Early Planet Formation in Embedded Disks (eDisk). XIX. Structures of molecular outflows

TL;DR

The paper addresses how molecular outflows from embedded protostars manifest in high-resolution CO $J=2-1$ emission, seeking a systematic census of outflow morphologies. Using ALMA eDisk data for 19 nearby Class 0/I sources, the authors classify detected CO outflows into wind-driven shells, slow disk winds, and bow shocks, with several sources exhibiting mixtures of these modes. They quantify shell properties with a parametric model, deriving dynamical ages and evidence for time variability and axis changes, and they document frequent misalignments between outflows and disk/continuum axes. The results show SDWs dominate the sample, WS are common, bow shocks are rare, and there is no clear correlation with evolutionary class, highlighting the complexity of accretion–ejection processes and the need for larger, multi-scale surveys to fully understand protostellar feedback and disk-wind launching mechanisms.

Abstract

As part of the ALMA Large Program "Early Planet Formation in Embedded Disks" (eDisk), 12CO (2 - 1) was observed towards 19 nearby low-mass protostars. Of these objects, 15 sources are found to show molecular outflow emission. Based on their morphological and kinematical structures, the CO outflows are classified into three types: a wind-driven shell, where ambient material is swept up by a wide-angle wind from the star, a bow shock, and a slow disk wind, which is a conical or parabolic flow with onion-like velocity structure. We categorize 11 outflows as a slow disk wind, 7 as a wind-driven shell, and 1 as a bow shock. Four of these outflows were found to show signs of both slow disk wind and wind-driven shell characteristics. Five objects show misalignment between the red- and blue-shifted outflows. Seven objects show significant misalignment between the outflow axis (either or both of the red- and blue-shifted outflows) and the minor axis of the dust continuum emission around the protostar. For the objects showing wind-driven shell emission, we compare simple parametrized models with the observations to derive physical properties of the observed shells, such as their dynamical ages. This shows evidence of a time variability in the outflows, such as changes in their direction. In some objects, large differences are seen between the properties of the red- and blue-shifted outflows, possibly indicating differences in the properties of the ambient medium with which the outflow interacts.

Figures (12)

• Figure 1: Categorization of molecular outflows based on the channel map and the P-V diagrams. References: (a) Shu1991Li1996Lee2000Lee2001Arce2002Shang2006 (b) Lee2000Lee2001Cliffe1996Arce2002 (c) Blandford1982Tomisaka1998Machida2008DeValon2022 (d) Hirota2017Tabone2017
• Figure 2: Maps of representative velocity channels (left), position-velocity diagram along the axis of the outflow (top right), and the P-V diagrams perpendicular to the outflow axis at 3$\hbox{$^{\prime\prime}$}$ (middle right) and 6$\hbox{$^{\prime\prime}$}$ from the protostar (bottom right) for Oph IRS 63. This is the best example of an outflow showing wind-driven shell emission in the eDisk sample. The white contours show the 5$\sigma$ level of the emission, where $\sigma$ is the root-mean-square noise level given in Table \ref{['tab:image_properties']}. The channel map is rotated so that the outflow axis is in the vertical direction in the panel. The velocity is also shifted to the relative velocity to the systemic velocity. The position angle of the outflow axis and systemic velocity are listed in Table \ref{['tab:PA_and_Vsys']}. The white dashed lines in the channel map depict the outflow axis and PA$_{\rm cont}$, while the red dashed lines depict the offset positions for the P-V diagrams perpendicular to the outflow axis. Cyan lines depict the model for shell B1 described in § 5.1. The synthesized beam of the observation is shown by the cyan filled ellipse in the bottom left velocity channel map. A scale bar indicating a distance of 200 au is shown in the bottom right velocity map.
• Figure 3: Similar to Figure \ref{['fig:OphIRS63_combined_figure']} but for IRAS15398, the only source in our sample to clearly show jet-driven bow shock emission. The bottom-right panel shows the P-V diagrams perpendicular to the outflow axis at 2$\hbox{$^{\prime\prime}$}$ (middle right) and 14$\hbox{$^{\prime\prime}$}$ (bottom right) from the protostar. The position of the bow shock is indicated by the dotted cyan line at offset=16.6$\hbox{$^{\prime\prime}$}$, while the cyan dotted curve in the P-V diagram along the outflow axis (upper-right panel) shows a schematic emission shape as expected from the bow-shock model.
• Figure 4: Integrated intensity map of $^{12}$CO of IRAS15398 (contours) overlaid on a JWST MIRI image taken with the F1000W filter (colorscale). The contours shown are $3\sigma_{\mathrm{rms}}$, $10\sigma_{\mathrm{rms}}$, $20\sigma_{\mathrm{rms}}$, $30\sigma_{\mathrm{rms}}$, and $40\sigma_{\mathrm{rms}}$, where $\sigma_{\mathrm{rms}} = 150\ \mathrm{mJy\ beam^{-1}\ km\ s^{-1}}$ is the root-mean-square noise of the image. The position of IRAS15398 is indicated by the magenta cross. The south lobe is the same lobe shown in the channel map in Figure \ref{['fig:IRAS15398_combined_figure']}.
• Figure 5: Similar to Figure \ref{['fig:OphIRS63_combined_figure']} but for BHR71 IRS1. This is an example of an outflow showing slow disk wind emission, where the outflow axis is inclined to the plane of the sky. The bottom-right panel shows the P-V diagrams perpendicular to the outflow axis at 3$\hbox{$^{\prime\prime}$}$ (middle right) and 6$\hbox{$^{\prime\prime}$}$ (bottom right) from the protostar.