Master thesis defense by Andreas Rasmussen Kjær

Revealing the Physical Nature of Streamers Through Simulations and Observations

Abstract

Traditional models assume a dense core collapses symmetrically to form a protostar and disk in isolation. Recent advancements in computational and observational capabilities have uncovered asymmetric flows of material towards disks, commonly referred to as "streamers", that potentially deliver material from outside of the initial collapsing core.

They have been observed around Young Stellar Objects (YSOs) at different evolutionary stages; however, it remains unclear whether these emission signatures correspond to density enhancements or are simply an effect of temperature enhancements in the surrounding envelope. We investigate the physical properties of streamers and the origin of their emission signature.

We further examine whether the streamers identified in observations correspond to those identified in simulation data. We create synthetic observations in 13CO, C18O, and H2CO of zoom-in simulations of eight low-mass protostars, which emulate how the Atacama Large Millimeter/submillimeter Array (ALMA) would observe our systems.

Based on four real ALMA observations, we divide identified streamer candidates into three morphological categories and investigate their physical properties using the simulation data. We identify 42 streamer candidates and match their morphology to the three categories. From the simulation data, we infer that the candidates are denser than the surrounding environment but do not exhibit significant temperature differences.

They exhibit an infalling velocity profile in emission and are bound to the central system. This is consistent with classical free-fall trajectory models on observations of streamers. However, mass inferred from emission systematically underestimates the true mass due to the treatment of ice in the simulation data. We conclude that streamers identified in emission correspond to the density enhancements found in simulation data, and are not a product of temperature enhancements.
 

Supervisors

Troels Haugbølle, Jes K Jørgensen, Maria Teresa Valdivia-Mena

Censor

Liv Hornkær, AU