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Master Colloquium |
Shampa Bhusal
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Max-Planck-Institut für Radioastronomie
Globules, associated with H II regions, are one of the best laboratories
to study the impact of stellar radiation and feedback from expanding H
II regions on the surrounding medium. First detected by A. D. Thackeray
(1950) in the southern H II region IC 2944, the so-called Thackeray’s
globules are prime examples of such objects. In this thesis, I present
APEX telescope observations of the largest globule in the complex,
Thackeray 1, in low level rotational transition of CO and [CI], together
with an unbiased spectral line survey in the 230 GHz atmospheric window.
I have used this data to probe the physical and chemical conditions of
the molecular gas and the photo dissociation regions (PDR) in Thackeray
1. The velocity resolved CO observations suggest that the largest
globule is the overlap of two separate regions with masses ~ 11 Msun and
3 Msun corresponding to Thackeray 1A and Thackeray 1B, whereas the
continuum dust emission with LABOCA 870 mum reveals an overall mass of ~
19 Msun . The two regions are kinematically separated with velocities of
-20 and -25 km s-1. The line survey reveals for the first time an
unbiased view on the chemical molecular composition of these globules,
with new detection of molecules such as C18O (2–1), H2CO(3 0,3 – 2
0,2 ), SO, HCN, HNC, HCO+, C2H and CS. MCweeds is used to constrain the
column densities and abundances of these species. The incident FUV field
intensity, G0 and hydrogen nucleus volume density n are estimated by
using PDRTool box models constrained by observed CO line ratios. The
data allows to investigate the stability of the globule by estimating
their virial mass and ionization timescale. Both parameters confirm
previous studies, including the HST image result, that the globule
complex, Thackeray 1 is on the verge of breaking up or evaporating.
[Referees: Prof. Dr. Karl Menten, Prof. Dr. Frank Bigiel]