xi, The Scientific Research Society.
\noindent ${\rm {}^{\ast}}$ The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the NSF.
