Surveying the Giant HII Regions of the Milky Way with SOFIA: V. DR7 and K3-50

Abstract

We present our fifth set of results from our mid-infrared imaging survey of Milky Way Giant HII (GHII) regions with our detailed analysis of DR7 and K3-50. We obtained 20/25 and 37um imaging maps of both regions using the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). We investigate the multi-scale properties of DR7 and K3-50 using our data in conjunction with previous multi-wavelength observations. Near to far-infrared spectral energy distributions of individual compact infrared sources were constructed and fitted with massive young stellar object (MYSO) models. We find eight out of the ten (80%) compact sources in K3-50 and three out of the four (75%) sources in DR7 are likely to be MYSOs. We derived luminosity-to-mass ratios of the extended radio sub-regions of DR7 and K3-50 to estimate their relative ages. The large spread in evolutionary state for the sub-regions in K3-50 likely indicates that the star-forming complex has undergone multiple star-forming events separated more widely in time, whereas the smaller spread in DR7 likely indicates the star formation sub-regions are more co-eval. DR7 and K3-50 have Lyman continuum photon rates just above the formal threshold criterion for being categorized as a GHII region (10^50 photons/s) but with large enough errors that this classification is uncertain. By measuring other observational characteristics in the infrared, we find that K3-50 has properties more akin to previous bona fide GHII regions we have studied, whereas DR7 has values more like those of the non-GHII regions we have previously studied.

arXiv comment29 pages, 10 figures, accepted for publication in ApJ

References in corpus (26)

• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Dynamic star formation in the massive DR21 filament
• The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
• HARP/ACSIS: A submillimetre spectral imaging system on the James Clerk Maxwell Telescope
• HII Region Metallicity Distribution in the Milky Way Disk
• The Electron Temperature Gradient in the Galactic Disk
• Effect of Dust Extinction on Estimating Star Formation Rate of Galaxies: Lyman Continuum Extinction
• The Stellar Content of Obscured Galactic Giant H II Regions: II. W42
• The Remarkable Mid-Infrared Jet of Massive Young Stellar Object G35.20-0.74
• MSX Mid infrared imaging of massive star birth environments. II: Giant HII regions
• The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results
• Radiation Transfer of Models of Massive Star Formation. I. Dependence on Basic Core Properties
• Investigating the Nature of the Dust Emission around Massive Protostar NGC 7538 IRS 1: Circumstellar Disk and Outflow?
• SOFIA FEEDBACK survey: exploring the dynamics of the stellar wind driven shell of RCW 49
• Galactic H2CO Densitometry I: Pilot survey of Ultracompact HII regions and methodology
• The JCMT 12CO(3-2) Survey of the Cygnus X Region: I. A Pathfinder
• Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
• The Distribution of Mass Surface Densities in a High-Mass Protocluster
• Dense molecular gas toward W49A: A template for extragalactic starbursts?
• The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X
• A multiwavelength study of star formation in the vicinity of Galactic HII region Sh2-100
• Surveying the Giant HII Regions of the Milky Way with SOFIA: I. W51A
• Surveying the Giant HII Regions of the Milky Way with SOFIA: II. M17
• Millimeter and Submillimeter Survey of the R Corona Australis Region
• Magnetic Field Structures in Star Forming Regions: Mid-Infrared Imaging Polarimetry of K3-50
• Surveying the Giant HII Regions of the Milky Way with SOFIA: III. W49A