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Category : Dark matter (Astronomy)
Languages : en
Pages : 288
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From their unique location in orbit around the Milky Way, dwarf spheroidal galaxies are excellent laboratories for studying dark matter. In this thesis, information from the dynamics of stars in dwarf spheroidal galaxies is used to infer the mass distribution of dark matter in these objects. A more precise measurement of the mass distribution would give us valuable clues about the nature of dark matter and can help us to target dark matter searches. Classically, the mass of a dwarf galaxy is estimated from measurements of the stellar velocity dispersion profile which tells us the width of the stellar velocity distribution at different distances from the galactic centre. Unfortunately, the velocity dispersion profile only constrains the mass of the galaxy at one radius and places little constraint on dark matter models. To improve upon the classic analysis, one can complement information from the velocity dispersion measurements (the second moment of the velocity distribution) with information from higher moments which constrain the shape of the velocity distribution. We relax assumptions made in previous works and develop new methods that for the first time allow us to draw robust conclusions about the ability of higher moments to differentiate between dark matter models that are indistinguishable in the classic analysis. Whilst our methods are not able to verify predictions from cosmological simulations of dark matter, we found that the fourth moment of the velocity distribution can dramatically improve constraints on the mass distribution of dwarf galaxies and can be used to improve the precision of dark matter detection experiments.
Author:
Publisher:
ISBN:
Category : Dark matter (Astronomy)
Languages : en
Pages : 288
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Book Description
From their unique location in orbit around the Milky Way, dwarf spheroidal galaxies are excellent laboratories for studying dark matter. In this thesis, information from the dynamics of stars in dwarf spheroidal galaxies is used to infer the mass distribution of dark matter in these objects. A more precise measurement of the mass distribution would give us valuable clues about the nature of dark matter and can help us to target dark matter searches. Classically, the mass of a dwarf galaxy is estimated from measurements of the stellar velocity dispersion profile which tells us the width of the stellar velocity distribution at different distances from the galactic centre. Unfortunately, the velocity dispersion profile only constrains the mass of the galaxy at one radius and places little constraint on dark matter models. To improve upon the classic analysis, one can complement information from the velocity dispersion measurements (the second moment of the velocity distribution) with information from higher moments which constrain the shape of the velocity distribution. We relax assumptions made in previous works and develop new methods that for the first time allow us to draw robust conclusions about the ability of higher moments to differentiate between dark matter models that are indistinguishable in the classic analysis. Whilst our methods are not able to verify predictions from cosmological simulations of dark matter, we found that the fourth moment of the velocity distribution can dramatically improve constraints on the mass distribution of dwarf galaxies and can be used to improve the precision of dark matter detection experiments.
Author: Justin Inglis Read
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Category :
Languages : en
Pages :
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Author: Jelena Aleksić
Publisher: Springer
ISBN: 3319231235
Category : Science
Languages : en
Pages : 213
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This thesis presents the results of indirect dark matter searches in the gamma-ray sky of the near Universe, as seen by the MAGIC Telescopes. The author has proposed and led the 160 hours long observations of the dwarf spheroidal galaxy Segue 1, which is the deepest survey of any such object by any Cherenkov telescope so far. Furthermore, she developed and completely characterized a new method, dubbed “Full Likelihood”, that optimizes the sensitivity of Cherenkov instruments for detection of gamma-ray signals of dark matter origin. Compared to the standard analysis techniques, this novel approach introduces a sensitivity improvement of a factor of two (i.e. it requires 4 times less observation time to achieve the same result). In addition, it allows a straightforward merger of results from different targets and/or detectors. By selecting the optimal observational target and combining its very deep exposure with the Full Likelihood analysis of the acquired data, the author has improved the existing MAGIC bounds to the dark matter properties by more than one order of magnitude. Furthermore, for particles more massive than a few hundred GeV, those are the strongest constraints from dwarf galaxies achieved by any gamma-ray instrument, both ground-based or space-borne alike.
Author: Chiara Giuri
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Category :
Languages : en
Pages : 0
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In the last century, several astronomical measurements have supported that a significant percentage (about 22%) of the total mass of the Universe, on galactic and extragalactic scales, is composed of a mysterious "dark" matter (DM). DM does not interact with the electromagnetic force; in other words it does not reflect, absorb or emit light. It is possible that DM particles are weakly interacting massive particles (WIMPs) that can annihilate (or decay) into Standard Model (SM) particles, and modern very- high-energy (VHE; > 100 GeV) instruments such as imaging atmospheric Cherenkov telescopes (IACTs) can play an important role in constraining the main properties of such DM particles, by detecting these products. One of the most privileged targets where to look for DM signal are dwarf spheroidal galaxies (dSphs), as they are expected to be high DM-dominated objects with a clean, gas-free environment. Some dSphs could be considered as extended sources, considering the angular resolution of IACTs; their angu- lar resolution is adequate to detect extended emission from dSphs. [...].
Author: Raphaël Errani
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Category :
Languages : en
Pages :
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ISBN:
Category :
Languages : en
Pages : 30
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Category :
Languages : en
Pages :
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Author: John Raymond Jardel
Publisher:
ISBN:
Category :
Languages : en
Pages : 356
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Although exotic objects like supermassive black holes (SMBHs) and dark matter halos do not emit or interact with light, we can still detect them across the vastness of space. By observing the gravitational dance of objects we can see, astronomers are able to infer the mass of the invisible objects they orbit. This has led to the discovery that nearly every massive galaxy hosts a SMBH at its center, and has confirmed that every galaxy is embedded in an extended halo of dark matter. However, the practice of inferring mass from the motions of bright kinematics tracers has many complications, not the least of which is that we seldom observe more than the line-of-sight component of the instantaneous velocity of a star. Consequently, astronomers must build dynamical models of the galaxies they wish to study. These models often rely on overly restrictive assumptions, or are crippled by degeneracies amongst their parameters and lack predictive power. In this thesis, I introduce a significant advancement into the field of dynamical modeling. My modeling technique is based on the powerful principle of orbit superposition, also known as Schwarzschild Modeling. This technique is robust to many of the degeneracies associated with dynamical modeling, and has enjoyed much success in measuring the SMBHs and dark matter halos of large elliptical or bulge-dominated galaxies. I use it in Chapter 2 to accurately measure the SMBH in the Sombrero Galaxy (NGC 4594) and to constrain its dark matter halo. Unfortunately, when measuring dark matter halos with Schwarzschild Modeling, the modeler is required to adopt a parameterization for the dark matter density profile. Often this is precisely the quantity one wishes to measure. To avoid this reliance on a priori parameterizations, I introduce a technique that calculates the profile non-parametrically. Armed with this powerful new technique, I set out to measure the distribution of dark matter in the halos of some of the smallest galaxies in the Universe. These dwarf spheroidal galaxies (dSphs) orbit the Milky Way as satellites, and their dark matter content has been studied extensively. However, the models used to probe their halos have been simplistic and required overly restrictive assumptions. As a result, robust conclusions about their dark matter content have remained elusive. Into this controversial and active area of study, I bring Non-Parametric Schwarzschild Modeling. The results I find offer the most robust and detailed measurements of the dark matter profiles in the dSphs to date. I begin my study with the first application of standard Schwarzschild Modeling to any dSph galaxy by using it in Chapter 3 on Fornax. This chapter details the process of re-tooling Schwarzschild Modeling for the purpose of measuring these small galaxies. In Chapter 4, I introduce the fully non-parametric technique, and apply it to Draco as proof of concept. Chapter 5 presents the main results of this thesis. Here I apply Non-Parametric Schwarzschild Modeling to Draco, Carina, Fornax, Sculptor, and Sextans. By relaxing the assumption of a parameterization for the dark matter profile, I find a variety of profile types in these five galaxies---some of which are consistent with past observations, others consistent with predictions from simulations, and still others were completely unanticipated. Finally, in Chapter 6 I describe the modeling of these galaxies in more detail. I demonstrate the accuracy of Non-Parametric Schwarzschild Modeling by recovering a known dark matter profile from artificial simulated data. I also expound upon the modeling results by presenting the detailed orbit structure of the five dSphs. Lastly, I compare my results to hydrodynamical simulations to explore the link between dark matter profile type and the baryon content of the dSphs.
Author:
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ISBN:
Category :
Languages : en
Pages : 8
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ISBN: 9789176492246
Category :
Languages : en
Pages : 124
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