Dissertations / Theses on the topic 'Milky Way'
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Gonzalez, Garcia Oscar Alberto. "Unfolding the Milky Way bulge." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-145824.
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Boubert, Douglas Philip. "Fast stars in the Milky Way." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283611.
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I present a comprehensive investigation of fast stars in the Milky Way, from brisk disc stars to stars escaping the Galaxy. My thesis is that fast stars are the smoking guns of extreme stellar collisions and explosions, and so can act as an intermediary to studying these theoretically-unconquered astrophysical processes. In Chapter 1 I give a history of fast stars, address what it means for a star to be fast, and describe the processes that accelerate stars. I concisely summarise the Gaia mission, whose recent data releases heavily influenced this thesis. Supernovae in binary systems can fling away the companion; if a runaway companion can be associated with a supernova remnant, then together they reveal the evolution that led to the supernova. However, these associations are difficult to establish. In Ch. 2, I develop a sophisticated Bayesian methodology to search the nearest ten remnants for a companion, by combining data from Gaia DR1 with a 3D dust-map and binary population synthesis. With Gaia DR2, I will identify companions of tens of supernova remnants and thus open a new window to studying late-stage stellar evolution. It is unknown why 17% of B stars are spinning near break-up; these stars are termed Be stars because of emission lines from their ejected material. Their rapid spin could be due to mass transfer, but in Ch. 3 I show this would create runaway Be stars. I demonstrate using a hierarchical Bayesian model that these exist in sufficient numbers, and thus that all Be stars may arise from mass transfer. The stars escaping the Milky Way are termed hypervelocity stars. In Ch. 4, I overturn the consensus that the hypervelocity stars originated in the Galactic centre by showing that a Large Magellanic Cloud (LMC) origin better explains their distribution on the sky. In Ch. 5 I present three ground-breaking hypervelocity results with Gaia DR2: 1) only 41 of the 524 hypervelocity star candidates are truly escaping, 2) at least one of the hypervelocity stars originates in the LMC, and 3) the discovery of three hypervelocity white dwarf runaways from thermonuclear supernovae.
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Pettitt, Alexander Robert. "The morphology of the Milky Way." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/15997.
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This thesis presents an investigation into the morphological features of the Milky Way, the exact structure of which is somewhat of an unknown. We begin with a discussion of the problem at hand, and a review of the literature and methodology associated with determining Galactic structure (Chapter 1). The methodology of the investigation is to use numerical simulations to reproduce the structure of the interstellar medium (ISM) gas under the effect of gravitational forces that represent possible morphologies of the Milky Way, such as spiral arms and inner bars. The ISM is simulated using smoothed particle hydrodynamics (SPH), which has been tailored to ISM scales by the inclusion of cooling, heating and a simple chemical network, discussed in Chapter 2. The Milky Way is first assumed to be grand design in nature, with analytic potentials representing the various arm and bar components. Simulations are then compared to longitude velocity CO emission observations to assess the quality of the reproduction of Galactic morphology. These results are shown in Chapter 3, where best fitting models have a bar pattern speed within 50-60km/s/kpc, an arm pattern speed of approximately 20km/s/kpc, a bar orientation of approximately 45 degrees,and arm pitch angle between 10-15 degrees. While nearly all observed emission features are reproducible, there is no model that reproduces all simultaneously. Using both bar and arm components together we find a better match to the data, but still no perfect reproduction. Models with two arms lack many of the observed features, but models with four arms produce too much local emission in the inner quadrants. Chapter 4 shows more sophisticated synthetic observations, created using a radiative transfer code. Resulting emission features are broadly in keeping with those seen in observations, the strength of which appears a strong function of gas surface density. The analytic potentials are then replaced by a set of discretised mass components that represent the stellar system, which is the subject of Chapter 5. Using a live N-body disc then allows for the dynamic creation of bar and arm features, from which further synthetic observations are produced. Transient arm and bar features are relatively easy to produce, though not necessarily simultaneously. Arm patterns showing two to five arms and some with an effectively flocculent structure are created, with pitch angles around 20 degrees. The pattern speed of which tends to decrease with radius, highlighting that the arms are material rather than wave-like in nature. Best fitting synthetic observations show that a four-armed spiral pattern provides good agreement with observations, more so than that of the fixed potentials, with clear reproduction of nearly all arm features. However, an inner bar appears necessary to remove excess emission seen towards the Galactic centre, which was not present in these models.
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Fermani, Francesco. "Modelling the Milky Way stellar halo." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:bcd70530-506d-46c2-8c99-7f5b8f08f915.
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We motivate the importance of understanding the kinematics and dynamics of the Milky Way stellar halo both in unravelling the formation history and evolution of our host Galaxy and in the more general context of galaxy dynamics. We present a cleaned picture of the kinematics of the smooth component of the stellar halo: we develop a method to quantify the average distance error on a sample of stars based on the idea of Schoenrich et al. (2012), but adapted so that it uses velocity information only on average. We use this scheme to construct an analytic distance calibration for Blue Horizontal Branch (BHB) field halo stars in Sloan colours and demonstrate that our calibration is a) more accurate than the ones available and b) unbiased w.r.t. metallicity and colour. We measure the rotation of the smooth component of the stellar halo with a tool-set of four estimators that use either only the l.o.s. velocities or the full 3D motion. From two samples of BHB stars from the Sloan Digital Sky Survey, we favour a non-rotating single halo. We critique conflicting results in the literature based on similar samples and trace back the disagreement (either in the sign of rotation or in the morphology of the halo) to sample contaminations and/or neglect account of the halo geometry. We propose a scheme that generalizes any isotropic spherical model to a model where the potential is axisymmetric and the distribution function is a function of the three actions. The idea is to approximate the Hamiltonian as a function of the actions with a library of quadratic fits to surfaces of constant energy in action space and then make explicit the dependence of the energy on the three actions in the ergodic distribution function. The transparency of the physics implied by the model we achieve, should make it possible to combine our spheroidal models to the f(J)-models of Binney (2010) for the disks and of Pontzen & Governato (2013) for the dark-matter halo, and obtain a complete actions-defined dynamical model of the Milky Way Galaxy.
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Widmark, Axel. "Dark Matter in the Milky Way." Licentiate thesis, Stockholms universitet, Fysikum, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-156452.
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Den här licenciatuppsatsen bygger på två vetenskapliga artiklar, varav den första är skriven som ensamförfattare och den andra är skriven tillsammans med Dr. Giacomo Monari. De är båda på temat mörk materia i Vintergatan. Den första artikeln handlar om mörk materia som fångas i solen. Förutsatt att mörk materia består av partiklar som interagerar via den svaga kraften, med en massa av storleksordningen 10--1000 GeV, så kan sådana partiklar kollidera med atomkärnor i solens inre, förlora rörelseenergi och bli gravitationellt bundna. Väl infångad så kommer en mörk materia--partikel att fortsätta kollidera och förlora rörelseenergi tills den har uppnått termisk jämvikt med solens kärna. Givet att infångade och termaliserade mörk materia--partiklar har blivit tillräckligt många till antalet så kan dessa partiklar annihiliera och producera standard modell--partiklar. Neutriner som produceras i en sådan process skulle kunna detekteras i ett neutrinoteleskop på jorden, vilket vore ett sätt att indirekt detektera mörk materia. I artikeln har jag utforskat denna termaliseringsprocess och den tid det tar för en infångad partikel att uppnå termisk jämvikt. Jag har funnit att termaliseringstiden är kort jämfört med solens ålder och kan försummas, utom i vissa finjusterade specialfall. I den andra artikeln har vi utfört en dynamisk mätning av massdensiteten i solens närområde. Astrometri från rymdteleskopet Gaia ger information om stjärnors vertikala hastighetsfördelning och hur deras antaltäthet avtar med avstånd från galaxskivan. Genom att anta jämvikt så kan man relatera dessa två fördelning till varandra genom gravitationspotentialen de rör sig genom, vilket i sin tur ger galaxskivans massfördelning. Först och främst så har vi gjort framsteg i fråga om statistisk modellering; för första gången har mätfel på alla enskilda stjärnor tagits i beaktning. Vi har funnit en massdensitet som stämmer överens med de flesta tidigare mätningar och har även kunnat dra slutsatser om solens position och hastighet i förhållande till galaxskivan.
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Brook, Chris Bryan A., and cbrook@phy ulaval ca. "Chemo-dynamical simulations of the Milky Way." Swinburne University of Technology, 2004. http://adt.lib.swin.edu.au./public/adt-VSWT20050323.121320.
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Using a state of the art galaxy formation software package, GCD+, we model the formation and evolution of galaxies which resemble our own Galaxy, the Milky Way. The simulations include gravity, gas dynamics, radiative gas cooling, star formation and stellar evolution, tracing the production of several elements and the subsequent
pollution of the interstellar medium. The simulations are compared with observations
in order to unravel the details of the Milky Way's formation. Several unresolved issues regarding the Galaxy's evolution are specifically addressed. In our first study, limits are placed on the mass contribution of white dwarfs to the dark matter halo which envelopes the Milky Way. We obtain this result by comparing the abundances
of carbon and nitrogen produced by a white dwarf-progenitor-dominated halo with the abundances observed in the present day halo. Our results are inconsistent with a white dwarf component in the halo 5% (by mass), however mass fractions of
~1-2% cannot be ruled out. In combination with other studies, this result suggests that the dark matter in the Milky Way is probably non-baryonic. The second component of this thesis probes the dynamical signatures of the formation of the
stellar halo. By tracing the halo stars in our simulation, we identify a group of high-eccentricity stars that can be traced to now-disrupted satellites that were accreted by the host galaxy. By comparing the phase space distribution of these stars in our simulations to observed high-eccentricity stars in the solar neighbourhood, we find devidence that such a group of stars - a 'stellar stream' - exists locally in our own Galaxy. Our next set of simulations demonstrate the importance of strong energy feedback from supernova explosions to the regulation of star formation. Strong feedback
ensures that the building blocks of galaxy formation remain gas-rich at early epochs. We demonstrate that this process is necessary to reproduce the observed low mass and low metallicity of the stellar halo of the Milky Way. Our simulated galaxy is shown to have a thick disk component similar to that observed in the Milky Way through an abrupt discontinuity in the velocity dispersion-versus-age relation for solar neighbourhood stars. This final study suggests that the thick disk forms in a chaotic merging period during the Galaxy's formation. Our thick disk formation scenario is shown to be consistent with observed properties of the thick disk of the
Milky Way.
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Babusiaux, Carine. "Photometric studies of the Milky Way Galaxy." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615732.
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Marasco, Antonino <1984>. "The gaseous halo of the Milky Way." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5210/1/marasco_antonino_tesi.pdf.
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In the last decade, sensitive observations have revealed that disc galaxies are surrounded by multiphase gaseous halos produced by the circulation of gas from the discs to the environment and vice-versa.
This Thesis is a study of the gaseous halo of the Milky Way carried out via the modelling of the HI emission and the available absorption-line data. We fitted simple kinematical models to the HI LAB Survey and found that the Galaxy has a massive (~3x10^8 Mo) HI halo extending a few kiloparsecs above the plane. This layer rotates more slowly than the disc and shows a global inflow motion, a kinematics similar to that observed in the HI halos of nearby galaxies.
We built a dynamical model of the galactic fountain to reproduce the properties of this layer. In this model, fountain clouds are ejected from the disc by SN feedback and - as suggested by hydrodynamical simulations - triggers the cooling of coronal gas, which is entrained by the cloud wakes and accretes onto the disc when the clouds fall back. For a proper choice of the parameters, the model reproduces well the HI data and predicts an accretion of coronal gas onto the disc at a rate of 2 Mo/yr.
We extended this model to the warm-hot component of the halo, showing that most of the ion absorption features observed towards background sources are consistent with being produced in the turbulent wakes that lag behind the fountain clouds. Specifically, the column densities, positions, and velocities of the absorbers are well reproduced by our model.
Finally, we studied the gas content of galaxies extracted from a cosmological N-body+SPH simulation, and found that an HI halo with the forementioned properties is not observed, probably due ti the relatively low resolution of the simulations.
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Marasco, Antonino <1984>. "The gaseous halo of the Milky Way." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5210/.
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In the last decade, sensitive observations have revealed that disc galaxies are surrounded by multiphase gaseous halos produced by the circulation of gas from the discs to the environment and vice-versa.
This Thesis is a study of the gaseous halo of the Milky Way carried out via the modelling of the HI emission and the available absorption-line data. We fitted simple kinematical models to the HI LAB Survey and found that the Galaxy has a massive (~3x10^8 Mo) HI halo extending a few kiloparsecs above the plane. This layer rotates more slowly than the disc and shows a global inflow motion, a kinematics similar to that observed in the HI halos of nearby galaxies.
We built a dynamical model of the galactic fountain to reproduce the properties of this layer. In this model, fountain clouds are ejected from the disc by SN feedback and - as suggested by hydrodynamical simulations - triggers the cooling of coronal gas, which is entrained by the cloud wakes and accretes onto the disc when the clouds fall back. For a proper choice of the parameters, the model reproduces well the HI data and predicts an accretion of coronal gas onto the disc at a rate of 2 Mo/yr.
We extended this model to the warm-hot component of the halo, showing that most of the ion absorption features observed towards background sources are consistent with being produced in the turbulent wakes that lag behind the fountain clouds. Specifically, the column densities, positions, and velocities of the absorbers are well reproduced by our model.
Finally, we studied the gas content of galaxies extracted from a cosmological N-body+SPH simulation, and found that an HI halo with the forementioned properties is not observed, probably due ti the relatively low resolution of the simulations.
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Williams, Rik Jackson. "The warm-hot environment of the Milky Way." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1154972702.
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Uzun, Nezihe. "Free Electron Density Distribution Of The Milky Way." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614312/index.pdf.
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The aim of this study is to determine the free electron density distribution
of the Milky Way Galaxy using dispersion measures of pulsars.
By making use of 1893 Galactic pulsar, 274 supernova remnant and 543 HII
region data, the overall free electron density map of the Galaxy is obtained by
using a 3D mesh-like structure of irregular size.
The main idea behind the study is to treat each 3D section of the Galaxy
privately considering the distance versus dispersion measure graphs of the
pulsars that fall into those sections.
This sectioning procedure is followed using a trial and error method and
results in 348 sections through which free electron densities can be
calculated.
Using linear fits of distance versus dispersion measure graphs, pulsars
that deviate from the curves are investigated and new distances are adopted to
140 of them that are decided to have wrong distance estimates.
By this way both distance values and the free electron densities of the
sections are improved.
In the end, by using the free electron density values of 348 sections, a projected and
cumulative free electron density map of the Galaxy is plotted in polar
coordinates.
This map is compared with three different spiral arm models and it is seen
that the best accordance is with Hou et al. 2009 spiral arm model.
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Jofré, Pfeil Paula. "The age of the milky way halo stars." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-133404.
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García, Fuentes Pablo Fernando. "Giant Molecular Clouds in the Southern Milky Way." Tesis, Universidad de Chile, 2007. http://www.repositorio.uchile.cl/handle/2250/104575.
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Thom, Christopher, and na. "High velocity clouds and the Milky Way Halo." Swinburne University of Technology, 2006. http://adt.lib.swin.edu.au./public/adt-VSWT20060920.101419.
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This thesis presents an exploration of stars and gas in the halo of our Galaxy. A sample
of 8321 field horizontal branch (FHB) stars was selected from the Hamburg/ESO Survey.
The stars make excellent tracers of the Milky Way halo, and we studied the kinematics
of a subset of the HES FHB stars, comparing their velocity dispersions to those predicted
by several models. Since these stars are intrinsically luminous, hot and numerous they
make ideal probes of the distances to high-velocity clouds (HVCs) - clouds of neutral
hydrogen gas whose distances are largely unknown and which do not fit simple models
of Galaxy rotation. A catalogue of stars which align with the HVCs was developed. High
resolution spectroscopy of 16 such HVC probes with the Magellan telescope has yielded
a remarkably tight distance constraint to complex WB. This is one of only a handful of
such distance limits so far established. Lower distance limits were set for several other
clouds. Finally, we have suggested that some of the HVCs may be associated with the
accretion onto the MilkyWay of the Sagittarius dwarf galaxy.
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Thom, Christopher. "High velocity clouds and the Milky Way Halo." Australasian Digital Theses Program, 2006. http://adt.lib.swin.edu.au/public/adt-VSWT20060920.101419/index.html.
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Thesis (PhD) - Swinburne University of Technology, 2006.A dissertation presented in fulfillment of the requirements for the degree of Doctor of Philosophy, Swinburne University of Technology - 2006. Typescript. Bibliography: p. 83-91.
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Häfner, Ralf M. "A dynamical model of the inner Milky Way." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298707.
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Pidopryhora, Yurii. "Extra-Planar HI in the Inner Milky Way." Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1162881965.
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Schönrich, Ralph. "Structure, Kinematics and Chemistry of the Milky Way Galaxy." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-137674.
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Chakrabarty, Dalia. "The solar neighbourhood and centre of the Milky Way." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246400.
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Chatzopoulos, Sotirios. "The old Nuclear Star Cluster in the Milky Way." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-184835.
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Green, Gregory Maurice. "Mapping Milky Way Dust in 3D With Stellar Photometry." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493261.
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I present a three-dimensional map of interstellar dust reddening, covering three-quarters of the sky out to a distance of several kiloparsecs, based on Pan-STARRS 1 and 2MASS photometry. The map reveals a wealth of detailed structure, from filaments to large cloud complexes. The map has a hybrid angular resolution, with most of the map at an angular resolution of 3.4′ to 13.7′ , and a maximum distance resolution of ∼25%. The three-dimensional distribution of dust is determined in a fully probabilistic framework, yielding the uncertainty in the reddening distribution along each line of sight, as well as stellar distances, reddenings and classifications for 800 million stars detected by Pan-STARRS 1. The method developed here compares observed stellar photometry with empirical stellar templates, incorporating prior knowledge about the structure of the Galaxy.
I validate the per-star reddening estimates by comparison with reddening estimates for stars with both SDSS photometry and SEGUE spectral classifications, finding per-star agreement to within ∼0.15 mag out to a stellar E(B−V) of 1 mag. I demonstrate the consistency of the resulting reddening estimates with those of two-dimensional emission-based maps of dust reddening. In particular, I find agreement with the Planck τ353 GHz-based reddening map to within 0.05 mag in E(B−V) to a depth of 0.5 mag, and explore systematics at reddenings less than E(B−V) ≈ 0.08 mag. I compare the 3D map developed here to two existing three-dimensional dust maps, by Marshall et al. (2006) and Lallement et al. (2013), exploring the strengths and weaknesses of the different 3D mapping methods. The map presented here has better angular resolution than both 3D maps compared, and it has better distance resolution than Marshall et al. (2006) within ∼3 kpc, but shows radial “finger-of-God” features not contained in Lallement et al. (2013).
The map can be queried or downloaded at http://argonaut.skymaps.info. I expect the three-dimensional reddening map presented here to find a wide range of uses, among them correcting for reddening and extinction for objects embedded in the plane of the Galaxy, studies of Galactic structure, calibration of future emission-based dust maps and determining distances to objects of known reddening. The method we present is not limited to the passbands of the Pan-STARRS 1 and 2MASS surveys, but may be extended to incorporate photometry from other optical and near-infrared surveys, such as WISE, Spitzer GLIMPSE, UKIDSS, SDSS (where available), and in the future, LSST and Gaia. The method can also be naturally extended to stellar kinematic data, such as that soon to be released by Gaia.Astronomy
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Willman, Beth. "A survey for resolved Milky Way dwarf galaxy satellites /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/5445.
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Chen, Boquan. "Chemical Evolution of the Milky Way and Chemical Tagging." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28835.
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One of the most important unsolved mysteries of astronomy is the formation and evolution of galaxies. The Milky Way is an ideal testbed for testing our understanding of galaxy evolution, as we can directly observe individual stars and their properties, which is generally not possible in external systems. We now have unprecedented access to a chemodynamical view of a large section of the Milky Way. This thesis sheds light on galaxy evolution by linking physical processes involved in galaxy evolution with the observed age and abundances of stars, specifically the build-up of different elements over time and the chemical distribution at different locations in the Milky Way.
The standard tool for studying chemical evolution is a galactic chemical evolution (GCE) model. In this thesis, we treat the Milky Way as a collection of concentric rings representing different radii and ignore azimuthal variation in the Galaxy. We incorporate many physical processes such as gas accretion, star formation and its feedback, stellar evolution, supernova explosion, cooling of gas, and radial mixing of gas and stars into the model. We use the theoretical nucleosynthesis yields to track the production of elements from various nucleosynthesis channels, including Type Ia supernovae (SNe Ia), asymptotic giant branch (AGB) stars, and core-collapse supernovae (CCSN). The first model we build which is based on a previous model with radial mixing is capable of matching a number of observables we see in surveys. For the first time, we qualitatively replicate the chemical distribution in the solar neighbourhood and beyond simultaneously with one set of global parameters.
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Pavel, Michael D. "Magnetic fields in the milky way: near-infrared polarimetry." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12831.
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Thesis (Ph.D.)--Boston UniversityAstronomers have a limited understanding of the large-scale structure of the Galactic magnetic field and its role in the evolution of the interstellar medium (ISM). This understanding derives primarily from Faraday rotation and synchrotron observations which do not probe the cool, dusty ISM. To advance our knowledge of the Galactic magnetic field, this dissertation reports on the application of a different method, near-infrared (NIR) polarization of background starlight, to place new observational constraints on the nature of the Galactic magnetic field and to study the field's role in the evolution of interstellar material. A radiative transfer computer code was developed to predict all-sky starlight polarization observations. Starlight polarimetry predictions were made for several different dynamo-driven magnetic field geometries, assuming that magnetically-aligned interstellar dust grains polarize background starlight. New NIR starlight polarimetry measurements in the outer Galaxy were tested against these predictions. These observations favor disk-symmetric magnetic fields while rejecting disk-antisymmetric magnetic fields. This result contradicts some previous interpretations of all-sky, radio Faraday rotation measurements. The Galactic magnetic pitch angle is constrained to p = -6 ± 2°. The physical orientations of Galactic HII regions, traced by mid-infrared emission, are compared to the large-scale, disk-symmetric Galactic magnetic field geometry derived above. Hydrogen recombination line spectra towards these same objects revealed that many possessed turbulent linewidths. If fluid turbulence decays with time, then it may be used as a relative age indicator. A trend is seen between magnetic alignment and the degree of turbulence in the HII region. This result leads to the development of an observationally-driven HII region magnetic evolutionary sequence. Resolved polarimetry across the face of the galaxy M51 was measured for comparison with the internal, edge-on view of the Milky Way seen from Earth. Strong upper limits ( < 0.05% at a resolution of 0.6 arcseconds) were placed on the degree of NIR polarization across the face of M51. These results were combined with resolved optical polarimetry measurements from the literature. Normal polarization mechanisms cannot explain the observed polarization dependence on wavelength.
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Yan, Qingzeng. "Molecular clouds and star formation in the Milky Way." Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/75787.
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Using molecular line observations, this thesis studied the molecular clouds of three typical regions of the Milky Way, which are the Galactic centre, high Galactic latitudes, and the Galactic plane. The properties of molecular clouds show remarkable variations among these three regions, which explains why the star formation activities are so different.
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Deul, Erik Ronald. "Interstellar dust and gas in the Milky Way and M33." Leiden : Sterrewacht Leiden, 1988. http://catalog.hathitrust.org/api/volumes/oclc/18547726.html.
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Grimm, Hans-Jakob. "X-ray binaries in the Milky Way and other galaxies." Diss., lmu, 2003. http://nbn-resolving.de/urn:nbn:de:bvb:19-12790.
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Jonas, Justin Leonard. "The 2326 MHZ radio continuum emission of the milky way." Thesis, Rhodes University, 1999. http://hdl.handle.net/10962/d1005235.
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The Rhodes/HartRAO SKYMAP survey is the highest frequency (2326 MHz) and highest resolution (20 arcmin) large-area pencil-beam survey of the celestial radio continuum emission. The survey covers 67 % of the entire sky and is one of only two radio continuum surveys that cover the southern sky. These attributes make the survey eminently suitable for studying the extended radio continuum emission from the Milky Way. This thesis describes the methodology used to produce the SKYMAP survey map and presents an analysis of the galactic radio continuum emission. Mountfort (1989, PhD thesis, Rhodes University) designed and implemented the original SKYMAP observing and data reduction procedures. These original procedures have been modified and extended to accommodate instrumentation upgrades at HartRAO and take advantage of new computer technologies that have become available. A new procedure was developed to perform the merging of the ten individual target-area maps into a self-consistent combined map without discontinuities at the component map boundaries. Calibration and data quality procedures were devised and implemented in order to validate the temperature scale and pointing accuracy of the map data. The uncertainty in the relative full-beam temperature scale is estimated to be 2 % and the RMS pixel noise is less than 30 mK. The uncertainty in the zero-level of the survey map is conservatively estimated to be 80 mK. The RMS pointing accuracy is better than 1.9 arcmin. The diffuse galactic background (DGB) emission is shown to be consistent with four-arm spiral models for the Milky Way. The Gould Belt system and the galactic warp beyond the solar-circle are seen as non-symmetrical distortions in the DGB. An empirical model of the DGB was subtracted from the 2326 MHz map data in order to accentuate faint, extended radio sources. A new technique was devised to discriminate between thermal and non-thermal radio continuum emission on the basis of FIR/radio flux ratios. This procedure was used to reduce the source confusion near the galactic plane. 42 new shell-like radio sources with angular diameters ranging from 1.6 deg to 26 deg are identified in the SKYMAP 2326 MHz map. These sources are probably large-diameter supernova remnants (SNRs) that partially redress the incompleteness in existing SNR catalogues caused by limited surface brightness selection effects. The shells of some of these faint, extended sources are incomplete towards high-latitudes. This morphology suggests that these objects are breaking out of the galactic disk and are releasing hot gas into the halo. There is no evidence for linear worm- and chimney-like features in the non-thermal galactic emission. The spectral index of the diffuse galactic emission is calculated to be beta = 2.72 +/- 0.18 between 408 MHz and 2326 MHz and beta = 2.95 +/- 0.08 between 2326 MHz and 31 GHz, confirming previous work showing that the synchrotron spectrum steepens with increasing frequency. The high frequency spectral index is used to estimate upper limits on the galactic synchrotron foreground contamination of cosmic microwave background radiation measurements. The high-latitude 2326 MHz galactic emission is shown to correlate weakly with the far-infrared galactic cirrus clouds. This correlation is due to thermal free-free radio emission from extended, low-density HII regions associated with the cirrus dust. The RMS level of this thermal signal is estimated to be 1 mK at 2326 MHz. Two further experiments that need to be performed in order to complete the SKYMAP project are discussed: (a) the region of sky near the southern equatorial pole (SEP) needs to be mapped at HartRAO to complete the coverage of the entire southern sky, and (b) independent horn telescope (broad-beam) measurements of the sky temperature are required in order to reduce the baseline uncertainties in the current SKYMAP data.
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Supper, Michelle Abbie. "Investigating the soft X-ray background of the Milky Way." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/9626.
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This thesis uses the data from twenty ROSAT and XMM observations to investigate the structures that generate the soft X-ray background of the Milky Way. Ten of these observations lie in the direction of the Loop 1 Superbubble, specifically, within the North Polar Spur, the Northern Bulge, and immediately south of the Galactic Plane. The others are located in the Anti-centre direction, where the X-ray background is less complex. Using a novel processing technique, point sources and enhancements were successively removed from the observations until only the Diffuse X-ray Background (DXRB) re¬mained. By modelling the spectra of this clean data, and separately analysing the 0 and 0 viii emission lines, the various structures in the DXRB were identified, and their properties determined. The resulting models strongly indicate the existence of three previously unidentified components: a 14 pc thick, 0.1 keV shell surrounding Loop I, an inhomogeneous 0.25 keV Galactic Halo, and a non-thermal component present in the Galactic Centre direction. In contrast with previous work, no evidence was found for a cool Galactic Halo. The centre of Loop I was placed 290 pc away, 80 pc farther than previously believed. Additionally, an ongoing interaction was discovered between the Local Hot Bubble and Loop I.
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Golubov, Oleksiy [Verfasser], and Andreas [Akademischer Betreuer] Just. "Modelling the Milky Way Disc / Oleksiy Golubov ; Betreuer: Andreas Just." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/117704000X/34.
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Goodall, Paul Thomas. "Interactions of the microquasar SS 433 with the milky way." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526540.
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Thompson, Kristen Lynn. "ZEEMAN EFFECT STUDIES OF MAGNETIC FIELDS IN THE MILKY WAY." UKnowledge, 2012. http://uknowledge.uky.edu/physastron_etds/12.
Full textAbstract:
The interstellar medium (ISM) of our Galaxy, and of others, is pervaded by ultra low-density gas and dust, as well as magnetic fields. Embedded magnetic fields have been known to play an important role in the structure and dynamics of the ISM. However, the ability to accurately quantify these fields has plagued astronomers for many decades. Unfortunately, the experimental techniques for measuring the strength and direction of magnetic fields are few, and they are observationally challenging. The only direct method of measuring the magnetic field is through the Zeeman effect.
The goal of this dissertation is to expand upon the current observational studies and understanding of the effects of interstellar magnetic fields across various regions of the Galaxy. Zeeman effect observations of magnetic fields in two dynamically diverse environments in the Milky Way are presented: (1) An OH and HI absorption line study of envelopes of molecular clouds distributed throughout the Galaxy, and (2) A study of OH absorption lines toward the Galactic center region in the vicinity of the supermassive black hole Sgr A*.
We have executed the first systematic observational survey designed to determine the role of magnetic fields in the inter-core regions of molecular clouds. Observations of extragalactic continuum sources that lie along the line-of-sight passing through Galactic molecular clouds were studied using the Arecibo telescope. OH Zeeman effect observations were combined with estimates of column density to allow for computation of the mass-to-flux ratio, a measurement of the gravitational to magnetic energies within a cloud. We find that molecular clouds are slightly subcritical overall. However, individual measurements yield the first evidence for magnetically subcritical molecular gas.
Jansky VLA observations of 18 cm OH absorption lines were used to determine the strength of the line-of-sight magnetic field in the Galactic center region. This study yields no clear detections of the magnetic field and results that differ from a similar study by Killeen, Lo, & Crutcher (1992). Our results suggest magnetic fields no more than a few microgauss in strength.
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Su, Meng. "Discovery of Giant Gamma-ray Bubbles in the Milky Way." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10429.
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Based on data from the Fermi Gamma-ray Space Telescope, we have discovered two gigantic gamma-ray emitting bubble structures in our Milky Way (known as the Fermi bubbles), extending \(\sim 50\) degrees above and below the Galactic center with a width of \(\sim 40\) degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum \((dN/dE \sim E^{-2})\) than the inverse Compton emission from known cosmic ray electrons in the Galactic disk, or the gamma-rays produced by decay of pions from proton-ISM collisions. There is no significant difference in the spectrum or gamma-ray luminosity between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; we also found features in the ROSAT soft X-ray maps at \(1.5 - 2 keV\) which line up with the edges of the bubbles. The Fermi bubbles are most likely created by some large episode of energy injection in the Galactic center, such as past accretion events onto the central massive black hole, or a nuclear starburst in the last \(\sim 10 Myr\). Study of the origin and evolution of the bubbles also has the potential to improve our understanding of recent energetic events in the inner Galaxy and the high-latitude cosmic ray population. Furthermore, we have recently identified a gamma-ray cocoon feature within the southern bubble, with a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. If confirmed, these jets are the first resolved gamma-ray jets ever seen.Astronomy
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Mao, Sui Ann. "Magnetic Fields in the Milky Way and the Magellanic Clouds." Thesis, Harvard University, 2011. http://dissertations.umi.com/gsas.harvard:10017.
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This thesis is an observational investigation into the origin of large-scale coherent magnetic fields in the Milky Way and the Magellanic Clouds. I use Faraday rotation measure of both polarized extragalactic sources and that derived from diffuse polarized synchrotron emission as probes of interstellar magnetism. Rotation measure uniquely provides the magnetic field direction in the diffuse interstellar medium, which cannot be achieved using other observing techniques. Using extragalactic source rotation measures behind the Small Magellanic Cloud (SMC), I find a large-scale coherent magnetic field in this irregular galaxy, where the classic dynamo effect is expected to be weak. I suggest that the cosmic-ray driven dynamo, which relies heavily on cosmic ray pressure to generate poloidal fields could be in operation. By analyzing rotation measures derived from diffuse polarized emission from the Large Magellanic Cloud (LMC) simultaneously with rotation measures of 100 extragalactic sources behind it, I conclude that the LMC has a quadrupolar-type magnetic field structure, in accord with predictions from dynamo theories. However, the field amplification time scale of a classic dynamo is too long compared to frequent tidal-triggered star forming episodes experienced by the LMC which can prevent any large-scale coherent field from building up. I propose that the cosmic-ray driven dynamo, which has a much shorter amplification time scale than the classic dynamo, could be the origin of the observed coherent fields in the LMC. The dynamo theory predicts a symmetric vertical magnetic field across the galactic disk for Milky Way-type galaxies. However, based on rotation measures of 1,000 extragalactic sources toward the Galactic poles, I find a lack of vertical field symmetry across the Galactic mid-plane. I suggest that the observed RMs could be the superposition of a symmetric disk field and an anti-symmetric field produced by a separate dynamo effect in the Galactic halo. Furthermore, I demonstrate that existing Galactic halo magnetic field models cannot successfully reproduce extragalactic rotation measures at mid-Galactic latitudes in the second Galactic quadrant. I propose that halo fields consist of magnetic spirals could potentially account for the observed RM pattern.Astronomy
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Neves, Joao Fernando Ciotta. "Simulations of high mass star formation in the Milky Way." Thesis, University of Hertfordshire, 2013. http://hdl.handle.net/2299/10039.
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Massive star formation takes place in the dense cores of molecular clouds where the stars may be obscured at optical wavelengths. An excellent signpost of a massive young stellar object is the presence of an ultra-compact HII region (UCHii), which is a dense photo-ionised cocoon of gas surrounding the newly formed star. The aim of this project is to develop an assembly of numerical tools, caravela, that can simulate realistic data streams representing high-mass star forming regions in our Galaxy. The synthetic output consists in images and photometric point source catalogues, in the IRAS and Herschel wavebands. In an era when large observational surveys are increasingly important, this tool can produce simulated infrared point-source catalogues of high-mass star forming regions on a Galactic scale. The approach used is to construct a synthetic Galaxy of star-forming regions represented by SED templates. The star-forming regions are distributed randomly along a four spiral arm morphology, although a wide range of geometries can be used including rings and different numbers of spiral arms. The caravela code then observes the synthetic Galaxy to produce simulated images and point source catalogues with appropriate sensitivity and angular resolution. caravela was first used to model the simulated Galaxy by constraining the synthetic output to observations made by IRAS. This numerical tool will allow the user to infer physical properties of the Galactic population of high-mass star forming regions from such observations. Second, the selected model was again observed with caravela in Herschel mode. These are therefore predictive results for the future Herschel observations. A model with 4.0×104 compact proto-stars embedded in larger grey-body envelopes (with T = 40 K and linear size scale lIII = 5.0 × 106 AU) is the best-fit model to the IRAS observational data set studied. We found a level of contamination from low- and intermediate-mass objects of " 90%. The modelled data set resulting from the Herschel simulation resulted in the detection of approximately twice as many Herschel objects than IRAS, which is consistent, in a limited way, with the real observed companion clump fraction (CCF) of 0.90 ± 0.07 (Thompson et al., 2006) means that on average there were observed 2 sources per one IRAS source. Our caravela and the real observed CCF are therefore consistent. caravela was coupled with an independent diffuse emission model (Paladini et al., 2007) and the resulting analysis is presented as an interesting seed for the future.
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Zaritsky, Dennis, Denija Crnojević, and David J. Sand. "ARE SOME MILKY WAY GLOBULAR CLUSTERS HOSTED BY UNDISCOVERED GALAXIES?" IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621403.
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The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass-halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined specific frequency of between 0.06 and 0.39 GCs per 10(9)M(circle dot) of total mass, the surviving Milky Way (MW) subhalos with masses smaller than 10(10)M(circle dot) could host as many as 5-31 GCs, broadly consistent with the actual population of outer halo MW GCs, although matching the radial distribution in detail remains a challenge. Using a subhalo mass function from published high-resolution numerical simulations and a Poissonian model for populating those halos with the aforementioned empirically constrained frequency, we find that about 90% of these GCs lie in lower-mass subhalos than that of Eri II. From what we know about the stellar mass-halo mass function, the subhalo mass function, and the mass-normalized GC specific frequency, we conclude that some of the MW's outer halo GCs are likely to be hosted by undetected subhalos with extremely modest stellar populations.
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Gaylard, Michael John. "Radio studies of ionized hydrogen in the southern Milky Way." Thesis, Rhodes University, 1990. http://hdl.handle.net/10962/d1001993.
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This thesis describes the results of a survey of the HI42ɑ recombination line emission at 2.3 GHz from HII regions in the Southern Milky Way, carried out with the 26 m diameter Hartebeesthoek radio telescope. The Galactic Longitude range covered was 290° to 40°. Single recombination lines were detected from 375 positions. Multiple lines were observed towards 90 positions in the inner Galaxy. No line emission could be detected in 28 positions. Continuum antenna temperatures were estimated from drift scans or radio maps observed for the purpose. LTE electron temperatures and turbulent velocities of the HII regions were calculated where possible. The properties of the sample were compared to those observed in HI09ɑ surveys. The lines observed from over 50 positions were first detections, of which half were associated with optically-identified HII regions. In about 150 cases the lines were only the second to be detected from those HII regions. The processes of the radio emission, detection, and analysis were simulated numerically. The detectability of the emission and the magnitude of non-LTE effects and pressure-broadening in multi-component HII regions was predicted and compared to observations. The radio luminosity function of the HII regions was determined over a range of three orders of magnitude in intrinsic brightness for the first time, using techniques which corrected for different types of incompleteness in the samples. The luminosity function was compared to those in five selected spiral galaxies, and shown to lie between those of M33 and M81. An alternate form of the luminosity function was developed for use with a numerical model of the spiral arm structure of the Milky Way. The physical parameters defining the major spiral arms were established by comparing synthesized diagrams of radial velocity versus Galactic Longitude with those actually observed. The faint, extended HII regions S9 and RCW129 in Scorpius, the Barnard Loop in Orion, and S296 in Canis Major were analyzed, using all available data. All the recombination lines from these HII regions were first detections
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Garofalo, Alessia. "Resolved stellar populations in milky way and andromeda's new satellites." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6278/.
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This thesis concerns the study of the variable stars and resolved stellar populations in four recently discovered dSphs, namely, Hercules and Ursa Major I (UMa I), which are UFD satellites of the MW; Andromeda XIX (And XIX) and Andromeda XXI (And XXI), which are satellites of M31. The main aim is to obtain detailed informations on the properties (age, metallicity, distance, and Oosterhoff type) of the stellar populations in these galaxies, to compare them with those of other satellites around the MW and M31, both ''classical'' dSphs and UFDs.
The observables used to achieve these goals are the pulsating variables, especially the RR Lyrae stars, and the color magnitude diagram (CMD) of the resolved stellar populations.
In particular, for UMa I, we combined B, V time-series observations from four different ground-based telescopes (Cassini, TLS, TT1 and Subaru) and for Hercules, we used archival data acquired with the Advanced Camera for Surveys (ACS) on board the HST.
We used, instead B and V times-series photometry obtained with the Large Binocular Telescope (LBT) for And XIX and And XXI .
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Fornieri, Ottavio. "Cosmic-ray transport in the Milky Way and related phenomenology." Doctoral thesis, Università di Siena, 2021. http://hdl.handle.net/11365/1143115.
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In this thesis, we aim at studying some of the open questions regarding the origin of the "Cosmic Rays" (CRs), as well as their transport properties.
The exceptional quality of the experimentally measured cosmic-ray observables, especially at the recently-achieved energies in the range ~O(100 GeV - 1 TeV), started to question the standard picture, based on a "Supernova Remnant"-(SNR)-only origin of the CRs and a diffusive propagation inspired by the "Quasi-Linear Theory" (QLT) of pitch-angle interaction against alfvénic turbulence.
First, we reproduce the most relevant cosmic-ray observables to tune the propagation setup, numerically solving the transport equation with the DRAGON code. On top of this, to account for the rising of the e^+ above ~10 GeV, we fit a primary population of positrons originating in Pulsar Wind Nebulae, in a model-independent setup that considers the uncertainties in the pulsar injections mechanism. Since the all-lepton spectrum is still not reproduced above ~50 GeV --- and in particular the ~TeV break --- we consider the contribution from a nearby source of e^-, and conclude that an old t_{age} ~ 10^5 yr SNR, located between ~600 pc and ~1 kpc, is probably missing from the Catalogues.
Within the hypothesis of such old remnant in its radiative phase contributing to the e^+ + e^-, we search for its signature in the proton flux as well. To do this, we consider a phenomenological propagation setup that reproduces the hadronic spectral hardening at ~200 GeV as a diffusive feature D(E) ~ E^delta(E), and adopt it consistently for the large-scale background and for the nearby source. Within this framework, we account for the all-lepton spectrum, the proton spectrum and the cosmic-ray dipole anisotropy with the same old (t_{age} = 2*10^5 yr), nearby (d = 300 pc) remnant. We highlight that the progressively hardening diffusion coefficient is a crucial ingredient, since, in a single-power-law diffusion scenario, the dipole anisotropy data would be overshot by, at least, one order of magnitude.
Finally, we explore the phenomenological implications of a change of paradigm in the standard cosmic-ray diffusion --- based on wave-particle interaction with Alfvén fluctuations --- considering a non-linear extension of the QLT that enhances the efficiency of CR-scattering with the other "Magneto-Hydro-Dynamic" (MHD) modes. Indeed, assuming the anisotropy of the alfvénic cascade, its scattering rate at all energies below ~100 TeV is not able to confine charged cosmic rays, and the fast magnetosonic modes alone shape the diffusion coefficient that particles experience in the Galaxy. Within such picture, we implement the resulting D(E) in DRAGON2, where two independent zones differently affect the evolution of the MHD cascade: the Halo (L_{Halo} ~ 5-6 kpc) and the Warm Ionized Medium (L_{WIM} ~ 1 kpc). We find that, with a reasonable choice of selected quantities, representing the physics of the environments, we can reproduce the hadronic fluxes, as well as the boron-over-carbon ratio, from ~200 GeV above. We assign to the rising of the "streaming instabilities" the cosmic-ray transport below this energy.
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CATALDO, MADDALENA. "High-Energy Neutrinos and Gamma-rays from the Milky Way." Doctoral thesis, Università degli Studi dell'Aquila, 2021. http://hdl.handle.net/11697/169000.
Full textAbstract:
Hadronic interactions of high energy protons (or nuclei) with ambient medium
represent one of the main processes that produce high-energy neutrinos and TeV
gamma-rays in our Galaxy. They occur both within the sources where cosmic rays
(CR) are accelerated and/or in the interstellar gas contained in our Galaxy. Being
gamma and neutrino production strictly related, it is natural to adopt a multimessenger approach in which their observations are explained within the same framework.
We present updated calculations of the diffuse emission produced by the interaction of CR with the gas contained in the Galactic disk considering also the possibility
of CR spectral hardening in the inner Galaxy, recently emerged from the analysis of
Fermi-LAT data at lower energies. Above TeV energies diffuse and source components are expected to provide comparable contributions and it is difficult to separate
them on observational grounds. Hence we compare our estimates with the total
(diffuse + sources) observed fluxes: IceCube HESE signal for neutrinos, and fluxes
from the Galactic plane measured by Argo-YBJ, H.E.S.S., HAWC and Milagro for the
gamma counterpart. We provide a limit to the fraction of the high energy neutrino
signal observed by IceCube that can be ascribed to a Galactic origin. We demonstrate
that the TeV gamma-ray sky can be used to probe the distribution of Galactic cosmic rays. We state that a potential tension exists between the CR spectral hardening
hypothesis and observational results.
The constraints can be strengthened if the contribution of sources not resolved by
H.E.S.S. is taken into account. The analysis of H.E.S.S. Galactic Plane Survey allows
to infer the properties of Galactic TeV source population. Evaluating the cumulative
flux expected at Earth by the considered population, we show that the H.E.S.S. unresolved sources provide a relevant contribution to the diffuse Galactic emission. By
the population study we infer general information on the total Milky Way such as
its high-energy gamma-ray luminosity and total flux. Finally, in the hypothesis that
the majority of bright sources detected by H.E.S.S. are powered by pulsar activity,
like e.g. pulsar wind nebulae or TeV halos, we estimate the main properties of the
pulsar population.
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Smartt, Stephen John. "The chemical composition of the galaxy from studies of early-type stars." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337030.
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Kulessa, Andrew Stephen. "Our Galaxy and its satellites." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386167.
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Bacchini, Cecilia. "Analytic modelling of the galactic fountain in the Milky Way potential." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11453/.
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Le galassie a spirale, come la Via Lattea, sono caratterizzate dalla presenza di gas freddo e formazione stellare e vengono perciò chiamate star-forming. Per creare nuove stelle è necessaria una sufficiente riserva di gas, la cui disponibilità governa l’evoluzione della galassia stessa. Finora, non è stato individuato con certezza un meccanismo che possa alimentare la formazione di nuove stelle nelle galassie star-forming. Una delle possibili sorgenti di tale gas è l’alone galattico caldo (corona galattica) il cui raffreddamento e successivo accrescimento possono essere stimolati dal processo di fontana galattica. L’esplosione di supernovae porta nubi di gas freddo in orbita al di sopra del disco stellare; queste nubi raggiungono altezze dell’ordine del kiloparsec, interagendo con la corona di gas caldo. Il moto delle nubi all’interno di un mezzo meno denso comporta l’instaurarsi dell’instabilità di Kelvin-Helmholtz, che ’strappa’ gas dalle nubi e causa la condensazione di materia coronale. Quest’ultima viene quindi accresciuta e, ricadendo sul disco, trasferisce nuovo materiale alla galassia e ne alimenta la formazione stellare. Lo scopo di questa tesi è derivare un modello analitico di fontana galattica che consenta di ottenere una formulazione analitica per il tempo orbitale, cioè il tempo richiesto alle nubi per ricadere sul disco galattico. Infatti, più u tempo le nubi impiegano per attraversare il materiale coronale caldo e ricadere sul disco, più materiale viene accresciuto durante l’orbita. Conoscendo i tempi orbitali sarebbe possibile calcolare il tasso di accrescimento legato al fenomeno di fontana e studiarne l’andamento con il raggio del disco. Questo modello potrebbe rivelarsi utile per lo studio dell’impatto della fontana nell’evoluzione globale del disco galattico e della chimica dell’intera galassia.
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Eyre, Andrew McEwan. "On the dynamics of tidal streams in the Milky Way galaxy." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:be113d1c-cff2-4cd5-a51f-40de15af2dce.
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We present a brief history of Galactic astrophysics, and explain the origin of halo substructure in the Milky Way Galaxy. We motivate our study of the dynamics of tidal streams in our Galaxy by highlighting the tight constraints that analysis of the trajectories of tidal streams can place on the form of the Galactic potential. We address the reconstruction of orbits from observations of tidal streams. We upgrade the geometrodynamical scheme reported by Binney (2008) and Jin & Lynden-Bell (2007), which reconstructs orbits from streams using radial-velocity measurements, to allow it to work with erroneous input data. The upgraded algorithm can correct for both statistical error on observations, and systematic error due to streams not delineating individual orbits, and given high-quality but realistic input data, it can diagnose the potential with considerable accuracy. We complement the work of Binney (2008) by deriving a new algorithm, which reconstructs orbits from streams using proper-motion data rather than radial-velocity data. We demonstrate that the new algorithm has a similar potency for diagnosing the Galactic potential. We explore the concept of Galactic parallax, which arises in connection with our proper-motion study. Galactic parallax allows trigonometric distance calculation to stars at 40 times the range of conventional parallax, although its applicability is limited to only those stars in tidal streams. We examine from first principles the mechanics of tidal stream formation and propagation. We find that the mechanics of tidal streams has a natural expression in terms of action-angle variables. We find that tidal streams in realistic galaxy potentials will generally not delineate orbits precisely, and that attempting to constrain the Galactic potential by assuming that they do can lead to large systematic error. We show that we can accurately predict the real-space trajectories of streams, even when they differ significantly from orbits.
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Sanguansak, Nuanwan. "A study of radio continuum emission of the Milky Way Galaxy." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5399/.
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The synchrotron emissivity distribution of the Milky Way Galaxy has been modelled from the 408 MHz allsky survey of Haslam et al.(1982) after separation of its thermal component with the help of IRAS 60 micron emission(Broadbent et al 1989). We have refined the spiral arm pattern in the inner part of the Galaxy by including a bar at the Galactic centre and an updated the Galactic distance scale and obtained fitted free parameters. At 408 MHz, there is very little absorption in the interstellar medium and the line of sight distribution of synchrotron emissivity was inferred mainly from its presumed relationship to the other tracers of spiral structure via these fitted free parameters. At lower frequencies, the absorption of synchrotron emission due to thermal electrons becomes significant and can give direct information of the nonthermal distribution along the line of sight. We have modelled the distribution of thermal electrons according to our synchrotron arm model and an alternative model based on pulsar dispersion measures using the Galactic rotation curve and the surveys of the distribution of Hl66a emission We have then used our synchrotron model applied at lower frequencies including the absorption to compare with the surveys of Dwarakanath et al.(l990) at 34.5 MHz and Jones and Finlay(l974) at 29.9 MHz. The result confirms that the absorption model of the synchrotron emissivity in the Galactic plane is broadly correct and illustrates the potentials of the absorption technique. However we were not able to distinguish the two models of ionised hydrogen spiral structure. To do this, recombination line surveys with improved frequency resolution are required. Using a new value of the cosmic ray gradient in the Galaxy from diffuse gamma-ray emission we obtain the separate variation of magnetic field and cosmic ray electron density. We give the global properties of the thermal and nonthermal emission that our model implies.
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Bubnick, Benjamin Frank. "Massive Stellar Clusters in the Disk of the Milky Way Galaxy." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288378106.
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Geha, Marla, Risa H. Wechsler, Yao-Yuan Mao, Erik J. Tollerud, Benjamin Weiner, Rebecca Bernstein, Ben Hoyle, et al. "The SAGA Survey. I. Satellite Galaxy Populations around Eight Milky Way Analogs." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625799.
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We present the survey strategy and early results of the "Satellites Around Galactic Analogs" (SAGA) Survey. The SAGA. Survey's goal is to measure the distribution of satellite galaxies around 100 systems analogous to the Milky Way down to the luminosity of the Leo I dwarf galaxy (M-r < -12.3). We define a Milky Way analog based on K-band luminosity and local environment. Here, we present satellite luminosity functions for eight Milky-Way-analog galaxies between 20 and 40. Mpc. These systems have nearly complete spectroscopic coverage of candidate satellites within the projected host virial radius down to r(o) < 20.75 using low-redshift gri color criteria. We have discovered a total of 25 new satellite galaxies: 14. new satellite galaxies meet our formal criteria around our complete host systems, plus 11 additional satellites in either incompletely surveyed hosts or below our formal magnitude limit. Combined with 13 previously known satellites, there are a total of 27 satellites around 8 complete Milky-Way-analog hosts. We find a wide distribution in the number of satellites per host, from 1 to 9, in the luminosity range for which there are 5 Milky Way satellites. Standard abundance matching extrapolated from higher luminosities predicts less scatter between hosts and a steeper luminosity function slope than observed. We find that the majority of satellites (26 of 27) are star-forming. These early results indicate that the Milky Way has a different satellite population than typical in our sample, potentially changing the physical interpretation of measurements based only on the Milky Way's satellite galaxies.
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Gonzalez, Garcia Oscar Alberto [Verfasser], and Ortwin [Akademischer Betreuer] Gerhard. "Unfolding the Milky Way bulge / Oscar Alberto Gonzalez Garcia. Betreuer: Ortwin Gerhard." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1025224000/34.
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Clewley, Lee. "Determining the mass of the Milky Way using blue horizontal branch stars." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397180.
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Wolf, Martin. "Indirect Searches for Dark Matter in the Milky Way with IceCube-DeepCore." Doctoral thesis, Stockholms universitet, Fysikum, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-128785.
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Many astronomical observations, including rotational curve measurements of stars and the analysis of the cosmic microwave background, suggest the existence of an invisible matter density content in the Universe, commonly called Dark Matter (DM). Possibly, DM could be of particle nature, where Weakly Interacting Massive Particles (WIMPs) could be a viable DM candidate. The cubic-kilometer sized IceCube neutrino observatory located at the Earth’s South Pole can search indirectly for the existence of DM by detecting neutrino signals from WIMP self-annihilation in the Galactic center (GC) and the Galactic halo (GH). Two main physics analyses were developed and conducted to search indirectly for WIMP self-annihilation in the Milky Way’s GC and GH. Signal hypotheses for different WIMP annihilation channels, WIMP masses and DM halo profiles were tested. The results of both analyses were compatible with the background-only hypothesis for all tested signal hypotheses. Thus, upper limits at the 90% confidence level (C.L.) on the thermally averaged DM self-annihilation cross-section, <σΑv>, were set. Dedicated atmospheric muon veto techniques have been developed for the GC search making such an IceCube analysis possible for the first time. The GC analysis utilized data from 319.7 days of live-time of the IceCube detector running in its 79-string configuration during 2010 and 2011, whereas the GH analysis utilized pre-existing data samples developed for point-like neutrino sources with a live-time of 1701.9 days between 2008 and 2013. The most stringent upper limits on <σΑv> were obtained for WIMP annihilation directly into a pair of neutrinos assuming a Navarro-Frenk-White (NFW) DM halo profile. Conducting the GC and GH analyses for this annihilation channel an upper limit on <σΑv> as low as 4.0 · 10-24 cm3 s-1 and 4.5 · 10-24 cm3 s-1 is set for a 65 GeV and 500 GeV massive WIMP, respectively. These galactic indirect neutrino searches for DM are complementary to the indirect gamma-ray DM searches usually performed on extra-galactic targets like spheroidal dwarf galaxies.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.