Massive Star Formation: Analysis of the kinematic and physical conditions of massive cores in the infrared dark cloud G28.23-0.19
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Massive stars play an important role in the Universe, affecting the evolution of galaxies and formation of planets. However, it is challenging to observe and investigate the initial stages of their formation. It is therefore of interest to study infrared dark clouds (IRDCs), where massive stars are believed to be born. In this thesis, the kinematic and physical conditions of the IRDC G28.23-0.19 was examined with purpose of analysing its potential to form massive stars. Using a mass surface density map, seven massive cores in the IRDC were identified. A multi-wavelength IR analysis were performed at the wavelengths 4.5, 8, 24 and 70 μm in order to estimate the relative evolutionary stages of the cores. The general lack of emission indicates that the cores likely are quiescent or in an early evolutionary stage. Thereafter, the kinematic structure of the cloud and its cores was examined by analysing the spectra for the J = 1 ! 0 rotational transition for 13CO and C18O, respectively. In general, the cloud seems to be moving with one velocity component at 80 km/s. Moreover, none of the line profiles showed broad wings, indicating an absence of outflow activity in the cloud and therefore possibly early evolutionary stages. Following this, the CO depletion factors for the cloud and its cores were estimated. The obtained values of 2.5−5.3 are lower than those generally found in massive starless cores. This could, contrary to above, potentially indicate a later evolutionary stage. Lastly, a virial analysis was performed. The virial parameters obtained for the cores (6.5−12) could potentially indicate a gravitationally unbound state, and that they might not be likely to undergo massive star formation. In summary, G28.23-0.19, in agreement with earlier studies, shows no clear indication of active formation of massive stars. However, further investigations are needed in order to draw more general conclusions.
Massive stars, massive cores, infrared dark clouds, mass surface density, emission spectrum, column density, depletion, virial analysis.