 HIA
 Contents
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Cassiopeia -- 2000-JS |
Galaxy clusters represent the largest gravitationally bound objects in the universe. Detailed morphological studies of galaxy clusters indicate that they are relatively young objects, currently in the formation process. Observations toward these objects reveal that the major components of the clusters are the galaxies, the diffuse, thermal cluster gas, and the dark matter. There is, however, evidence that the intracluster medium also contains magnetic fields distributed through the intracluster gas.
The presence of magnetic fields within the intracluster medium can lead to significant effects on the dynamics, and energy transport throughout the cluster. Embedded magnetic fields can modify the pressure of the intracluster medium, suppress thermal conduction, which may lead to the onset of cooling instabilities, and magnetic fields may even bias the initial mass function of star formation. Therefore, in order to understand the overall picture of the evolution of galaxy clusters, it is necessary to understand the role magnetic fields have played in this evolution.
The most direct method of probing intracluster magnetic fields relies on the Faraday rotation effect. As linearly polarized radiation passes through a magneto-ionic region, the rotation of the plane of polarization displays a characteristic wavelength dependence.
This thesis combines radio and X-ray observations, in a statistical study of Faraday rotation toward a sample of nearby galaxy clusters. A comparison of the Faraday rotation measures of sources viewed through the intracluster medium, to the rotation measures of sources falling beyond the edge of the X-ray emitting gas, reveals the presence of excess Faraday rotation in the former sample. This excess rotation is interpreted as originating in the diffuse intracluster medium.
A detailed investigation of the Faraday rotating medium indicates that the Faraday screen is well represented by a model of Faraday cells distributed through the intracluster medium. An analysis of the cluster impact parameter distribution over the rotation measure sample indicates that the Faraday cell scales vary from < 1 kpc in the central regions of the clusters, to over 100 kpc at large impact parameter. Further, the rotation measure distribution indicates the widespread existence of intracluster magnetic fields out to the edges of the X-ray emitting gas. The overall distribution of magnetic field strengths inferred from the data suggests that the fields may play a dynamically important role in the evolution of galaxy clusters.
The first part of this thesis describes the construction of a high resolution (~1 arcminute) atlas of mid-infrared emission along part of the Galactic plane using Infrared Astronomical Satellite (IRAS) data processed using the HIRES algorithm. This emission generally arises from the smallest dust components in the interstellar medium (ISM) and is bright near HII regions due to the enhanced radiation field. The atlas (MIGA: Mid-Infrared Galaxy Atlas) has been combined with radio and far-infrared data as part of the Canadian Galactic Plane Survey.
The remainder of the thesis presents the results of multiwavelength studies using MIGA. An accurate study of dust associated with HII regions requires a careful study of all of the components of an HII region and the surrounding ISM. A comparative study of the mid-infrared and radio continuum morphology of HII regions is presented. Understanding of this morphology is critical for the calculation of infrared fluxes and for the accurate association of infrared emission with a given HII region.
Infrared ratio maps are a useful tool to study the properties of interstellar dust, but the construction of these maps is a non-trivial task with HIRES data. A new technique to construct these maps has been developed and is evaluated.
For many HII regions of small angular extent the only available measurements are the global infrared luminosity and radio flux. An investigation was made of how much information about the structure of the HII region can be obtained from an analysis of these quantities. Accurate knowledge of the stellar content of an HII region is vital for the quantitative study of dust around HII regions. A new O-star spectral classification line ratio for heavily reddened OB stars has been developed.
The HII region KR 140 is the subject of a multiwavelength study. KR 140 appears to be a region of spontaneous massive star formation. Submillimetre observations reveal complementary information about the dust, molecular cores, and possible protostars.
Finally, infrared colour variations within molecular material surrounding the W5 HII region are investigated and ideas for further projects are presented.
The internal kinematics of a galaxy are closely related to its dynamical mass, and can help place constraints on the type of galaxy that is being observed; in particular, different types of galaxies show characteristic scaling relations of size and velocity width or rotation velocity. In principle, these scaling relations provide clues about the nature of a galaxy independently of any changes in luminosity or morphology that may be caused by bursts of star formation.
This thesis is based on a study of the internal kinematics of luminous starforming galaxies in the 0 < z < 0.8 range, with the aim of investigating the nature of the blue galaxies which cause the largest changes in the luminosity function at z >= 0.5. New kinematic data are analysed for a sample of 30 galaxies from the Canada-France Redshift Survey, most of them with rest-frame (U - V)AB <= 1.2. Unlike most previous studies, target galaxies were selected regardless of size and morphology, from a well-studied magnitude-limited survey (the CFRS). Our sample is therefore representative of the most rapidly changing 1/3 of the galaxy population in the 0 < z < 0.8 range. The 17 galaxies at z > 0.45 have sizes (from HST images) and velocity widths (from emission lines) similar to those of typical local Irregular galaxies or very small late-type Spiral galaxies. This is consistent with their morphologies
This thesis focuses on the elaboration of numerical models of Fe II emission spectra and applications of these models to the interpretation of new observational data. A model of the Fe II atom, which includes the lowest 371 energy levels (up to 11.6 eV) and predicts intensities of 68635 lines, is first developed and then incorporated into the radiative-collisional code Cloudy. The atomic data and numerical methods used to determine level populations are described. The basic equations of ionization and thermal balance, level populations, and radiative transfer are solved self-consistently. Test cases show that the atom goes to local thermodynamical equilibrium in the limits of high particle and radiation densities.
The quantitative models have been applied to simulate emission spectra of H II regions. The general behavior of the Fe II emission lines and their sensitivity to density and radiative pumping conditions are investigated. New spectroscopic observations of the Orion Nebula obtained at the Cerro Tololo Inter-American Observatory are presented. The spectral range is 3498 -- 7468 A. The spectra are of high resolution and sensitivity and result in the most extensive line atlas of the Orion Nebula yet made. More than 400 emission lines have been identified, including 40 forbidden [Fe II] lines. Our theoretical model of Fe II emission is in good agreement with the observational data. The velocity field in the Orion Nebula, which shows a marked dependence on the ionization structure, has been analyzed. An overview is presented of general features of the Fe II spectra of typical quasar Broad Emission Line Regions and the dependence of these features on the basic parameters (density, flux of radiation, microturbulent velocity, the Fe abundance, and Ly-pumping). Calculations of Fe II emission for grids spanning several orders of magnitude in density and ionizing flux are performed in the framework of "locally optimally-emitting clouds." It is shown that strong selection effects are at work.
Due to the richness of the Fe II spectra and their sensitivity to the excitation parameters, the Fe II emission lines provide a powerful tool for diagnostics of physical conditions and Fe abundance in a variety of astronomical objects.
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HIA
Contents
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Cassiopeia -- 2000-JS |