The SOFIA Massive (SOMA) Star Formation Survey: I. Overview and First Results

James M. De Buizer, Mengyao Liu, Jonathan C. Tan, Yichen Zhang, Maria T. Beltran, Ralph Shuping, Jan E. Staff, Kei E. I. Tanaka, Barbara Whitney

Published 2016-10-17Version 1

We present an overview and first results of the SOFIA Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from $\sim10$-$40\:\rm{\mu}\rm{m}$. These wavelengths trace thermal emission from warm dust that in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based MIR observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blue-shifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang & Tan models, based on the Turbulent Core Model of McKee & Tan, imply the sources have protostellar masses $m_*\sim10$-30$\:M_\odot$ accreting at $\sim10^{-4}$-$10^{-3}\:M_\odot\:{\rm{yr}}^{-1}$ inside cores of initial masses $M_c\sim30$-500$\:M_\odot$ embedded in clumps with mass surface densities $\Sigma_{\rm{cl}}\sim0.1$-3$\:{\rm{g\:cm}^{-2}}$. Fitting Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates $\sim100\times$ smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.