ALMA 13CO(J = 1 − 0) observations of NGC 604 in M33: Physical properties of molecular clouds

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 13CO(J = 1 − 0) line and 104 GHz continuum emission from NGC 604, a giant H ii region (GHR) in the nearby spiral galaxy M33. Our high spatial resolution images (3.2″ × 2.4″, corresponding to 13 × 10 pc physical scale) allow us to detect fifteen molecular clouds. We find spatial offsets between the 13CO and 104 GHz continuum emission and also detect continuum emission near the centre of the GHR. The identified molecular clouds have sizes ranging from 5-21 pc, linewidths of 0.3-3.0 km s−1 and luminosity-derived masses of (0.4–80.5) × 103 M⊙. These molecular clouds are in near virial equilibrium, with a Spearman correlation coefficient of 0.98. The linewidth-size relationship for these clouds is offset from the corresponding relations for the Milky Way and for NGC 300, although this may be an artefact of the dendrogram process.