The central parsec of the Milky Way at 3.8 micrometer - Kölner UniversitätsPublikationsServer

Muzic, Koraljka (2008). The central parsec of the Milky Way at 3.8 micrometer. PhD thesis, Universität zu Köln. Open Access

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Abstract

The central part of the Milky Way is a unique environment where an interplay of different astrophysical phenomena can be studied, starting from the physics of the interstellar medium, stellar physics and star formation, to high energetic processes associated with the accretion onto the supermassive black hole Sgr A*. In this thesis I focus onto the central parsec of the Milky Way, observed at 3.8 micrometer (L'-band) during several epochs from 2002 to 2007. This particular wavelength is interesting because one can observe the (very dense) Galactic stellar nuclear cluster, as well as the thermal component of the interstellar medium which is not visible at shorter near-infrared wavelengths. Our images revealed a high number of very narrow filamentary structures associated with the streamers of gas and dust (called mini-spiral), and sometimes also with stars. We also detected several stellar sources that are barely observable at shorter wavelengths, but well defined in the dust-dominated L'-band. The goal of this thesis was to use multi-epoch observations in order to measure motions of filamentary structures, as well as of those very red stars. The proper motion analysis allows us to come a step further in understanding the real nature of these enigmatic sources. The high-resolution observations were obtained with the NAOS/CONICA Adaptive Optics system at the ESO Very Large Telescope at Paranal, Chile. The first part of the thesis deals with the narrow dust filaments. The analysis of their morphology and proper motions shows that they are (i) probably not due to a projectional effect and (ii) are influenced by other forces than just the gravitational force of the central black hole. A possible answer to the question of their nature is that they could be the consequence of an interaction between a fast wind (or an outflow) and the local ISM. I present the best candidates for such an outflow and also discuss the possibility that the outflow is in fact collimated. In the second part I investigate a small compact cluster of infrared-excess sources IRS 13N located ~3.5'' from Sgr A*, previously proposed to contain young stellar objects. Our proper motion analysis results in the discovery of a new co-moving group at the Galactic Center (GC). Six sources are showing the same proper motion, meaning that the system is dynamically young. Furthermore, our orbital analysis results in the conclusion that the IRS 13N cluster could not survive a single orbit around Sgr A* without being disrupted. These results speak in favor of IRS 13N stars being the youngest stars ever observed in this environment. The existence of objects younger than 1 Myr would imply that in-situ star formation in the GC and near massive black holes in general is possible. Furthermore, this would also mean that there may exist a mode of star formation in the GC that must not necessarily be related to a star burst and may supply young stars in a more continuous mode.

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Thesis (PhD thesis)

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