503 research outputs found
The inner structure of ACDM halos
No full textWe have used high resolution N-body simulations to investigate the internal properties of Cold Dark Matter (CDM) halos with virial masses of M(_200) ~ 10(^10) M(_o) at z = 0, comparable to those of dwarf galaxy halos, forming in the ACDM cosmology. In particular, we have focused on providing accurate constraints on the mass distribution in these objects at ~ 1% of the virial radius, r(_200)-. After a brief introduction (chapter 1), the first part of this thesis is concerned with establishing the conditions under which the distribution of mass in simulated CDM halos is unaffected by finite numerical resolution. In chapter 2, we present results from a comprehensive set of simulations of a single galaxy mass halo in which numerical parameters have been varied systematically in order to determine their impact on the spherically averaged mass profile. Based on these results, we have defined a set of convergence criteria that allow us to identify the radial extent over which the spherically averaged circular velocity profile can be considered reliably resolved to better than 10%. In chapter 3, we have examined the abundance of substructure found in three sets of "converged" simulations, and quantified the effect of increasing mass resolution on the number of resolved subhalos of a given mass. The second part of this thesis is concerned with the detailed analysis of the internal structure and kinematics of the simulated dwarf galaxy halos in our sample. In chapter 4, we analyse the structure and kinematics of the dwarfs for possible redshift dependence, and investigate whether these halos could sustain a gaseous disk. In chapter 5, we concentrate on mass dependent trends by performing a detailed comparison with galaxy and cluster mass halos. Finally, chapter 6 provides a summary of the main findings of this work and highlights aspects that may prove rewarding for further study
Observing Exoplanets in the Near-Infrared from a High Altitude Balloon Platform
No full textAlthough there exists a large sample of known exoplanets, little data exists that can be used to study their global atmospheric properties. This deficiency can be addressed by performing phase-resolved spectroscopy - continuous spectroscopic observations of a planet's entire orbit about its host star - of transiting exoplanets. Planets with characteristics suitable for atmospheric characterization have orbits of several days, thus phase curve observations are highly resource intensive, especially for shared use facilities. In this work, we show that an infrared spectrograph operating from a high altitude balloon platform can perform phase-resolved spectroscopy of hot Jupiter-type exoplanets with performance comparable to a space-based telescope. Using the EXoplanet Climate Infrared TElescope (EXCITE) experiment as an example, we quantify the impact of the most important systematic effects that we expect to encounter from a balloon platform. We show an instrument like EXCITE will have the stability and sensitivity to significantly advance our understanding of exoplanet atmospheres. Such an instrument will both complement and serve as a critical bridge between current and future space-based near-infrared spectroscopic instruments
Stratospheric Ballooning With SPIDER and BIT
No full textStratospheric ballooning is an important platform for astrophysics and cosmology. This work presents the development of Spider, a CMB polarimeter, and BIT, a visible light and near-UV imager, both of which are balloon experiments. Both experiments require gondolas and pointing systems to track or scan on the sky, and their development is an important area of research in the field.
Spider aims to observe the relics of inflation by constraining the tensor to scalar ratio, r. It flew an initial flight in 2014-15 and the data analysis is presented here. This work includes the development of the Spider noise model which is an important component of any CMB analysis. Development work on the second Spider gondola is also presented, preparing it for a second Antarctic campaign in the near future.
BIT is attempting to constrain Ω_m , the energy density of matter and σ_8 , the scale size of early universe fluctuations, through the use of weak lensing. Although no weak lensing data has been obtained yet, this thesis presents the development of the instrument from its earliest stages through its two successful test flights. Specific emphasis is given to the development of the star camera subsystem, which was integral to the success of the project.Ph.D.2020-07-21 00:00:0
Netterfield, Catherine R. E. (Death, 1871-07-31)
No full textAddress: 175 PlumAge at death: 22 moPg 171/1871/17/F W S/Miss./Dr. C. A. Breul/Estep/Spring GroveOriginal record filed in drawer labeled 'Nehm-Nia'
Mapping Submillimetre Polarization with BLASTPol
No full textBLASTPol observes the linearly polarized emission from interstellar dust. Dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. With this measurement, BLASTPol can help resolve long-standing questions about the role of magnetic fields in the beginning of star formation.BLASTPol is a 1.8 m telescope with 288 Herschel/SPIRE-heritage bolometric detectors at 250 μm, 350 μm, and 500 μm. Polarimetric capability was added with photolithographed grids and a stepped half-wave plate. This work outlines the instrument, with a focus on the BLASTbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping.In December 2010 and in December 2012, BLASTPol had two long duration balloon flights. An improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. The overall data analysis procedure is described, along with details of the map maker characterization. Finally, maps are presented for the seven targets observed during the 2012 flight. The 14 square degree map of the Vela~C giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation.Ph.D
Mapping Submillimetre Polarization with BLASTPol
No full textBLASTPol observes the linearly polarized emission from interstellar dust. Dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. With this measurement, BLASTPol can help resolve long-standing questions about the role of magnetic fields in the beginning of star formation.BLASTPol is a 1.8 m telescope with 288 Herschel/SPIRE-heritage bolometric detectors at 250 μm, 350 μm, and 500 μm. Polarimetric capability was added with photolithographed grids and a stepped half-wave plate. This work outlines the instrument, with a focus on the BLASTbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping.In December 2010 and in December 2012, BLASTPol had two long duration balloon flights. An improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. The overall data analysis procedure is described, along with details of the map maker characterization. Finally, maps are presented for the seven targets observed during the 2012 flight. The 14 square degree map of the Vela~C giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation.Ph.D
Design and Optimization of a 1.5m Telescope Balloon Borne Gondola
No full textGigaBIT is the successor of the Balloon-Borne Imaging Testbed (SuperBIT), a 1.5m telescope that operates in the stratosphere. The GigaBIT gondola must support a telescope almost double the size of SuperBIT while still adhering to the mass restrictionset forth by its predecessor as it will be launched with the same balloon. This presents the challenge of designing a lightweight gondola, strong enough to survive the necessary structural safety requirements and rigid enough to allow for sub-arcsecond
pointing. This thesis explores the design process and development of the gondola. This was done using topological optimization to determine the optimal structural geometry of the gondola’s frames. From there, a design was produced, analyzed and
amended rigorously following static analysis results to adhere to the mandatory design specifications set forth by the Gondola Structural Design Requirements. This design represents a foundation for future balloon-borne astronomy.M.A.S
Relative Alignment between the Magnetic Field and Molecular Gas Structure in the Vela C Giant Molecular Cloud Using Low- and High-density Tracers
No full textWe compare the magnetic field orientation for the young giant molecular cloud Vela C inferred from 500 μm polarization maps made with the BLASTPol balloon-borne polarimeter to the orientation of structures in the integrated line emission maps from Mopra observations. Averaging over the entire cloud we find that elongated structures in integrated line-intensity or zeroth-moment maps, for low-density tracers such as 12CO and 13CO J → 1 – 0, are statistically more likely to align parallel to the magnetic field, while intermediate- or high-density tracers show (on average) a tendency for alignment perpendicular to the magnetic field. This observation agrees with previous studies of the change in relative orientation with column density in Vela C, and supports a model where the magnetic field is strong enough to have influenced the formation of dense gas structures within Vela C. The transition from parallel to no preferred/perpendicular orientation appears to occur between the densities traced by 13CO and by C18O J → 1 – 0. Using RADEX radiative transfer models to estimate the characteristic number density traced by each molecular line, we find that the transition occurs at a molecular hydrogen number density of approximately 103 cm−3. We also see that the Centre Ridge (the highest column density and most active star-forming region within Vela C) appears to have a transition at a lower number density, suggesting that this may depend on the evolutionary state of the cloud
Probing Interstellar Grain Alignment with Balloon-borne Submillimeter Observations
No full textThe role that magnetic fields play in regulating star formation is one of the outstanding issues in star formation theory. Magnetic fields in star-forming clouds in our galaxy can be observed by tracing the polarized emission from interstellar dust grains. However the mechanism by which the dust grains align with the magnetic fields is not fully understood. Grain alignment theories (e.g. radiative alignment torques) make predictions for the observed spectrum of the polarized emission, so observations at multiple wavelengths can be used to test these theories. The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) observes polarized dust at 250um, 350um and 500um while suspended from a balloon in the stratosphere above Antarctica. BLASTPol maps the dust polarization signal over entire molecular clouds, with enough angular resolution to trace the cloud sub-structures and protostellar cores. BLASTPol uses an attitude reconstruction system consisting of multiple sensors, including star cameras, sun sensors and rate gyroscopes. This system allows BLASTPol to point in-flight at specific regions on the sky, and allows the telescope’s attitude to be reconstructed post-flight. A similar system was built for SPIDER, a balloon-borne telescope that observes the polarization of the CMB.
The analysis pipeline used to produce science maps is discussed, and science results are presented from BLASTPol’s 2012 observations of the Vela C molecular cloud. The polarization spectrum shows a minimum at 350um, similar to the measurements of previous experiments observing other molecular clouds. No strong correlation is seen between he shape of the polarization spectrum and either the temperature or density of the dust. Analysis of the maps is ongoing, and future work will focus on the diffuse dust in the cloud, which is more suitable to compare with dust models.Ph.D
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