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Erik Rosolowsky edited Correlations_of_these_macroscopic_properties__.tex
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Correlations of these macroscopic properties give clues to the nature of the molecular medium. We compare the properties of the molecular clouds to those seen in the Milky Way study of \citet[][;S87]{Solomon_1987} because that work measured GMC properties using similar techniques as we do here. In Figure \ref{larson_figure}, we correlate the GMC properties and compare the result to the trends seen in the S87 data. First, we see (panel a) that there is good agreement between the virial and luminous masses in these clouds, and this is seen throughout the system. We color each datum by the galactocentric radius to highlight the variation in cloud properties across the face of the disk. The most massive clouds are found in the center of the galaxy, but these extreme clouds still show good agreement between the two mass estimates. Both mass estimates will be subject to $\sim 0.3~\mathrm{ dex}$ uncertainties, but even in high quality data, there remains about 0.5 dex of scatter \cite{Heyer_2009}.
The radius-velocity dispersion plot (Figure \ref{larson_figure}b) shows the size-line width scalings in these clouds. The Milky Way relationship shows a good lower bound for the population, but there is significant scatter to higher line widths at a give radius. These offset clouds are found in the center of the galaxy, and are also associated with the higher mass clouds. Such objects are typically seen in molecule rich environments, where the surface densities of clouds increase significantly \citep{Oka_2001,Rosolowsky_2005,Heyer_2009,Leroy_2015}.
Such clouds are also seen as outliers in the mass-radius plot (Figure \ref{larson_figure}c). Clouds at $R_{\mathrm{gal}}>0.5\mbox{ kpc}$ have a median surface density of $\langle \Sigma \rangle = M_{\odot}\mbox{ pc}^{-2}$ but clouds inside this radius have a median surface density of $\langle \Sigma \rangle = 1100 M_{\odot}\mbox{ pc}^{-2}$.
The figure Even with these changes across the face of the galaxy, the clouds all appears to show gravitational binding energies comparable to their kinetic energies. Figure \ref{larson_figure}d shows the correlation between surface density and the turbulent line width on 1 pc scales $\sigma_0 = \sigma_v/R^{1/2}$ (the $y$-axis shows
the square of this quantity). \citet{Heyer_2009} noted that
these quantities correlate even in clouds which show line widths and surface densities that depart significantly from the
objects we identify can be associated with Milky Way
molecular clouds. They have comparable sizes and mass scales, and they show relations. This relationship is roughly equivalent to the
same underlying relationship plotted in Figure \ref{larson_figure}a.
\citet{Solomon_1987} examined GMCs in the Milky Way and described a few key relationships that characterize the properties of these clouds. We derived these properties for the M83 clouds to be confident From this analysis, we conclude that
they we are
GMCs.
The M83 observing GMCs
exhibit a similar relationship for velocity line width $\mathrm{\sigma}$ that show properties comparable to
radius $R$ as those found in the Milky
Way GMCs, which have a fit Way, though we see real variations across the face of
$\sigma=\left(\frac{\pi^{1/2}R}{3.4}\right)^{0.5}$ kms$^{-1}$ (\ref{fig:rdv}). This allows us to conclude the
galaxy. In particular clouds
are in virial equilibrium \cite{Solomon_1987}. The virial mass $M_\mathrm{vir}$ can then be calculated from the size and velocity dispersion, while the luminous mass $M_\mathrm{lum}$ can be calculated from located within 500 pc of the
luminosity galaxy center have significantly higher line widths and
X$_\mathrm{CO}$ \cite{Rosolowsky_2006}. These masses surface densities for
M83 conform to a
1:1 ratio as expected (\ref{fig:mlummvir}). Finally, given radius, but the
luminous mass to radius relationships are also consistent with previous findings, with \citet{Solomon_1987} finding a fit of $M=540R^2 (M_\odot)$ (\ref{fig:rm}). From this we can infer local increases in these quantities in the galaxy center balance such that the
observations in M83 are of GMCs. clouds retain a good balance between gravitational and kinetic energies.