Gathering dust: A galaxy-wide study of dust emission from cloud complexes in NGC 300

摘要

We used multi-band observations by the Herschel Space Observatory to studythe dust emission properties of the nearby spiral galaxy NGC 300. We compiled afirst catalogue of the population of giant dust clouds (GDCs) in NGC 300 andgive an estimate of the total dust mass of the galaxy. We carried out sourcedetection with the multiwavelength source extraction algorithm getsources andcalculated physical properties of the GDCs, including mass and temperature,from five-band Herschel PACS and SPIRE observations from 100-500 $\mu$m; thefinal size and mass estimates are based on the observations at 250 $\mu$m thathave an effective spatial resolution of $\sim$170 pc. We correlated our finalcatalogue of GDCs to pre-existing catalogues of HII regions to infer the numberof GDCs associated with high-mass star formation and determined the H$\alpha$emission of the GDCs. Our final catalogue of GDCs includes 146 sources, 90 ofwhich are associated with known HII regions. We find that the dust masses ofthe GDCs are completely dominated by the cold dust component and range from$\sim$1.1$\cdot$10$^{3}$ - 1.4$\cdot$10$^{4}$ M$_{\odot}$. The GDCs haveeffective temperatures of $\sim$13-23 K and show a distinct cold dust effectivetemperature gradient from the centre towards the outer parts of the stellardisk. We find that the population of GDCs in our catalogue constitutes$\sim$16% of the total dust mass of NGC 300, which we estimate to be about5.4$\cdot$10$^{6}$ M$_{\odot}$. At least about 87% of our GDCs have a highenough average dust mass surface density to provide sufficient shielding toharbour molecular clouds. We compare our results to previous pointed moleculargas observations in NGC 300 and results from other nearby galaxies and alsoconclude that it is very likely that most of our GDCs are associated withcomplexes of giant molecular clouds.