Illuminating a tadpole's metamorphosis II: observing the on-going transformation with ALMA

TL;DR

This study uses ALMA observations to reveal the bipolar molecular outflow from a protostar within a globule in the Carina Nebula, providing insights into star formation and globule evolution.

Contribution

First ALMA detection of a bipolar molecular outflow inside a globule, linking it to the jet-driving protostar and analyzing its morphology and kinematics.

Findings

First direct observation of bipolar outflow within the globule

Globule mass estimated at 1.9 solar masses, with a remaining lifetime of about 4 million years

Evidence of grain growth and cold dust in the protostar's environment

Abstract

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the tadpole, a small globule in the Carina Nebula that hosts the HH 900 jet+outflow system. Our data include $^{12}$CO, $^{13}$CO, C$^{18}$O J=2-1, $^{13}$CO, C$^{18}$O J=3-2, and serendipitous detections of DCN J=3-2 and CS J=7-6. With angular resolution comparable to the Hubble Space Telescope (HST), our data reveal for the first time the bipolar molecular outflow in CO, seen only inside the globule, that is launched from the previously unseen jet-driving protostar (the HH 900 YSO). The biconical morphology joins smoothly with the externally irradiated outflow seen in ionized gas tracers outside the globule, tracing the overall morphology of a jet-driven molecular outflow. Continuum emission at the location of the HH 900 YSO appears to be slightly flattened perpendicular to outflow axis. Model fits to the continuum have a best-fit spectral index of $\sim 2$, suggesting cold dust and the onset of grain growth. In position-velocity space, $^{13}$CO and C$^{18}$O gas kinematics trace a C-shaped morphology, similar to infall profiles seen in other sources, although the global dynamical behaviour of the gas remains unclear. Line profiles of the CO isotopologues display features consistent with externally heated gas. We estimate a globule mass of $\sim 1.9$ M$_{\odot}$, indicating a remaining lifetime of $\sim 4$ Myr, assuming a constant photoevaporation rate. This long globule lifetime will shield the disk from external irradiation perhaps prolonging its life and enabling planet formation in regions where disks are typically rapidly destroyed.