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Erik Rosolowsky edited section_Description_of_the_data__.tex
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\section{Description of the data}
This project uses observations made by ALMA under project 2012.1.00762.S proposed by Hirota et al. We used the Quality Assurance, step 2 data (QA2) downloaded from the Japanese Virtual Observatory site, which images the CO(1-0) line at $1.34\times 0.83$ arcsec resolution, corresponding to $29\times 18$ pc at the 4.5 Mpc distance of M83 \citep{Thim_2003}. The imaged data cube has a velocity resolution of 2.57 km~s$^{-1}$. With a median brightness sensitivity of $\sigma=0.89$~K per beam, the data set are ideally suited for the identification and decomposition of GMCs \citep{Rosolowsky_2006}. Through this analysis, we adopt a CO-to-H$_2$ conversion factor of X$_{\mathrm{CO}} = 2\times 10^{20}$~(K~km~s$^{-1}$)$^{-1}$~cm$^{-2}$ \cite{Bolatto_2013}. With this conversion factor, the data cube has a $1\sigma$ mass surface density sensitivity of 9.9 $M_{\odot}~\mathrm{pc}^{-2}$ and a per-beam mass sensitivity of $6\times 10^3~M_{\odot}$.
Since the Quality Assurance data delivered as part of the project do not include total power or short spacing data, the resulting image is affected by some negative artifacts from when the cleaning process applied to the interferometer maps. These artifacts are most noticeable toward the bright emission in the nucleus of the galaxy. These artifacts are driven by missing flux from large-scale, diffuse emission components \citep[e.g.,][]{Pety_2013} and sidelobes around bright sources. The data show no evidence for bad calibration and, apart from the effects of spatial filtering, the data are of high quality (Figure \ref{fig:tmax}). The data are nonetheless well-suited for the task at hand, namely identifying the GMCs in the galaxy as bright compact features in the CO emission and then characterizing their properties.
