The overall aim of this thesis is to investigate the environments of AGN, in particular, the density of galaxies in the environments of radio-loud and radio-quiet AGN. This determines whether AGN trace dense environments at high redshifts and whether the environments are important in addressing the problem of radio-loud dichotomy. I extend my research by investigating whether star-formation evolves differently in high-redshift AGN environments compared to the field. I begin by investigating the environments of 169 AGN using Spitzer data at z ∼ 1. I investigate the source density of star-forming galaxies in the environments of radio galaxies, radio-loud quasars and radio- quiet quasars. I do not find any significant overdensity of star-forming galaxies in these environments, although I find tentative evidence for a diff erence in the colours of galaxies in the radio galaxy environments compared to the quasar and field environments. I next use VIDEO data to investigate the environments of the quasars out to z ∼ 3. Firstly, I use a training sample of QSOs and galaxies, which trains a neural network to detect QSOs in the VIDEO data. I detect 274 possible QSOs in the VIDEO data using this method. I am able to determine that the efficiency of the neural network clas- sification is 95 per cent using the training sample. I compare these results to a colour selection method, which detects 88 QSOs in the VIDEO data, and find that the neural network is able to detect ∼ 80 per cent of the colour selected QSOs at Ks = 21. I then investigate the source overdensity using a radial analysis on the environments of the VIDEO QSOs. I find a significant overdensity of galaxies in the environments of the whole QSO sample and in the environments of the radio-loud quasars compared to the radio-quiet quasars. I extend the density analysis by using a second density measure, called the spatial clustering amplitude technique, to compare the environments of the quasars with their radio luminosities, absolute magnitudes and redshifts. I do not fi any significant correlations between environmental density and radio luminosity, absolute magnitude or redshift for the QSOs. I extend this research to investigate the type of galaxies found in the AGN environments. However, I do not find any significant differences between the type of galaxies found in the QSO environments and the background field.

We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emission from high ionization lines that will not be emitted by the Crab’s filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The NIR [Ne VI] λ 7.652 mm line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV λ1549Å doublet is predicted to be the strongest absorption line from the shell, which is in agreement with HST observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually “remember” its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion. Infrared observations have discovered a variety of objects, including filaments in the Crab Nebula and cool-core clusters of galaxies, where the H2 1-0 S(1) line is stronger than the infrared H I lines. A variety of processes could be responsible for this emission. Although many complete shock or PDR calculations of H2 emission have been published, we know of no previous simple calculation that shows the emission spectrum and level populations of thermally excited low-density H2. We present a range of purely thermal collisional simulations, corresponding to constant gas kinetic temperature at different densities. We consider the cases where the collisions affecting H2 are predominantly with atomic or molecular hydrogen. The resulting level population (often called “excitation”) diagrams show that excitation temperatures are sometimes lower than the gas kinetic temperature when the density is too low for the level populations to go to LTE. The atomic case goes to LTE at much lower densities than the molecular case due to larger collision rates. At low densities for the v=1 and 2 vibrational manifolds level populations are quasi-thermal, which could be misinterpreted as showing the gas is in LTE at high density. At low densities for the molecular case the level population diagrams are discontinuous between v=0 and 1 vibrational manifolds and between v=2, J=0, 1 and other higher J levels within the same vibrational manifold. These jumps could be used as density diagnostics. We show how much the H2 mass would be underestimated using the H2 1-0 S(1) line strength if the density is below that required for LTE. We give diagnostic diagrams showing level populations over a range of density and temperature. The density where the level populations are given by a Boltzmann distribution relative to the total molecular abundance (required to get the correct H2 mass), is shown for various cases. We discuss the implications of these results for the interpretation of H2 observations of the Crab Nebula and filaments in cool-core clusters of galaxies.

We present distances and kinematics and look at the possible populations for the blue plume (BP) stars in the Canis Major Overdensity (CMa). We conducted a medium resolution spectral survey on the BP stars (N=303) in CMa (centered at l = 238° ; b = -8°) using the data from AAOmega Spectrograph. We used a modified version of the Statistics-sensitive Non-linear Iterative Peak-clipping (SNIP) algorithm to normalize our fluxed absorption spectra. After determining the radial velocities from measurements of strong absorption features for the stars we use a Bayesian analysis of spectral feature strengths and photometric colors to determine Teff, Logg and [Fe/H]. Our procedure makes use of grid for model synthetic spectra computed using SPECTRUM with Atlas9 model atmospheres and Kurucz model colors. We determine the absolute magnitude using the stellar parameters and BaSTI isochrones and compute distances and ages for the BP stars. Our analysis of the BP stars indicates Teff ranging from 6500K to 8000K, metallicity ranging from 0.0 to -1.0 with an average of -0.5. We found for this temperature range that the surface gravity of the stars could not be well constrained. From the spatial and kinematics results we found that most of the stars are thick disk stars with a small mixture of thin disk stars. The stars are most likely a mixture of thick disk blue stragglers and normal A-type stars preferentially seen to greater depths due to the low dust extinction in this location of the Galaxy.

The mechanisms which cause galaxies to form and evolve each leave behind distinct structural markers in their wake. Dynamically hot processes (e.g., monolithic collapse, hierarchical merging) give rise to pressure-supported spheroidal structures, including elliptical galaxies and classical bulges. By contrast, dynamically cold processes (e.g., gas accretion, AGN splashback) lead to flattened rotationally-supported disk-like structures, often found on their own or as part of a spiral galaxy. If left in isolation for a sufficient length of time, secular evolutionary processes cause the formation of a bar-like structure within the disk, precipitating the genesis of a rotationally-supported pseudo-bulge. Robustly measuring galaxy structure enables us to ascertain the relative importance of these competing evolutionary mechanisms and; in so doing, help broaden our understanding of how the Universe around us came to be. This thesis explores the relation between galaxy structure, morphology and stellar mass. In the first part I present single-Sérsic two-dimensional model fits to 167,600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey (UKIDSS LAS) imaging data available via the Galaxy and Mass Assembly (GAMA) data base. In order to facilitate this study, we developed Structural Investigation of Galaxies via Model Analysis (SIGMA): an automated wrapper around several contemporary astronomy software packages. We confirm that variations in global structural measurements with wavelength arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxies. In the second part of this thesis we establish a volume-limited sample of 3,845 galaxies in the local Universe and visually classify these galaxies according to their morphological Hubble type. We find that single-Sérsic photometry accurately reproduces the morphology luminosity functions predicted in the literature. We employ multi-component Sérsic profiling to provide bulge-disk decompositions for this sample, allowing for the luminosity and stellar mass to be divided between the key structural components: spheroids and disks. Grouping the stellar mass in these structures by the evolutionary mechanisms that formed them, we find that hot-mode collapse, merger or otherwise turbulent mechanisms account for ~46% of the total stellar mass budget, cold-mode gas accretion and splashback mechanisms account for ~48% of the total stellar mass budget and secular evolutionary processes for ~6.5% of the total stellar mass budget in the local (z<0.06) Universe.

Galaxy redshift surveys are powerful probes of cosmology. Yet, in order to fully exploit the information contained in galaxy surveys, we need to improve upon our understanding of the structure formation in the Universe. Galaxies are formed/observed at late times when the density field is no longer linear so that understanding non-linearities is essential. In this thesis, we show that, at high redshifts, we can accurately model the galaxy power spectrum in redshift space by using the standard cosmological perturbation theory. Going beyond the power spectrum, we can use the three-point function, or the bispectrum, to gain important information on the early universe as well as on the galaxy formation via measurements of primordial non-Gaussianity and galaxy bias. We show that the galaxy bispectrum is more sensitive to primordial non-Gaussianities than previously recognized, making high-redshift galaxy surveys a particularly potent probe of the physics of inflation. Weak lensing offers yet another way of probing cosmology. By cross correlating the angular position of galaxies with the shear measurement from galaxy lensing or CMB lensing, we also show that one can obtain the information on cosmological distance scale, the galaxy bias, and the primordial non Gaussianity from weak lensing method. / text

This document consists of two very different projects but the common thread is in the interest of magnetic fields. It describes the effect of magnetic fields in two Interstellar Medium regions in the Galaxy. Electromagnetic force is one of the four fundamental forces in physics. It is not known where magnetic field has initially risen in the Universe, but what is certain is that it has significant effect in the dynamics of star formation and galaxy formation. The studies aim to better understand the effects of field in an active star forming region and in the halo of the Galaxy. We observed the HI 21 cm spectral line via the Zeeman effect in attempt to detect line-of-sight magnetic field strengths in both of the projects. For the star forming region project in Chapter 2, towards the Eagle Nebula, an upper limit of the field strength was determined. From the observational results, physical conditions of the region were modeled. For the second project in Chapter 3, we attempted to detect magnetic fields via Zeeman effect towards non galactic disk objects. All of the observed positions have radial velocities that cannot be explained by the simple galactic rotation. Hence, they are considered to be non galactic disk sources and often grouped as High Velocity Clouds. With a unique observational technique and analysis, we derived the best fit line-of-sight magnetic fields. A particular interest to us is the Smith Cloud. From the detection of magnetic field, we attempted to estimate the density of the ambient medium in the halo, which will be useful for studying the galaxy formation.

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.

General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. First, I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry. I show that the shadow of a black hole as well as the shape of a bright and narrow ring surrounding the shadow depend uniquely on its mass, spin, inclination, and the deviation parameter. I argue that the no-hair theorem can be tested with observations of the supermassive black hole Sgr A*. Second, I investigate the potential of quasi-periodic variability observed in both galactic black holes and active galactic nuclei to test the no-hair theorem in two different scenarios. Third, I show that the profiles of relativistically broadened iron lines emitted from the accretion disks of black holes imprint the signatures of deviations from the Kerr metric. In the second part, I devise a method to test the predicted evaporation of black holes in the Randall-Sundrum model of string theory-inspired braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480. I predict the first detection of orbital evolution in a black-hole binary.

The first chapter begins with the observations of 1,882 sources from the Bolocam Galactic Plane Survey (BGPS) at 1.1 mm in HCO⁺ J = 3 − 2 and N₂H⁺ J = 3 − 2. We determine kinematic distances for 529 sources and derive the size, mass, and average density for this subset of clumps. The median size of BGPS clumps is 0.75 pc with a median mass of 330 M⊙ (assuming T(Dust) = 20 K). The median HCO⁺ linewidth is 2.9 km s⁻¹ indicating the clumps are not thermally supported and provide no evidence for a size-linewidth relationship. This collection of objects is a less-biased sample of star-forming regions in the Milky Way that likely span a wide range of evolutionary states. We study in detail the G111 Infrared Dark Cloud northwest of NGC 7538 with the K-band Focal Plane Array. We map NH₃ (1,1) and (2,2), H₂O maser, and CCS emission simultaneously with the GBT. We find the NH₃ gas traces the 1.1 mm BGPS structure very well with gas kinetic temperatures consistently close to 15 K. Typical column densities are 2.5 × 10¹⁴ cm⁻² with a median abundance of NH₃ to H₂ of 5.94 × 10⁻⁸. The median linewidth of the NH₃ emission is 0.64 km s⁻¹ indicating the filament is not thermally supported. The NH₃ is subthermally populated along the entire filament. Individual NH3 peaks have a median size of 0.61 pc, mass of 188M⊙, and density of 3.4×10³ cm⁻³. An activity analysis shows the most active star forming regions are found at the junctions of the subfilaments that make up the larger G111 IRDC. The last chapter describes our systematic examination of individual student responses to the Light and Spectroscopy Concept Inventory national dataset. We use classical test theory to form a framework of results that is used to evaluate item difficulties, item discriminations, and the overall reliability of the LSCI. We perform an analysis of individual student’s normalized gains, providing further insight into the prior results from this data set. This investigation allows us to better understand the efficacy of using the LSCI to measure student achievement.

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