This work uses multiwavelength observations of nearby galaxies to explore the relationship between star formation and the interstellar medium in galaxies of various sizes and morphology. Galaxies in the Herschel Reference Survey are divided into barred and unbarred spirals to test for differences in dust temperature, dust mass, star formation rate, farinfrared luminosity, NUV-r colour and stellar mass between the two populations. The only significant observed difference is with stellar mass, where barred spirals are generally less massive. I suggest this is due to the speed of bar creation depending on galaxy mass, although this is counter to some previous observations. Trends with Hubble-type and environment are consistent with previous work. The resolved star formation law is studied in the two largest extragalactic sources in the local group, Andromeda (M31) and the Triangulum (M33). The two are measured to have global star formation rates (SFR) of 0.25M⊙ yr−1 and 0.16M⊙ yr−1 respectively using far-ultraviolet and 24 mm emission as star formation tracers. M33 has a higher mean surface density of star formation, as expected as it is later type than M31, and a higher star formation efficiency. Both galaxies appear consistent with the globally averaged SFR and gas surface density of normal spirals studied in previous work, with M31 at the low end in terms of SFR. When looking at smaller scales, both galaxies show evidence of saturation of neutral monatomic hydrogen at §Gas = 10M⊙ pc−2 when looking at the star formation law with total gas. They also appear to follow close to linear star formation laws with molecular gas only, consistent with previous work on resolved galaxies. M31 shows evidence of a sub-linear star formation law with molecular gas, indicating that star formation efficiency is lower in the highest density regions. Testing the relationship in M31 on different pixel scales does not effect the measured Kennicutt-Schmidt index, as has been suggested in previous work. M33 shows a significant portion of the galaxy has a relatively high SFR surface density, but little molecular gas as traced by CO. I suggest this could be evidence of CO-free molecular hydrogen in these regions.

The coalescence of two stellar mass black holes is regarded as one of the most promising sources for the first gravitational-wave (GW) detection with ground-based detectors. The current detection strategies, however, rely on theoretical knowledge of the gravitational waveforms. It is therefore crucial to obtain an accurate and complete description of the GW signal. This thesis concerns the description of precessing black holes. Misalignment between the orbital angular momentum and the spin angular momenta of the two black holes induces precession, leading to complex dynamics that leaves a direct imprint on the GW. Additionally, the evolution of the binary depends on the mass ratio and both spins spanning a sevendimensional intrinsic parameter space. This makes it difficult to obtain a simple, closed-form description of the waveform through inspiral, merger and ringdown. We are therefore interested in 1) developing a conceptually intuitive framework to systematically model precessing waveforms and 2) exploring the possibility of representing the seven-dimensional parameter space by a lower-dimensional subset. First, we introduce an accelerated frame of reference, which allows us to track the precession of the orbital plane. We then analyse the waveforms in this co-precessing frame resulting in an approximate decoupling between the inspiral and precession dynamics. This leads to the important identification of the inspiral rate of a precessing binary with the inspiral rate of an aligned-spin binary. Based on this decoupling, we develop a general framework to construct precessing waveforms by 'twisting up' an aligned-spin waveform with a model for the precession dynamics. In general, precession depends on all seven intrinsic physical parameters, which complicates modelling efforts. However, we find a parameter-reduced representation of the dynamics, which allows us to produce a first closed-form description of the complete waveforms of precessing black-hole binaries within this general and easy-to-grasp framework.

Upon its completion the Herschel ATLAS (H-ATLAS) will be the largest submillimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this thesis, I use a subset of 40 H-ATLAS sources with previously measured redshifts in the range 0.5 < z < 4.2 to derive a suitable average template for high redshift H-ATLAS sources. I find that a template with two dust components (Tc = 23.9 K, Th = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. I use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of ∆z/(1 + z) = 0.26. For sources for which there is prior information that they lie at z > 1 we estimate that the rms of ∆z/(1 + z) = 0.12. I have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 µm selected sources respectively. Using these redshifts I have estimated luminosity functions for the Phase 1 field. This has shown evidence of strong evolution out to a redshift of z ∼ 2. At which point luminosity evolution begins to slow until z ∼ 3, where it appears to stop altogether. Estimations of the angular correlation function showed strong clustering across most wavelengths and redshifts.

This thesis presents an investigation into the effect of environment on a galaxy's ISM. I have used new data from the Herschel Space Observatory, which detects the peak of far-infrared (FIR) emission from cold dust (20 K) in nearby galaxies. Using data from the Herschel Fornax Cluster Survey (HeFoCS) and the Herschel Astrophysical Large Area Terahertz Survey (H-ATLAS) I have measured the FIR fluxes of galaxies in the nearby Fornax cluster and Coma region. In order to measure these FIR fluxes I used the optical shape and size of galaxies as a starting point. In the case of Fornax there was already a high quality optical catalogue, the Fornax Cluster Catalogue (FCC; Ferguson, 1989). However, in the case of the Coma cluster and filament I created my own using data from the SDSS spectroscopic survey, selecting galaxies based on position and velocity. Thus, creating the Coma Cluster Catalogue (CCC) and Coma Filament Catalogue (CFC). For galaxies detected in at least 3 and 5 Herschel bands for the HeFoCS and H-ATLAS galaxies, respectively, I fitted a modified blackbody with a fixed beta emissivity index of 2, yielding dust masses and temperatures for 22 and 198 HeFoCS and H-ATLAS galaxies, respectively. All Early-type galaxies showed a lower mean dust mass and hotter temperature than found for late-types. When comparing early-type galaxies across all sampled environments, their FIR properties are found to be statistically identical. I only find a significant difference in dust-to-stellar mass for late-type galaxies between the filament and a field sample. This may suggest that the effect of the cluster and filament is more subtle than previously thought and that the evolution of the ISM components has mostly taken place well before the cluster was assembled. I use a method to compare multiple parameters for the Coma cluster and filament galaxies and how each is a�ected by local environmental density. Late types show a moderate change in most parameters with the exception of gas-to-stars, which is strongly affected by environmental density. I suggest that late-types' lower sSFRs and higher stellar masses in the cluster when compared to the filament indicate that the galaxies in the cluster formed earlier and are hence more evolved. In order to understand how the baryonic components of the galaxies change as a whole between the cluster and filament I have created mass functions. Using Schechter function fits to stellar, gas and dust mass density ratios for the Coma cluster and filament I calculated the ratio of gas-to-stellar and dust-to-stellar mass densities for each environment finding that Virgo, Fornax, Coma and the filament were gas deficient when compared to the field, but all their dust mass functions appeared identical. This further demonstrates that dust is largely invariant to environment, whereas, gas is affected well before entry into the cluster.

SuperSpec is an innovative, fully planar, compact spectrograph for mm/sub-mm astronomy. Its very small size, wide spectral bandwidth, and highly multiplexed detector readout will enable construction of powerful multi-object spectrometers for observations of galaxies at high redshift. SuperSpec is based on a superconducting filterbank consisting of a series of planar half-wavelength filters to divide up the incoming, broadband radiation. The power in each filter is coupled into a titanium nitride (TiN) lumped element Kinetic Inductance Detector (KID), facilitating the read out of a large number of filter elements with minimal cryogenic electronics. We present electromagnetic simulations of the various components that make up the first generation prototype device. We then present a characterisation of the performance of the TiN detectors and compare these to the standard Mattis-Bardeen prediction. We then demonstrate the operation of the filterbank at 250 GHz through a spectral characterisation made using a Martin-Puplett interferometer measuring a minimum filter bandwidth that corresponds to a spectral resolution of R = 700. From blackbody measurements of the most responsive filter channels, we estimate a system noise equivalent power of 2X10 to power -15 WHz to power -1/2.

We are currently on the brink of the first direct detection of gravitational waves (GWs) with a new generation of GW detectors currently being commissioned. In the period before the advanced detectors come online we must prepare techniques for detector characterisation and advanced data analysis methods to improve our sensitivity to potential sources of GWs. We begin with an outline of GWtheory, derived from Einstein’s general theory of relativity. We introduce each of the main classes of GWsignals, as distinguished by the GW community, focusing mainly on GW bursts. A short outline is also given for compact binary coalescences, continuous waves, and stochastic background. An introduction to GW interferometers is then given, focusing mainly on the GEO600 detector. The stationary noise sources that limit the frequency dependent sensitivity of current GW detectors are discussed: optical readout noise, thermal noise, and seismic noise. We discuss transient noise events (glitches) and the veto methods that are used to remove these events from the GW data channel. Details are given for glitch hunting that was performed at GEO 600 to identify and understand sources of transient noise. We demonstrate a cost-benefit analysis method that could be used for increasing the number of observable sources, by assessing the severity of detector noise sources to efficiently guide commissioning. We introduce X-PI P E L I N E, a coherent search pipeline for GW bursts associated with astrophysical transients such as gamma-ray bursts, and give details of pipeline line development that we were involved in. Results from a search for GW associated with 78 gamma-ray bursts that occurred while only GEO 600 and one of the LIGO or Virgo detectors were taking data are presented; these events have not previously been analysed. The sensitivity of searches for GW bursts is often critically limited by non-Gaussian noise fluctuations that are difficult to distinguish from real signals. We utilised the boosted decision tree multivariate analysis classifier to probe the full space of measured properties of events in an attempt to maximise the power to accurately classify events as signal or background, compared to the standard X-PI P E L I N E. While the LIGO and Virgo detectors are undergoing intense commissioning, GEO600 is the only GW detector taking observations. Therefore, we demonstrate the feasibility of performing a single detector analysis for GW bursts using GEO 600 in preparation for any exceptional astrophysical events (such as a Galactic supernova).

I first perform a statistical analysis on a distribution of pre-stellar core masses. Each core is split into a small number of stars, and two stars are chosen using a prescription based on stellar masses to form a binary system. The rest of the stars are taken to be singles. From this sample of binaries and singles, I compute the stellar initial mass function, the binary frequency and mass ratio distribution as a function of primary mass. I then test if the observed binary frequencies and mass ratios are compatible with this self-similar mapping of cores into stars. I show that self-similar mapping can reproduce the observed binary frequencies and mass ratios well, so long as the efficiency is rather high (100%), and each core fragments into about 4 or 5 stars. Using the code Seren view, I then perform N-body simulations with core-clusters. I investigate the formation of multiple systems, and qualify the dependence of their parameters and longevity on certain initial conditions, including (i) the number of stars in a core-cluster, (ii) the variance of masses in those stars, (iii) the virial ratio and (iv) radial dependence of stellar density. I expand on those results by including (a) a prescription for the influence of disks during stellar ybys, (b) different initial spatial configurations of the stars (i.e. line and ring clusters) and (c) a background potential due to residual gas in the core-cluster. The full range of periods observed in the field cannot be explained by the distribution of periods of pure binaries alone, which is too narrow. However, the wide range can be explained either by combining the periods of pair-wise orbits of all multiple systems, i.e. the widest periods observed are in fact pair-wise orbits of higher-order multiples with unresolved companions, or by considering a distribution of pre-stellar cores that have a range of virial ratios.

This thesis is broadly concerned with the dynamics, statistics and phenomenology of the perturbed Universe. By studying the perturbations to cosmological spacetimes, and the subsequent growth of large scale structure, we find that we can link both fundamentally and astrophysically interesting physics to cosmological observables. We use a healthy mix of statistical, analytical and numerical techniques throughout this thesis. In Chapter 2 we introduce and summarise the statistics of random fields, as these are fundamental objects used to model cosmological observables. We introduce the spherical Fourier-Bessel expansion as a tool to perform genuine 3-dimensional studies of cosmological random fields. In Chapter 3 we introduce the theory of inflation and discuss the basic machinery that allows us to calculate the statistical properties of the quantum mechanical flucatuations that seed large scale structure. What we see is that different fundamental physics in the early Universe leads to different statistical properties that we may test. The second half of Chapter 3 introduces the large scale structure of the Universe that describes the clustering of galaxies on cosmological scales. We discuss the growth and evolution of structure under gravitational collapse and the core observables that are predicted, such as the power spectrum, variance and skewness. Chapter 4 introduces the Minkowski functionals. These are a set of topological statistics that probe the morphological properties of random fields. In particular they may be used to quantify deviations from Gaussianity in the large scale structure of galaxies. The deviations from Gaussianity can be generated by two primary mechanisms: 1) The gravitational collapse of perturbations is a non-linear process. Even if we have Gaussian initial conditions, gravitational collapse will induce non-Gaussianity. 2) Different theories for the early Universe will imprint different non- Gaussian features in the primordial perturbations that seed large scale structure, i.e. we have non-Gaussian initial conditions. We can connect the amplitude and momentum dependence of the non-Gaussianity to different fundamental interactions. We introduce a topological statistic based on the Minkowski functionals that retains the momentum dependence giving us greater distinguishing power between different contributions to non-Gaussianity. In Chapter 5 we introduce the Baryon Acoustic Oscillations (BAOs) as described in the spherical Fourier-Bessel formalism. The BAOs are a solid prediction in cosmology and should help us to constrain cosmological parameters. We implement a full 3-dimensional study and study how redshift space distortions, induced by the motion of galaxies, and non-linearities, induced by gravitational collapse, impact the characteristics of these BAOs. Chapter 6 extends the spherical Fourier-Bessel theme by introducing the thermal Sunyaev- Zel’dovich (tSZ) effect and cosmological weak lensing (WL). It is thought that weak lensing will provide an unbiased probe of the dark Universe and that the tSZ effect will probe the thermal history of the Universe. Unfortunately, the tSZ effect loses redshift information as it is a line of sight projection. We study the cross-correlation of the tSZ effect with WL in order to reconstruct the tSZ effect in a full 3-dimensional study in an attmept to recover the lost distance information. We use the halo model, spectroscopic redshift surveys and suvery effects to understand how detailed modelling effects the tSZ-WL cross correlation. Chapter 7 marks a real change in theme and introduces the subject of relativistic cosmology. Inparticular we introduce the 1+3, 1+1+2 and 2+2 formalisms as tools to study cosmological perturbations. We provide rather self-contained introductions and provide some minor corrections to the literature in the 1+1+2 formalism as well as introducing new results. In Chapter 8 we apply the 1+1+2 and 2+2 approaches to the Schwarzschild spacetime. Here we outline the full system of equations in both approaches and how they are related, setting up a correspondence between the two. Our aim is to construct closed, covariant, gauge-invariant and frame-invariant wave equations that govern the gravitational perturbations of the Schwarzschild spacetime. We correct a result in the literature and derive two new equations. The first governs axial gravitational perturbations and is related to the magnetic Weyl scalar. The second is valid for both polar and axial perturbations and is given by a combination of the magnetic and electric Weyl 2-tensors. We discuss their relation to the literature at large. Finally, in Chapter 9 we apply the 1+1+2 and 2+2 approaches the LTB spacetime. This inhomogeneous but spherically symmetric spacetime is the first stepping stone into genuinely inhomogeneous cosmological spacetimes. We seek a closed, covariant master equation for the gravitational perturbations of the LTB spacetime. We present an equation governing axial gravitational perturbations and a preliminary equation, valid for both the polar and axial sectors, that is constructed from the electric and magneticWeyl 2-tensors but is coupled to the energy-momentum content of the LTB spacetime. We discuss how auxilliary equations may be introduced in order to close the master equation for polar and axial perturbations. This last result leads to the identification of H as a master variable for axial perturbations of all vacuum LRS-II spacetimes and the LTB spacetime. It is thought that these results can be extended to non-vacuum LRS-II spacetimes. Likewise, the master variable constructed from Weyl variables constitutes a master variable for all vacuum LRS-II spacetimes and it is thought that this will extend to the non-vacuum case.

So far the progenitors of short γ-ray bursts (SGRBs) have proved elusive. Their presence within both old and young environments and their bias against starforming regions provide tantalising evidence of a neutron star binary or neutron star - black hole merger origin. Within this thesis we study an array of characteristics of the population of SGRBs focussing in particular on their host environments and afterglow properties in the optical and X-ray bands. In particular we consider a set of SGRBs with no detectable host galaxy to deep limits and no clear host in the field from probabilistic arguments. These GRBs either represent a population at high redshift or with high offsets from low redshift hosts. Comparing the offsets of these GRBs from their potential hosts with random positions on the sky we find they are somewhat closer than expected, suggesting these GRBs are more likely to have been kicked from relatively local hosts. We also consider the issue of classification, given suggestions that the often used two second duration divide for SGRBs may produce a sample with a high contamination from collapsar objects or potentially a suggested third class of intermediate objects. We look at a sample of optically-detected SGRBs below the nominal two second divide and go on to consider properties of a larger sample of GRBs comparing varying duration bins. From constructed optical lightcurves and SEDs, we constrain the presence of extinction, jet breaks, supernovae and kilonovae. Though there is a suggestion that such a sample would be 40% contaminated from collapsar objects we find, from supernova constraints combined with duration and spectral hardness fits from Bromberg et al. (2013) that only 22% of objects in our sample could have been collapsars. The optical constraints placed on a kilonova (an r-process transient associated with neutron star mergers), suggest this transient is fainter than has sometimes been predicted but is consistent when considering additional opacities from the rprocess material which could cause strong reddening to the infra-red. Finally, we do not find evidence for a distinct class of intermediate GRBs, though there are likely additional progenitors which create GRB-like objects. At the intermediate duration we do find two unusual individual events not typical of LGRBs: GRBs 100816A and 060505. We find that GRB100816A is most likely a mis-classified SGRB, from its position within its host and the constraint on any associated supernova.

Multi-wavelength astronomical surveys have revolutionised the field. They have dramatically changed the way we search for sources, as well as the way we analyse their data. In this thesis, we focus on the search for compact objects using different photometric surveys, from X-rays to near-infrared, including the optical bands. Compact sources are the end points of stellar evolution. They consist of white dwarfs, neutron stars and black holes. This thesis consists of two key parts. The first concerns the exploitation of three near-infrared surveys of the Galactic Bulge in order to find the counterparts of 1658 X-ray sources detected with NASA’s Chandra satellite. These sources are the focus of the Galactic Bulge Survey (GBS), which has a main goal to find low-mass X-ray binaries, composed of neutron stars or stellar-mass black holes accreting material from a low-mass companion. We present all viable counterpart candidates and associate a false alarm probability (FAP) to each near-infrared match in order to identify the most likely counterparts. The FAP takes into account a statistical study involving a chance alignment test, as well as considering the positional accuracy of the individual X-ray sources. We find that although the star density in the Bulge is very high, ∼90% of our sources have a FAP < 10%, indicating that for most X-ray sources, viable near-infrared counterparts candidates can be identified. In addition to the FAP, we provide positional and photometric information for candidate counterparts to ∼95% of the GBS X-ray sources. This information in combination with optical photometry, spectroscopy and variability constraints will be crucial to characterize and classify secure counterparts. We also present the available GBS optical photometry, near-infrared as well as optical variability data, and some initial spectroscopic results. In the second part, we search for white dwarfs in a region of the sky known as the Kepler field. The Kepler mission provides superior time series photometry of a 116 deg2 field. In order to search for white dwarfs, we carried out our own survey, the Kepler- INT Survey (KIS), using the U, g, r, i and Hα filters, reaching down to ∼ 20th mag. Our second data release catalogue contained ∼14.5 million sources and covered ∼97% of the field. Using KIS, we selected white dwarf candidates on the basis of their colours, which were then confirmed via optical spectroscopy. We discovered 43 new white dwarfs, including six pulsating hydrogen-atmosphere white dwarfs. Asteroseismology is the only way to probe the interiors of the stars thus finding more pulsators is crucial. We obtained short-cadence Kepler observations of four of our pulsating white dwarfs: KIC11911480, KIC10132702, KIC0435037 and KIC07594781. All four have pulsation periods within the expected range for this type of variable white dwarfs. They also all confirm that white dwarfs are slow rotators, with rotation periods in the order of days. We end this Thesis with the full asteroseismic analysis of KIC11911480, our first ZZCeti in the Kepler field.