Surveying the Giant H ii Regions of the Milky Way with SOFIA. VI. NGC 3603

Abstract We present our sixth set of results from our mid-infrared imaging survey of Milky Way Giant H ii regions with our detailed analysis of NGC 3603, the most luminous giant H ii (GH ii) region in the Galaxy. We used imaging data from the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) at 20 and 37 μm, which mapped the central ∼8.′5 × 8.′5 infrared-emitting area of NGC 3603 at a spatial resolution of ≲3″. Utilizing these SOFIA data in conjunction with multiwavelength observations from the near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archival data, we investigate the physical nature of individual infrared sources and subcomponents within NGC 3603. For individual compact sources, we used the multiwavelength photometry data to construct spectral energy distributions (SEDs) and fit them with massive young stellar object (MYSO) SED models, and find 14 sources that are likely to be MYSOs. We also detect dust emission from the 3 massive proplyd candidates, as well as from the disk and outflow of the evolved blue supergiant, Sher 25. Utilizing multiwavelength data, we derived luminosity-to-mass ratio and virial parameters for the star-forming clumps within NGC 3603, estimating their relative ages and finding that NGC 3603 is an older GH ii region overall, compared to our previously studied GH ii regions. We discuss how NGC 3603, which we categorize as a cavity-type GH ii region, exhibits a more modest number of MYSOs and molecular clumps when compared to the distributed-type GH ii regions that share similar Lyman continuum photon rates.