SOFIA FORCAST Photometry of 12 Extended Green Objects in the Milky Way

Massive young stellar objects (MYSOs) are known to undergo an evolutionary phase in which high mass accretion rates drive strong outflows. A class of objects believed to trace this phase accurately is the Spitzer GLIMPSE Extended Green Object (EGO) sample, so named for the presence of extended 4.5 um emission on size scales of ~0.1 pc in Spitzer images. We have been conducting a multiwavelength examination of a sample of 12 EGOs with distances of 1 to 5 kpc. In this paper, we present mid-infrared images and photometry of these EGOs obtained with the SOFIA FORCAST instrument, and construct spectral energy distributions (SEDs) for these objects from the near-IR to sub-mm regimes using archival data from the Spitzer GLIMPSE and MIPSGAL, Herschel Hi-GAL, and APEX ATLASGAL surveys. We fit the SEDs using single-component greybody models and three publicly-available radiative-transfer software packages that produce model SEDs in the context of a single massive protostar and compare results. We examine typical stellar temperature and radius results from the three radiative-transfer packages (which rarely converge for a single source) as well as bolometric luminosity (which typically do). We also discuss differences and trends in temperature and inferred mass from dust (ATLASGAL) versus cold gas (single-dish NH3 (1,1) and (2,2) inversion transition) observations. Finally, we discuss the L/M results for our sample (median: 24.7 Lsun/Msun), which suggest that these objects may be in a transitional stage between the commonly-described "IR-quiet" and "IR-bright" stages of MYSO evolution.