The SOMA Atomic Outflow Survey. I. An Atomic OI and Highly Ionized OIII Outflow from Massive Protostar G11.94-00.62

Abstract

Massive stars regulate galaxy evolution and star formation through their physical and chemical feedback, but their formation remains poorly understood. Accretion-powered outflows provide important diagnostics of massive star formation. We present first results from the SOMA Atomic Outflow Survey, a far-infrared massive star formation survey using the FIFI-LS instrument on SOFIA. We report detection of \OIII\ ${}^3{P}_2{\to }^3{P}_1$ emission at 52 \micron\ from the massive protostar G11.94-0.62, tracing highly ionized gas. We also detect \OI\ ${}^3{P}_2{\to }^3{P}_1$ and ${}^3{P}_1{\to }^3{P}_0$ at 63 and 145 \micron\ tracing atomic gas, as well as CO $J=14\to 13$ at 186 \micron\ from highly excited molecular gas. The \OIII\ and \OI\ lines exhibit large line widths ($\sim 200$ and $\sim 40-80$ \kms, respectively) and their morphologies are consistent with a wide-angle bipolar outflow. The properties of molecular tracers (${}^{12}$CO, ${}^{13}$CO, C${}^{18}$O, H${}_2$CO, and CH${}_3$OH) observed with ALMA support this interpretation. Ionized nebula and PDR modeling imply an ionized outflow mass flux of $\sim 8\times 10^{-5}{M}_{\odot }$ yr${}^{-1}$ and an atomic outflow mass flux of $\sim 5\times 10^{-6}{M}_{\odot }$ yr${}^{-1}$, while the molecular outflow traced by CO has an implied mass flux of $\sim 3\times 10^{-4}{M}_{\odot }$ yr${}^{-1}$. The mass and momentum flux in the ionized outflow are consistent with the primary disk wind, while the molecular component is mainly swept-up, secondary outflow gas. We also observe G11.94-0.62 with the LBT in the near-infrared, potentially tracing the base of wide-angle outflow cavities. SED modeling implies a protostellar mass $m_{\ast }=22.4_{-11}^{+21}{M}_{\odot }$, while the \OIII\ emission implies $m_{\ast }\gtrsim 30M_{\odot }$ and that the protostar is in the final stages of its accretion.

Accepted to ApJ 2026/03/17. 18 pages, 11 figures, 4 tables