A new method for generating initial data for simulations of neutron stars in binary systems. The construction of physically relevant initial data is crucial to accurate assessment of gravitational wave signals relative to theoretical predictions. This method builds upon the Bowen-York curvature for puncture black holes. This data is evolved and compared against simulations in the literature with respect to orbital eccentricity, merger and collapse times, and emitted energy and angular momentum. The data exhibits some defects, including large central density oscillations in stars and center of mass drift in unequal-mass systems. Some approaches for improvements in potential future work are discussed.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

This thesis will present a new cosmic shear analysis pipeline SUNGLASS (Simulated UNiverses for Gravitational Lensing Analysis and Shear Surveys). SUNGLASS is a pipeline that rapidly generates simulated universes for weak lensing and cosmic shear analysis. The pipeline forms suites of cosmological N-body simulations and performs tomographic cosmic shear analysis using a novel line-of-sight integration through the simulations while saving the particle lightcone information. Galaxy shear and convergence catalogues with realistic 3-D galaxy redshift distributions are produced for the purposes of testing weak lensing analysis techniques and generating covariance matrices for data analysis and cosmological parameter estimation. This thesis presents a suite of fast medium-resolution simulations with shear and convergence maps for a generic 100 square degree survey out to a redshift of z = 1.5, with angular power spectra agreeing with the theoretical expectations to better than a few percent accuracy up to ℓ = 103 for all source redshifts up to z = 1.5 and wavenumbers up to ℓ = 2000 for source redshifts z ≥ 1.1. A two-parameter Gaussian likelihood analysis of Ωm and σ8 is also performed on the suite of simulations for a 2-D weak lensing survey, demonstrating that the cosmological parameters are recovered from the simulations and the covariance matrices are stable for data analysis, with negligible bias. An investigation into the accuracy of traditional Fisher matrix calculations is presented. Fisher Information Matrix methods are commonly used in cosmology to estimate the accuracy that cosmological parameters can be measured with a given experiment, and to optimise the design of experiments. However, the standard approach usually assumes both data and parameter estimates are Gaussian-distributed. Further, for survey forecasts and optimisation it is usually assumed the power-spectra covariance matrix is diagonal in Fourier-space. But in the low-redshift Universe, non-linear mode-coupling will tend to correlate small-scale power, moving information from lower to higher-order moments of the field. This movement of information will change the predictions of cosmological parameter accuracy. In this thesis, the loss of information is quantified by comparing näıve Gaussian Fisher matrix forecasts with a Maximum Likelihood parameter estimation analysis of the suite of mock weak lensing catalogues derived from the SUNGLASS pipeline, for 2-D and tomographic shear analyses of a Euclid-like survey. In both cases the 68% confidence area of the Ωm − σ8 plane is found to increase by a factor 5. However, the marginal errors increase by just 20 to 40%. A new method is proposed to model the effects of non-linear shear-power mode-coupling in the Fisher Matrix by approximating the shear-power distribution as a multivariate Gaussian with a covariance matrix derived from the mock weak lensing survey. The findings in this thesis show that this approximation can reproduce the 68% confidence regions of the full Maximum Likelihood analysis in the Ωm − σ8 plane to high accuracy for both 2-D and tomographic weak lensing surveys. Finally, three multi-parameter analyses of (Ωm, σ8, ns), (Ωm, σ8, ns, ΩΛ)and (Ωm, σ8, h, ns, w0, wa) are performed to compare the Gaussian and non-linear mode-coupled Fisher matrix contours. The multi-parameter volumes of the 1σ error contours for the six-parameter non-linear Fisher analysis are consistently larger than for the Gaussian case, and the shape of the 68% confidence volume is modified. These results strongly suggest that future Fisher Matrix estimates of cosmological parameter accuracies should include mode-coupling effects.

ter have most of their energy held in the region of the water column near to the surface. Tsunamis are extremely long waves with long periods that can range from five minutes to several hours. Due to their very long wavelengths, tsunamis travel at the shallow water wave celerity which is equal to the square root of the gravitational acceleration times the water depth. The speed of a tsunami in the open ocean can reach in excess of 500 miles per hour. Tsunamis are also characterized by low wave height when moving through oceanic depths and are often hard to recognize when seen out in the deep ocean. As tsunamis approach the coastal region, they are affected by the rapid decrease in water depth. / US Navy (USN) author.

We perform a measurement of the mass-richness relation of the redMaPPer galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky Survey (SDSS). We have carefully characterized a broad range of systematic uncertainties, including shear calibration errors, photo-z biases, dilution by member galaxies, source obscuration, magnification bias, incorrect assumptions about cluster mass profiles, cluster centring, halo triaxiality and projection effects. We also compare measurements of the lensing signal from two independently produced shear and photometric redshift catalogues to characterize systematic errors in the lensing signal itself. Using a sample of 5570 clusters from 0.1 <= z <= 0.33, the normalization of our power-law mass versus. relation is log(10)[M-200m/ h-M-1(circle dot)] = 14.344 +/- 0.021 (statistical) +/- 0.023 (systematic) at a richness lambda= 40, a 7 per cent calibration uncertainty, with a power-law index of 1.33(- 0.10)(+0.09) (1 sigma). The detailed systematics characterization in this work renders it the definitive weak lensing mass calibration for SDSS redMaPPer clusters at this time.

Cosmological constraints from galaxy surveys are as accurate as our understanding of the relative distributions of dark matter and galaxies, known as galaxy bias. Weak gravitational lensing is a powerful probe of galaxy bias, since the distortion in the shapes of distant galaxies, called shear, is directly related to the dark matter distribution, which can be compared to the galaxy field. I look at the galaxy clustering amplitude relative to the dark matter field, quantified by the galaxy bias b, as well as the cross-correlation coefficient r, which tells us how correlated the positions of galaxies are with the dark matter. In this thesis I present several techniques to constrain galaxy bias through weak lensing, using both numerical simulations and observational data. The most commonly used method, using aperture statistics, is shown to be subject to serious systematics in the presence of noisy data and scale- and time dependence in the galaxy bias. A local comparison technique is introduced, where the foreground distribution is used to predict the shear in the background, to which it is compared. The technique is tested with simulations, concluding that it requires high quality data. A model fitting approach is proposed, based on the McDonald (2006) galaxy bias model. The two parameters of this model, a large scale bias, b1, and a parameter, b2, that quantifies the scale dependence of the bias, are insufficient in the presence of stochasticity. Therefore, R is introduced as an additional parameter to take this into account. I present galaxy bias constraints for two spectroscopic galaxy samples: the Baryon Oscillations Spectroscopic Survey (BOSS) and the WiggleZ Dark Energy Survey (WiggleZ), applying the traditional aperture method and the model fitting approach to the Red Sequence Cluster Lensing Survey (RCSLenS). Both techniques strongly suggest that galaxies trace mass, but in a complicated way, with differences in scale- and time dependence between the samples considered. The WiggleZ galaxy bias is found to be around b ~ 1:2, depending on redshift and scale, and has a low cross-correlation coefficient of r ~ 0:5 at small scales. The BOSS samples have higher bias with scale dependence around b ~ 2:0 and show no sign of stochasticity, finding r to be close enough to unity to be explained within a deterministic scenario. The observations are in line with previous galaxy bias measurements from lensing data. The thesis incorporates work on the X-ray Luminosity Function (XLF) of galaxy clusters, measured from the Wide Angle ROSAT Pointed Survey (WARPS). Evolution is quantified with a likelihood analysis and I conclude that it is driven by a decreasing number density of high luminosity clusters with redshift, while the bulk of the cluster population remains nearly unchanged out to redshift z ~ 1:1, as expected in a low density Universe. I conclude by investigating the impact of my galaxy bias measurements from BOSS and WiggleZ on the growth rate of structure, as extracted from Redshift Space Distortions (RSD). The imperfect correlation between the galaxy and matter field, as quantified by R and b2, leads to an underestimation of the true growth rate under the assumption of a linear bias. Therefore, in order to constrain galaxy bias and gravity simultaneously, future cosmological redshift surveys require high quality lensing data.

With a large, unique spectroscopic survey in the fields of 28 galaxy-scale strong gravitational lenses, we identify groups of galaxies in the 26 adequately sampled fields. Using a group-finding algorithm, we find 210 groups with at least 5 member galaxies; the median number of members is 8. Our sample spans redshifts of 0.04 <= z(grp) <= 0.76 with a median of 0.31, including 174 groups with 0.1 < z(grp) < 0.6 The groups have radial velocity dispersions of 60 <= sigma(grp) <= 1200 km s(-1) with a median of 350 km s(-1). We also discover a supergroup in field B0712+472 at z = 0.29 that consists of three main groups. We recover groups similar to similar to 85% of those previously reported in these fields within our redshift range of sensitivity and find 187 new groups with at least five members. The properties of our group catalog, specifically, (1) the distribution of sgrp, (2) the fraction of all sample galaxies that are group members, and (3) the fraction of groups with significant substructure, are consistent with those for other catalogs. The distribution of group virial masses agrees well with theoretical expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434, B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716, MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723) are members of groups with at least five galaxies, and one more (B0712+472) belongs to an additional, visually identified group candidate. There are groups not associated with the lens that still are likely to affect the lens model; in six of 25 (24%) fields (excluding the supergroup), there is at least one massive (sigma(grp) >= 500 km s(-1)) group or group candidate projected within 2' of the lens.

A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of Science School of Computational and Applied Mathematics. May 2015. / In this thesis we present numerical simulations of the gravitational collapse of isothermal clouds of one solar mass at a temperature of 10K. We will consider two types of initial conditions – initially uniform spheres and perturbed Bonnor-Ebert spheres. The aim of the performed numerical simulations is to investigate the core bounce described by Hayashi and Nakano [1]. They reported that if strong enough, the shock wave would be capable of ionizing the gas in the collapsing cloud. The simulations are performed using two numerical methods: the TVD MUSCL scheme of van Leer using a Roe flux on a uniform grid and the TVD Runge-Kutta time-stepping using a Marquina flux on a non-uniform grid. These two particular methods are used because of their differences in numerical structure. Which allows us to confidently make statements about the nature of the collapse, particularly with regards to the core bounce. The convergence properties of the two methods are investigated to validate the solutions obtained from the simulations. The numerical simulations have been performed only in the isothermal regime by using the Truelove criterion [2] to terminate the simulation before central densities become large enough to cause artificial fragmentation. In addition to the numerical simulations presented in this thesis, we also introduce new, analytical solutions for the steady-state accretion of an isothermal gas onto a spherical core as well as infinite cylinders and sheets. We present the solutions and their properties in terms of the Lambert function with two parameters, γ and m. In the case of spherical accretion we show that the solution for the velocity perfectly matched the solutions of Bondi [3]. We also show that the analytical solutions for the density – in the spherical case – match the numerical solutions obtained from the simulations. From the agreement of these solutions we propose that the analytical solution can provide information about the protostellar core (in the early stages of its formation) such as the mass.

The first direct detection of gravitational waves in 2015, and the multiple detections that followed ushered in the era of gravitational-wave astronomy. With these developments, the focus of the gravitational-wave community shifted from detection to precision measurement, requiring a factor of ten improvement in calibration accuracy to maximize the astrophysical information that can be extracted from these detected signals. This dissertation discusses the implementation and characterization of a radiation-pressure-based calibration system called the Photon calibrator that is used as the primary calibration reference for the Advanced LIGO detectors. It also discusses the techniques and procedures used to realize sub-percent accuracy calibration of absolute displacement fiducials introduced using the Photon calibrator system during Advanced LIGO’s first and second observing runs. Using the Photon calibrator systems, frequency dependent calibration of the interferometer responses was achieved at the level of 2-3% in magnitude and 3- 5 degrees in phase across the LIGO detection band. This level of calibration accuracy has already played a significant role in extracting astrophysical parameters from LIGO’s detections. With the LIGO and Virgo detectors operating at design sensitivity, updated rate estimates indicate that measurement of the Hubble constant with gravitational waves with 1% accuracy will be possible within the next decade. This will require absolute amplitude calibration of the detectors at the sub-1% level. This dissertation also discusses the improvements that have been implemented in the Photon calibrator systems that will reduce the uncertainty in absolute displacement to below 0.5%. The gravitational waves from the post-merger phase of binary neutron stars are expected to contain interesting features at frequencies up to few kHz, carrying rich information about neutron-star astrophysics. This dissertation discusses the calibration errors introduced by test mass deformations caused by calibration forces at frequencies above 1 kHz. The errors, estimated using Finite Element Analysis, is in reasonable agreement with measurement results in the 1 to 5 kHz band. These investigations have enabled the reduction of calibration uncertainty at these frequencies, which should enhance our ability to decipher the neutron star astrophysics encoded in the gravitational wave signals from the post-merger phase. This dissertation includes previously published co-authored material.