We study the assembly history of the nuclear star cluster in the Milky Way. Dense nuclear star clusters form distinct components in ~75% of nearby galaxies. Because the Milky Way nuclear star... Show moreWe study the assembly history of the nuclear star cluster in the Milky Way. Dense nuclear star clusters form distinct components in ~75% of nearby galaxies. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve its stellar populations and kinematics much better than possible in external galaxies. We study the large-scale stellar kinematics using long-slit spectroscopic data in the near-infrared. We extract stellar kinematic maps from the integrated light, and detect the complex kinematic structure of the star cluster. We set up dynamical models to derive the cluster’s mass. Further, we study stellar populations using integral-field spectroscopic data. From these data we extract more than 1,000 spectra from individual stars. We study the spatial distribution of young and old stars, and the metallicity distribution of cool stars. We found indications for two different formation mechanisms of the Milky Way nuclear star cluster. On the one hand, gas was accreted to the Galaxy’s centre and stars formed in-situ. On the other hand, stars formed in star clusters outside the centre. These star clusters fell into the Galaxy’s nucleus and contributed to the assembly of the Milky Way nuclear star cluster. Show less
De meeste materie in ons Universum is donker. Deze donkere materie vormt de bouwsteen van de grootschalige, kosmische structuren, waarin sterrenstelsels leven. Door zijn botsingloze natuur is... Show moreDe meeste materie in ons Universum is donker. Deze donkere materie vormt de bouwsteen van de grootschalige, kosmische structuren, waarin sterrenstelsels leven. Door zijn botsingloze natuur is donkere materie namelijk beter in staat structuren te vormen dan normale (__baryonische__) materie. Deze structuren bestaan uit vlakken, filamenten en knopen, die samen ook wel het kosmisch web worden genoemd. Sterrenstelsels bewonen de centra van grotere "halo__s" van donkere materie. Deze halo__s zijn zelf niet zichtbaar en het licht uitgezonden door sterrenstelsels kan ons alleen iets vertellen over het binnendeel van deze halo__s. In dit proefschrift trachten we meer over halo__s te weten te komen. Hiertoe maken we gebruik van kosmologische, hydrodynamische simulaties, waarin we niet alleen de donkere maar ook de zichtbare materie meenemen, alsmede alle processen die gedacht worden belangrijk te zijn voor de vorming en groei van sterrenstelsels. Dergelijke simulaties bieden ons de mogelijkheid om het verband tussen zichtbare en donkere materie te verkennen, aangezien beide componenten tegelijk en zelfconsistent worden gesimuleerd. In waarnemingen kan dit verband onderzocht worden door gebruik te maken van zwaartekrachtlenzen. De werking van dergelijke lenzen is gebaseerd op de afbuiging van fotonen (lichtdeeltjes) wanneer deze door een zwaartekrachtspotentiaal reizen. Zodoende ondervindt licht dat van ver in het heelal naar ons toe reist, onderweg verschillende kleine afbuigingen. Als gevolg hiervan zien wij het beeld van de bron als verplaatst, vergroot en verstoord. Het zwaartekrachtlenseffect kan gebruikt worden om verschillende eigenschappen van (materie in) het Universum te meten, waaronder de totale massa en het massaprofiel van halo__s, de vormen van halo__s, de effici_ntie van de vorming van sterrenstelsels en uiteindelijk ook de fundamentele kosmologische parameters van ons Universum. Door gebruik te maken van kosmologische, hydrodynamische simulaties kunnen we ook mogelijke effecten onderzoeken die ons ervan weerhouden om zwaartekrachtlenswerking te gebruiken om de fundamentele eigenschappen van de structuren waaruit ons Universum is opgebouwd, te meten. Show less
This thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their... Show moreThis thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their surrounding PDRs. We focus our studies on two compact HII regions: W3(A) and the Orion Nebula (Chapters 2 and 3, respsectively). Using SOFIA/FORCAST observations, we determine the properties of dust in the ionized gas, their surrounding PhotoDissociation Regions and their parent molecular clouds. One of the most important conclusions of this thesis is that the grain growth can affect the dust size distribution in regions of massive star formation. The large amount of archival data available for Orion allow us to study other important phenomena related to dust in this region, such as the photoelectric heating effect and Lyman alpha heating. The second part of this thesis presents theoretical studies of the properties of the cold neutral medium (CNM) using carbon radio recombination lines (CRRL). Chapters 4 and 5 consists on the complete theory of CRRLs from the level population equation to the radiative transfer equation. Using these models and observations of CRRLs the physical parameters of the CNM can be determined. Show less
In this thesis we present research on the stellar halo of our Galaxy. In particular we focus on measuring the shape and profile of the stellar halo through photometric techniques and main sequence... Show moreIn this thesis we present research on the stellar halo of our Galaxy. In particular we focus on measuring the shape and profile of the stellar halo through photometric techniques and main sequence turnoff point star counts. We also present a cross-correlation algorithm that can detect stellar overdensities in the halo (streams or satellites) in Colour Magnitude Diagrams with only two photometric filters and no control field. We use this algorithm to characterize different streams and the vicinity of Globular clusters in search for associated stellar populations. Finally we also search for new substructure in the Kilo Degree Survey fields of Data Releases 1 and 2 and find signatures of the major substructures known in the halo. Show less
A microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the... Show moreA microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the Standard Model. In this thesis, we undertook a systematic model-independent program of studying the properties of decaying dark matter. By analyzing the experimental data for dwarf spheroidal galaxies it was shown that the X-ray energy range is a preferred region when searching for radiatively decaying dark matter. By analyzing dark matter distributions in different types of galaxies and in galaxy clusters we show that the expected dark matter signal increases slowly with the mass of the object. Therefore, dwarf and spiral galaxies are the observational targets with the optimal signal-to-noise ratio. To probe the theoretically interesting regions of particle physics models we performed a combined analysis of a very large dataset of archival XMM-Newton observations of galaxies. Finally, we discussed an ultimate way to probe the whole parameter space of minimal models of decaying dark matter. We argue that a new X-ray telescope with the narrow energy resolution (comparable to internal width of the line) and large field-of-view is required. Show less
