Early Planet Formation in Embedded Disks (eDisk). XX. Constraining the Chemical Tracers of Young Protostellar Sources

TL;DR

This study provides a uniform, high-resolution view of molecular tracers in 19 nearby Class 0/I protostars, linking emission morphologies to distinct physical components (outflows, cavity walls, inner envelope, disks) and accretion structures. By mapping nine molecules with ALMA at ≈15 au scales, it reveals that outflows dominate $^{12}$CO/13CO emission while rotation is detected in C$^{18}$O and $^{13}$CO in most sources; DCN and CH3OH trace hot inner regions in many Class 0 objects, signaling early hot-core chemistry. Accretion streamers are identified in five systems through C$^{18}$O, SO, and H2CO, highlighting nonaxisymmetric mass delivery and potential shocks at disk-envelope interfaces. The results underscore the chemical complexity of embedded disks and their relevance to early planet formation, showing that CO-based tracers, complex organics, and hydrocarbons together map a multicomponent, dynamic environment in which planets may begin to form even in the embedded phase.

Abstract

Recent studies indicate that the formation of planets in protoplanetary disks begins early in the embedded Class 0/I phases of protostellar evolution. The physical and chemical makeup of the embedded phase can provide valuable insights into the process of star and planet formation. This study aims to provide a thorough overview of the various morphologies for molecular emissions observed on disk scales toward nearby embedded sources. We present high angular resolution (0.1", 15 au) molecular line emissions for $^{12}$CO, $^{13}$CO, C$^{18}$O, SO, SiO, DCN, CH$_3$OH, H$_2$CO, and c-C$_3$H$_2$ towards 19 nearby protostellar sources in the context of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program "Early Planet Formation in Embedded Disks (eDisk)". Emissions in $^{12}$CO are seen towards all sources and primarily trace outflowing materials. A few sources also show high-velocity jets in SiO emission and high-velocity channel maps of $^{12}$CO. The $^{13}$CO and C$^{18}$O emissions are well-known tracers of high-density regions and trace the inner envelope and disk regions with clear signs of rotation seen at continuum scales. The large-scale emissions of $^{13}$CO also delineate the outflow cavity walls where the outflowing and infalling materials interact with each other, and exposure to UV radiation leads to the formation of hydrocarbons such as c-C$_3$H$_2$. Both DCN and CH$_3$OH, when detected, show compact emissions from the inner envelope and disk regions that peak at the position of the protostar. The CH$_3$OH emissions are contained within the region of DCN emissions, which suggests that CH$_3$OH traces the hot core regions. Likewise, a few sources also display emissions in CH$_3$OH towards the outflow. Both SO and H$_2$CO show complex morphology among the sources, suggesting that they are formed through multiple processes in protostellar systems.

Figures (40)

• Figure 1: Illustration of the different components present in an embedded protostellar system.
• Figure 2: Overview of the detection statistics showcasing plots illustrating the number of sources where emissions of each molecule are observed (left) and the number of molecules observed toward each source (right). The dashed regions represent cases where emissions are observed toward a source but are unlikely to be associated with that source.
• Figure 3: Moment 8 maps of $^{12}$CO ($J$=2--1) created using $\geq3\sigma$ emissions toward ten representative eDisk sources. The contour lines display the continuum emission at thresholds of 5$\sigma$, 15$\sigma$, 45$\sigma$, 135$\sigma$, and 320$\sigma$ for each source. The scale bar is located at the bottom left, and the synthesized beam is indicated in white at the bottom-right corner of each image.
• Figure 4: Moment 8 maps of $^{13}$CO ($J$=2--1) created using $\geq3\sigma$ emissions toward five representative eDisk sources. The contours display the continuum emission at the same levels as Figure \ref{['fig:12co_mom8']}. The scale bar is located at the bottom left, and the synthesized beam is indicated in white at the bottom-right corner of each image.
• Figure 5: Zoomed-in moment 8 maps (top) and moment 9 maps (bottom) of C$^{18}$O ($J$=2--1) created using $\geq3\sigma$ emissions toward five representative eDisk sources. The contours display the continuum emission at the same levels as Figure \ref{['fig:12co_mom8']}. The scale bar is located at the bottom left, and the synthesized beam is indicated in white at the bottom-right corner of each image.