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\ $^3P_2\rightarrow^3P_1$ emission at 52 \micron\ from the massive protostar G11.94-0.62, tracing highly ionized gas. We also detect \OI\ $^3P_2\rightarrow^3P_1$ and $^3P_1\rightarrow^3P_0$ at 63 and 145 \micron\ tracing atomic gas, as well as CO $J=14\rightarrow13$ at 186 \micron\ from highly excited molecular gas. The \OIII\ and \OI\ lines exhibit large line widths ($\sim200$ and $\sim40-80$ \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 $\sim8\times10^{-5}\:M_\odot$ yr$^{-1}$ and an atomic outflow mass flux of $\sim5\times10^{-6}\:M_\odot$ yr$^{-1}$, while the molecular outflow traced by CO has an implied mass flux of $\sim3\times10^{-4}\:M_\odot$ 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 $m_* = 22.4^{+21}_{-11}\:M_\odot$, while the \OIII\ emission implies $m_*\gtrsim30\:M_\odot$ and that the protostar is in the final stages of its accretion.

Figures (11)

• Figure 1: Continuum images of G11.94 from the various wavelengths observed by SOFIA FIFI-LS (this work), Spitzer 2009PASP..121..213C, Herschel (2016AA...591A.149M, OBSIDs: 1342218999, 1342219000), and VLA 1994ASPC...61..165B2012PASP..124..939H. The images are shown in logarithmic scale, normalized to the highest flux in an $80\hbox{$^{\prime\prime}$}\times80\hbox{$^{\prime\prime}$}$ region centered on the source peak. The green cross denotes the source identified as the G11.94 protostar from ALMA continuum. The two black crosses (white in panels XI and XII for clarity) are secondary protostars in the region (both detected with ALMA; see §\ref{['sec:origin']}). Panels V and VI also show the peak of emission at 52 and 63 $\mu$m (blue '$\times$' symbols). The offset between green '+' and blue '$\times$' helps define the "color gradient" (see text). Beam sizes are shown in the bottom left of each panel.
• Figure 2: Continuum-subtracted spectra of the [O iii] $^3P_2\rightarrow^3P_1$ at 51.81 $\hbox{$\mu$m}$, [O i] $^3P_2\rightarrow^3P_1$ and $^3P_1\rightarrow^3P_0$ at 63.18 $\hbox{$\mu$m}$ and 145.5 $\hbox{$\mu$m}$, and the CO $J=14\rightarrow13$ line at 185.99 $\hbox{$\mu$m}$. The velocity is corrected for the source $v_{\rm lsr}$ of 36.2 km s$^{-1}$. The fitted Gaussian lines are shown. For [O i] in the 63 $\mu$m bandpass, the Gaussian profile is fitted over a partial range due to telluric contamination on the red wing. Observed line FWHMs (in km s$^{-1}$) are written in the top right of each panel, as well as FWHMs deconvolved from the intrinsic instrument FWHM. The intrinsic width of the CO line is not able to be ascertained via deconvolution and is listed as zero. Flux tickmarks are plotted in 33% increments of the peak line flux.
• Figure 3: Blue- and red-shifted emission of the [O iii] $^3P_2\rightarrow^3P_1$ at 51.81 $\hbox{$\mu$m}$, [O i] $^3P_2\rightarrow^3P_1$ and $^3P_1\rightarrow^3P_0$ at 63.18 $\hbox{$\mu$m}$ and 145.5 $\hbox{$\mu$m}$, and the CO $J=14\rightarrow13$ line at 185.99 $\hbox{$\mu$m}$. The velocity ranges are $\pm(50-300)$ km s$^{-1}$ for every contour map shown. Contours are shown from 50% to 100% with an increment of 10% of the integrated flux for both blue- and red-shifted velocities, independently. The background images show the normalized continuum at corresponding wavelengths. The beam size is shown at the bottom left corner of each panel.
• Figure 4: Left: Continuum image at 52 $\mu$m highlighted with two sets of 2 sq. pixel apertures in the regions where blue- and red-shifted [O iii] emission is detected. Right: The continuum-subtracted spectra extracted from the apertures in the left panel. Each panel shows the spectra extracted from a pair of apertures indicated by the number. These pairs of apertures are chosen to be at opposite sides from the source, probing the blue- and red-shifted lobes. The peaks of Gaussian profiles fitted from the red and blue wings of the spectra are shown as vertical color-coded bars to highlight the peak velocity of the spectra at both sides of the source, as well as the velocity offset between the two lobes.
• Figure 5: Spectral energy distribution for G11.94. The blue data points are measured by FIFI-LS, while the red points are from other observatories. The black line represents the best-fit model, with a $\chi^2$ value of 0.85.