ALTO is a project, currently in the research and development phase, with the goal of constructing a Very High Energy (VHE) gamma-ray observatory in the southern hemisphere. It will detect the particle content reaching the ground from the interactions of either VHE gamma rays or cosmic rays in the atmosphere known as extensive air showers. In this thesis, we use an ALTO prototype built at Linneaus University to estimate the vertical muon intensity in Växjö. The atmospheric muons we detect at ground level come from hadronic showers caused by a cosmic ray entering the atmosphere. Such showers are considered background noise in the context of VHE gamma-ray astronomy, and the presence of muons is an important indicator of the nature of the shower, and thus of the primary particle. The measurement is done by isolating events that produce signals in two small scintillation detectors that are part of the ALTO prototype, and are placed almost directly above each other. This gives us a data set that we assume represents muons travelling along a narrow set of trajectories, and by measuring the rate of such events, we estimate the muon intensity. We estimate the corresponding momentum threshold using two different methods; Monte Carlo simulation and calculation of the mean energy loss. The vertical muon intensity found through this method is about 21% higher than commonly accepted values. We discuss some possible explanations for this discrepancy, and conclude that the most likely explanation is that the isolated data set contains a significant number of “false positives”, i.e., events that do not represent a single muon following the desired trajectory.

The nature of high-energy gamma-ray emission from Star-Forming Galaxies is of utmost importance for understanding both the origin of Cosmic Rays and the high-energy processes that shape galaxy formation. Observations from the gamma-ray telescope Fermi-LAT have detected gamma-ray emission from a handful of nearby Star-Forming Galaxies. Interestingly, observations of the Small Magellanic Cloud show evidence for a spectral cutoff at energies of approximately 10 GeV. This has raised the question as to whether some Star-Forming Galaxies are unable to contain their Cosmic Ray population. Using the Fermitools to analyse the gamma-ray emission from a selection of bright nearby Star-Forming Galaxies, this study intends to explore the possibility of finding further evidence for exponential cutoffs in the gamma-ray spectrum of Star-Forming Galaxies. The shape of the combined spectrum of the 49 galaxies in the sample was determined using least-square fitting of a single power law, a broken power law and a power law with an exponential cutoff. No evidence of an exponentialcutoff was found and the shape of the spectrum was best described by a broken power law with indices Γ1 = -2.48 ± 0.05 and Γ2 = -0.88 ± 0.09. This is in poor agreement with previous observations, which favour a simple power law with an index in the range -2.2 to -2.4. Interestingly, the single power law, while disfavoured over the broken power law at ~7σ, was best fit with the index Γ = -2.35 ± 0.06, which is surprisingly well in agreement with previous observations. The discrepancy between the results presented here and those found in the literature is interpreted as due to insufficient treatment of background fluctuations and the possible existence of bright sources at the unverified blank sky locations used for modelling the background.

High-energy neutrino physics offers a unique way to investigate the most violent phenomena in our universe. The detection of energies above E > 1017 eV is most efficient using the Askaryan effect, where a neutrino-induced particle shower produces coherent radio emission that is detectable with radio antennas. By using radio techniques large volumes can be covered with few stations at moderate cost exploiting the large attenuation length of radio in cold ice. Key to the reconstruction of the neutrino properties visa precise and continuous monitoring of the firn properties. In particular the snow accumulation (changing the absolute depth of the antennas thus the propagation path of the signal) and the index-of-refraction profile are crucial for the neutrino energy and direction reconstruction. This work presents an in-situ calibration design that acts as an detector extension by adding additional emitter antennas to the station design to continuously monitor the firn properties by measuring the direct and reflected signals (D’n’R). In a simulation study the optimal station layout is determined and the achievable precision is quantified. Furthermore 14 months of data from an ARIANNA station at the Ross Ice Shelf, Antarctica, are presented where a prototype of this calibration system has been successfully installed to monitor the snow accumulation with unprecedented precision of 1 mm. Several algorithms, including deep learning algorithms, to compute the D’n’R time difference from radio traces are considered.

The spectroscopic determination of stellar properties is important for subsequent studies of exoplanet atmospheres. In this thesis, HARPS data for 6 exoplanet-hosting, late-type stars is processed to achieve an average signal-to-noise ratio of ~105. Together with line data, the SME tool is used to synthesize spectra and interpolate model photospheres with which chi-square minimization is performed. Fundamental parameters are derived to an overall precision of 191 K in effective temperature, 0.88 dex in surface gravity and 0.21 dex in metallicity. For 5 of the stars, the parameters are thereafter used to compute specific intensities across the stellar discs. Primary improvements could be made in regards to the stellar models, i.a. through the update of atomic properties and inclusion of magnetic fields. The numerical derivation can also be handled more carefully by excluding parameter-insensitive spectral regions. / Den spektroskopiska bestämningen av stjärnegenskaper är viktig för efterföljande studier av exoplaneters atmosfärer. I denna avhandling bearbetas HARPS-data från 6 stjärnor av sen typ som hyser exoplaneter för att uppnå en genomsnittlig signal-till-bruskvot på ~105. Tillsammans med linjedata, används SME-programvaran för att syntetisera spektra och interpolera modellfotosfärer med vilka chi-kvadratminimering genomförs. Fundamentala parametrar härleds till en medelprecision på 191 K i effektiv temperatur, 0.88 dex i ytgravitation och 0.21 dex i metallicitet. För 5 av stjärnorna används parametrarna till att därefter beräkna specifika intensiteter över stjärnornas projicerade ytor. Huvudsakliga förbättringar kan göras med avseende på stjärnmodellerna, bl.a. genom uppdatering av atomära egenskaper och inkludering av magnetiska fält. Den numeriska härledningen kan också hanteras med högre noggrannhet genom att avsiktligt exkludera parameterokänsliga spektralregioner.

This thesis sums up a bachelor project in which gamma-ray emission from an extra-galactic source (S50716+71) is studied using data collected by the Fermi Large Area Telescope (LAT). The emission consists of 12,5 years of data (April 2008 to February 2020) in the energy range 100 MeV - 300 GeV. The source has a high significance (>298) and is believed to be an active galactic nucleus in which there have to be mechanisms able to accelerate photons to these high energies. The mechanisms are believed to be of non-thermal origin and the general consensus is that they are the synchrotron radiation-process as well as the inverse Compton-process. These processes are discussed to some extent in the thesis as part of a fairly large theoretical background. The data was analyzed in several ways. The Enrico software contained in the package Fermitools provided by NASA was used to create curves of the flux as a function of time (lightcurves) as well as spectral distributions. The light curve showed that the source varies considerably with hardly any “quiet periods” at all during the twelve-year period. The light curve also showed a fast rise and fall of intensity between the high intensity and low intensity points. Spectral analyses were made for six chosen time-periods of interest through the fitting of three different functions, a powerlaw-function, a logparabola-function and a powerlaw function with exponential cutoff. The powerlaw function with exponential cutoff was favored in all periods except one where the log parabola-function was preferred. The data from one of the periods was then put into a multi-wavelength context of the source showing that the data is in agreement with previous collected data. This broad spectrum was then used to model the underlying energy distribution through a theoretical framework called the Synchrotron Self-Compton model (SSC). This was done using a modelling software called JetSet. The modelling resulted in a reasonable fit of the data and parameters that overall (at least in magnitude) seem to agree with results from other publications.

The search for extra-terrestrial life is guided by the classification of promising candidate worlds. In this classification the habitable zone acts as a measure for the perceived habitability of a circumstellar body. Habitable zone definitions vary between using a conservative and an optimistic limit. As the Sun progresses through stages of stellar evolution previously uninhabitable outer moons may receive sufficient heating for the existence of liquid water on their surface. To evaluate the possibility for life on these moons the time inside the habitable zone is calculated and compared to estimates for the time for life to develop on Earth. For these calculations the stellar evolution models of PARSEC and Dartmouth are employed. A class of moons is discovered whose time inside the habitable zone is longest during the horizontal branch evolutionary phase (fueled by helium burning in the core). Since the horizontal branch luminosity is near constant, this class is of particular interest due to being less dependent on a stabilizing climate mechanism to regulate atmospheric composition needed to counteract luminosity changes. Ultimately, it is found that regardless of moon, stellar evolution model, and habitable zone definition no post-main sequence time inside the habitable zone is as long as the time for life to arise on Earth. / <p>Research presentation</p>

The Milky Way galaxy, like all spiral galaxies, is surrounded by a roughly spherical distribution of stars called the halo. The halo was largely formed when the galaxy merged with smaller galaxies. The stellar population of the inner halo is dominated by debris from one major such merging event, called the Gaia-Enceladus-Sausage, and the outer halo population is completely built up by several mergers. To properly understand this accretion history, the halo needs to be investigated out to large distances so that as much substructure as possible can be traced. The substructure is expected to leave an imprint in the halo's metallicity structure. In this thesis, we use a catalogue of intrinsically bright stars, giants, to probe the metallicity structure of the halo to large distances. It contains 205,727 stars that all have photometric metallicities from the Pristine survey and distances derived from isochrone fitting, and reaches down to [Fe/H] = -4.0 dex and out to d = 96.16 kpc. Its purity is 90 % and completeness is 67 %. We calculate the distance errors by Monte Carlo simulations and introduce a new cut in colour that is dependent on metallicity to reduce contaminants in the sample. This introduces a metallicity bias in the sample that we can correct for because we coupled metallicity and colour. The correction is done by computing weights for different metallicity bins. The final catalogue allows us to create metallicity distribution functions of the halo as a function of distance. These show us that as heliocentric distance, the distance from the Galactic centre or the Galactic plane increases, the overall metallicity decreases. At the closest distances, the thick disk metallicity peak at -0.7 dex dominates, but as we move further out this smoothly shifts to -1.3 dex and then to -1.6 dex, representing the inner halo, while a peak at -2.2 dex, representing the outer halo, starts to become visible beyond 6 kpc and dominates the metallicity distribution past 26 kpc. These peaks are remnants of merger events in the halo, with the inner halo peak being due to the massive Gaia-Enceladus-Sausage merger and the outer halo peak being due to the many, low-mass and thus low-metallicity galaxies accreted there. We are able to see signals from the Sagittarius stream and Gaia-Enceladus-Sausage's apocentric pile-ups in the metallicity distribution functions, showing that the halo's metallicity changes with not only distance but also sightline. We also detect a diffuse, very metal-poor cloud in the southern footprint that may be an until now unknown structure. This catalogue and its resulting metallicity distribution functions are thus a suitable addition to literature at the metal-poor and distant end, as well as the faint end where e.g. Gaia mission data is unable to provide metallicities and distances. / Vintergatan är, som alla spiralgalaxer, omringad av en ungefärligen sfärisk distribution av stjärnor som kallas halon. Denna halo bildades när galaxen sammansmälte med mindre galaxer. Stjärnpopulationen i den inre halon domineras av stjärnor som kom in med en sådan, väldigt stor, sammanslagning med en annan galax som eter Gaia-Enceladus-Sausage, och den yttre halons stjärnpopulation har helt och hållet byggts upp av sammanslagningar med flera galaxer. För att kunna kartlägga Vintergatans alla sammanslagningar med andra galaxer behöver vi därför undersöka den yttre halon så långt ut som möjligt, för att spåra så mycket substruktur i halon som uppstod till följd av sammanslagningar som möjligt. Sådan substruktur förväntas göra ett avtryck i halons metallicitetsstruktur. I denna masteruppsats används en katalog av intrinsiskt ljusstarka stjärnor, jättar, för att kartlägga halons metallicitetsstruktur till stora avstånd. Katalogen innehåller 205,727 stjärnor som alla har fotometriska metalliciteter från Pristine-undersökningen samt avstånd från isokronanpassning. Den når [Fe/H] = -4.0 dex och d = 96.16 kpc. Mängden jättar i katalogen är 90 % och katalogen behåller 67 % av alla jättar i ursprungskatalogen. Avståndens osäkerhet beräknas med Monte Carlo-simulationer, och det införs ett nytt klipp med färg som är beroende av metallicitet för att undvika kontamination. Detta inför en metallicitetssnedvridning av katalogen som vi kan korrigera eftersom att vi kopplade ihop metallicitet och färg. Korrektionen sker genom att vi beräknar vikter för olika metallicitetsintervall i katalogen. Den slutgiltiga katalogen låter oss skapa metallicitetsdistributioner för halon som beror på avstånd. Dessa distributioner visar oss att när stjärnors avstånd till solen, från galaxens centrum samt från galaxdisken ökar, så minskar den genomsnittliga metalliciteten. Vid väldigt nära avstånd är distributionerna centrerade runt -0.7 dex som motsvarar den tjocka disken, men när avstånden ökar, flyttas denna topp till -1.3 dex och sedan till -1.6 dex, vilket motsvarar den inre halon, samtidigt som en topp vid -2.2 dex, som motsvarar den yttre halon, framträder bortom 6 kpc och dominerar metallicitetsdistributionen för halon bortom 26 kpc. Dessa toppar är kvarlevor efter sammanslagningar mellan Vintergatan och mindre galaxer, där toppen i den inre halon uppstod p.g.a. Gaia-Enceladus-Sausage och toppen i den yttre halon kommer från de många lågmassiva och därmed metallfattiga dvärggalaxer som assimilerats där. Metallicitetsdistributionerna visar signaler från Sagittariusströmmen och Gaia-Enceladus-Sausages apocentriska hopsamlingar, vilket visar att halons metallicitet inte bara beror på avstånd utan även på observationsvinkel. Katalogen visar spår av ett diffust metalfattigt moln i det södra observationsfönstret som potentiellt är en hittills oupptäckt struktur. Denna katalog och dess resulterande metallicitetsdisitributioner är en viktig addering till existerande litteratur i den metallfattiga och avlägsna regimen, samt i den ljussvaga regimen där t.ex. data från Gaiateleskopet inte kan bidra med metallicitets- eller avståndsvärden.

In the standard model of cosmology (ΛCDM) the first stars, star clusters, and galaxies are expected to have formed in short bursts of star formation in low-mass dark matter halos at high redshifts (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%5Csim%20%5C,6-10" data-classname="equation_inline" />). Up to this point, attempts to predict the properties and abundances of these luminous objects have made use of numerically expensive cosmological simulations. On top of being numerically expensive, these simulations often lack the required sub-parsec resolution needed to resolve the formation of compact star clusters and/or neglect possibly dominant stellar feedback processes. Motivated by this, I introduce Anaxagoras, as far as I know the most detailed analytical ab initio model of starbursts in low-mass halos to date. The model incorporates sub-models for gas cooling (including a new determination of the H2-cooling threshold in minihalos), central gas accretion and disk formation (using a new selfsimilarsolution), stellar feedback from radiation pressure (direct stellar radiation, Lyman-<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" data-classname="equation_inline" data-title="" /> scattering in H I, and multiple scattering of IR photons by dust), stellar winds, expanding HII regions, and (crudely) supernovae. The resulting star formation efficiency is used to predict the fraction of stars that remain gravitationally bound in a cluster following gas expulsion, andwhat fraction escape the central region of the halo, yet remain bound by the dark matter halo. I apply Anaxagoras to study star formation at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,6" data-classname="equation_inline" /> in satellite halos of the Milky Way using a halo merger tree code, as well as Population III (Pop III) star formation in minihalos. For the Milky Way setup, hundreds of galaxies are predicted to form with luminosities (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?L_%7B%5Crm%20V%7D%20%5C,%3C%5C,%20%5Crm%7Bfew%7D%5C,%20%5Ctimes%20%5C,%2010%5E4%20%5C:%20%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation_inline" />), half-mass radii (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%2010-200%5C:%5Crm%20pc" data-classname="equation_inline" />), mass-to-light ratios (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M/L_%7B%5Crm%20V%7D%20%5Csim%20100%20-%20%5Crm%7Bfew%7D%20%5C,%5Ctimes%5C,%2010%5E3%20%5C:%5Crm%7BM%7D_%7B%5Codot%7D/%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation" />), and ages (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.18%5E%7B+0.29%7D_%7B-0.31%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" data-title="" />) in good agreement with the observed local population of Ultra-Faint Dwarfs. This shows that ΛCDM is able to explain the properties ofthe faintest dwarf galaxies without fine-tuning. Furthermore, at least ~ 40 compact (initial half-mass radii <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%200.1-5%5C;%5Crm%7Bpc%7D" data-classname="equation_inline" />), old (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.27%5E%7B+0.21%7D_%7B-0.39%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" />) globular cluster (GC) candidates with initial stellar masses <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?10%5E5%20-%2010%5E6%20%5C:%20%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />  are predicted to form at the center of low-mass halos, and could survive to the present-day and explain at least a fraction of the observed metal-poor GCs. Their properties are consistent with recent candidates for GCs residing in dark matter halos. Thus, Anaxagoras lends support to the viability of the scenario of GC formation in minihalos. Finally, the formation of Population III (Pop III) stars in minihalos is studied, with the conclusion that if Pop III stars are not overly massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?25%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />) between ~ 1 − 30 stars could form per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,20" data-classname="equation_inline" />, with the number increasing to ~ 10 − 500 stars per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%3C%5C,15" data-classname="equation_inline" /> as Lyman-Werner feedback delay star formation until halos reach larger masses. In the case where Pop III stars are more massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?140%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" data-title="" />) most minihalos form just a single star. Due to self-shielding of H2 in minihalos, I find that the cosmological Lyman-Werner background is insufficient to produce Pop III galaxies in atomic-cooling halos, with the implication that the number of massive Pop III galaxies/star clusters in the early Universe has been greatly overestimated in the literature that ignores self-shielding.

No description available.

The Pitted Ware culture on Gotland presents a multitude of material that allow archeologists to re-construct and visit the socio-economic structure of a middle-neolithic settlement in the Baltic sea. I will be analyzing the archaeological material in accordance to the ocean, and to what we can interpret as ritual and cosmological variables at the site through ritual theory, and with a method of comparative analogy and research. How maritime aspects of divinity manifested itself to the PWC, ontology and belief system could perhaps reveal how the cognitive, collective mind of one culture evolved and made connections to otherworldly entities. Often in the form of ancestral worship, which will be one of the main issues that will be analyzed and discussed throughout, in addition to mortuary ritual. / Den Gropkeramiska kulturen på Gotland demonstrerar ett extensivt material som tillåter arkeologer att rekonstruera och besöka den socioekonomiska strukturen hos en mellanneolitisk kultur i Östersjön. Jag kommer att analysera materialet i relation till havet, och försöka utgöra havets rituella och kosmologiska kopplingar till lokalen genom ritualteori och en analogisk, komparativ metod. Sättet som maritima aspekter av gudomlighet manifesterade sig inom den Gropkeramiska kulturen på Gotland, dess ontologi och trossystem kan möjligtvis avslöja hur det kollektiva, kognitiva sinnet hos en kultur utvecklades och skapade kontakter till utomvärldsliga ting. Ofta i form av förfädersdyrkan, som tillsammans med begravningsritualer kommer vara ett centralt ämne genom hela uppsatsen.