ALMA view of the L1448-mm protostellar system on disk scales: CH${}_3$OH and H${}^{13}$CN as new disk wind tracers

Abstract

Protostellar disks are known to accrete, however, the exact mechanism that extracts the angular momentum and drives accretion in the low-ionization "dead" region of the disk is under debate. In recent years, magneto-hydrodynamic (MHD) disk winds have become a popular solution. Yet, observations of these winds require both high spatial resolution ($\sim 10$s au) and high sensitivity, which has resulted in only a handful of MHD disk wind candidates so far. In this work we present high angular resolution ($\sim 30$ au) ALMA observations of the emblematic L1448-mm protostellar system and find suggestive evidence for an MHD disk wind. The disk seen in dust continuum ($\sim 0.9$ mm) has a radius of $\sim 23$ au. Rotating infall signatures in H${}^{13}$CO${}^{+}$ indicate a central mass of $0.4\pm 0.1$ M${}_{\odot }$ and a centrifugal radius similar to the dust disk radius. Above the disk, we unveil rotation signatures in the outflow traced by H${}^{13}$CN, CH${}_3$OH, and SO lines and find a kinematical structure consistent with theoretical predictions for MHD disk winds. This is the first detection of an MHD disk wind candidate in H${}^{13}$CN and CH${}_3$OH. The wind launching region estimated from cold MHD wind theory extends out to the disk edge. The magnetic lever arm parameter would be $\hat{I}{»}_{\ddot{I}}•\simeq 1.7$, in line with recent non-ideal MHD disk models. The estimated mass-loss rate is $\sim 4$ times the protostellar accretion rate (${\dot{M}}_{\mathrm{acc}}\simeq 2\times 10^{-6}{M}_{\odot }/yr$) and suggests that the rotating wind could carry enough angular momentum to drive disk accretion.

Accepted for publication in A&A