From parsec to au scales : zooming-in on the formation of high-mass young stellar objects

In this thesis, I investigate the formation of high-mass young stellar objects (HMYSOs) and the properties of their protostellar jets. My first science chapter is a study of the kinematic and dynamic properties of the 20M HMYSO IRAS 13481-6124 (Fedriani et al. 2018). I measured mass-loss and momentum rates on the order of 10^-4M sun yr-1 and 10^-2Msun yr-1 km s-1, respectively. I used Hi emission lines to perform spectro-astrometry to probe the massive protostellar jet at au-scales and connect it with the parsec-scale jet. In the second science chapter, I study the unique case of G35.2-0.74N, a 10M sun HMYSO (Fedriani et al. 2019). I observe, spatially coincident atomic near-infrared (NIR) and ionised radio jet emission. For the first time, the ionisation fraction from a jet driven by a massive protostar has been measured. The value obtained (~10%) is similar to that found in jets driven by low-mass protostars. This suggests a common launching mechanism, i. e., the jet is launched magneto-centrifugally. It was possible to measure mass-loss and momentum rates on the order of 10-5Msun yr-1 and 10-2Msun yr-1 km s-1, respectively, without relying on assumptions on the ionisation fraction. This study also confirms that the ionisation mechanism is related to shocks instead of UV radiation from the central source. The new method used in this paper, which combines NIR and radio measurements, opens up a new way to measure ionisation fraction of jets for both the low- and high-mass regime. Lastly, the jet and the accretion disc of the driving source of the Herbig-Haro object 135/136, IRAS 11101-5829, was investigated in the third science chapter (Fedriani et al. submitted). I found disc emission, for the first time, in this object revealed by the NIR CO overtone bandhead emission at 2.29 - 2.5 microns. By using our own developed LTE model, I infer that the emission is consistent with a relatively warm (T~3000 K) and dense (NCO~10^22 cm-2) disc. Notably, the model also suggests a geometry different from that inferred in the jet, retrieved from both spectral emission lines and imaging. This implies that the disc emission is reflected off the outflow cavity walls. This approach has been used for the first time in this thesis and indicates that to obtain the correct geometry of the system, one needs both high spectral and spatial resolution to avoid retrieving possible erroneous results. The results presented in this thesis show further observational evidence that the formation of high-mass protostars and their jets are a scaled-up version of their low-mass counterparts and that their properties scale with mass. In light of these results, we are then one step closer to confirm that star formation proceeds in a similar fashion independently of mass.