The M–σ relations observed between the masses of central massive objects (CMOs: either a nuclear star cluster or a supermassive black hole) in galaxy nuclei and the stellar velocity dispersion of their host galaxy bulges strongly suggest that the evolution of CMOs and their host galaxies are closely related. Self-regulated feedback from CMOs sweeps the surrounding ambient medium into a shell and when the CMO is at a critical mass the shell is driven from the galaxy, cutting off fuel to the CMO for further growth and locking in the M–σ relations. We investigate the M–σ relations that result from either momentum- or energy-conserving feedback. In the case of momentum-conserving feedback in an isothermal halo, we find the previously derived critical mass is not by itself sufficient to drive the shell to large radius and it takes a CMO with a mass three times the critical value to drive the shell to the escape speed of the halo. In non-isothermal haloes both of these issues are mitigated as the critical mass is sufficient to drive any shell to large radius where it will accelerate and escape the halo. For energy-conserving feedback, we focus on the case that the CMO is a black hole and we find Mvw ∝ σ5, where vw is the black hole wind speed. This relation allows us to infer the wind speeds a sample of now quiescent galaxies would have had during an active phase, and we find good agreement with distributions of observed wind speeds in local active galaxies. We discuss the possibility of a transition from momentum- to energy-driving, the implications of relaxing the assumption of steady CMO winds and the effects these may have on the derived M–σ relations.

The detection of dark matter (DM) by direct detection experiments has great potential to shed light on particle physics beyond the Standard Model. However, uncertainties in the DM speed distribution f1(v) may lead to biased reconstructions of particle physics parameters, such as the DM mass and interaction cross sections. In this work, we aim to determine whether these parameters can be determined from future direct detection data without any prior assumptions about f1(v). We study previous methods for parametrising f1(v) and show that they may still lead to biased reconstructions of the DM parameters. We propose an alternative smooth, general parametrisation, which involves writing the logarithm of the speed distribution as a polynomial in v. We test this method using future direct detection mock data sets and show that it allows an unbiased reconstruction of the DM mass over a range of particle physics and astrophysics parameters. However, the unknown fraction of DM particles with speeds below the energy thresholds of the experiments means that only a lower bound can be placed on the interaction cross sections. By introducing data from neutrino telescope experiments, such as IceCube, this degeneracy in the cross section can be broken, as these experiments probe the low speed DM population. Combined with our parametrisation method, this allows a robust reconstruction of the DM mass and cross sections without relying on any assumptions about the DM speed distribution. The function f1(v) itself can also be reconstructed, allowing us to probe the distribution function of the Milky Way. Finally, we propose a method of extending this parametrisation to directional data, which should allow even more information to be extracted from future experiments without the need for astrophysical assumptions.

Since Lick indices were introduced in 1994, they have been used as a source of observational data against which computer models of galaxy evolution have been compared. However, as this thesis demonstrates, observed Lick indices lead to mathematical ill-conditioning: small variations in observations can lead to very large differences in population synthesis models attempting to recreate the observed values. As such, limited reliance should be placed on any results currently or historically in the literature purporting to give the star formation history of a galaxy, or group of galaxies, where this is deduced from Lick observations taken from a single instrument, without separate verification from at least one other source. Within these limitations, this thesis also constrains the star formation histories of 21 nearby elliptical galaxies, finding that they formed 13.26 +0.09 -0.06 Gyrs ago, that all mergers are dry, and that galactic winds are formed from AGN activity (rather than being supernovae-driven). This thesis also finds evidence to support the established galaxy-formation theory of “downsizing”. An existing galactic model from the literature is examined and evaluated, and the reasons for it being unable to establish star formation histories of individual galaxies are ascertained. A brand-new model is designed, developed, tested and used with two separate data sets, corroborated for 10 galaxies by data from a third source, and compared to results from a Single Stellar Population model from the literature, to model the star formation histories of nearby elliptical galaxies.

Observations of astrophysical systems in different wavelengths can reveal insights in to systems which are not available from a single wavelength. The same can be expected from multi-channel observations of systems which also produce gravitational waves (GWs). The most likely source of strong, detectable GWs, which will also produce an electromagnetic (EM) signature, is the merger of compact objects containing neutron stars (NS) and black holes (BH), namely NS-NS and NS-BH systems. The focus of this thesis is to summarise current and past efforts to detect an EM counterpart of a GW event, with emphasis on compact merger sources. To begin, the formulation of GWs in general relativity is brie y discussed, as well as the main classes of GW sources. The global networks of GW interferometers in the recent past and near future are described, together with brief explanations of operational principles and the main challenges GW detectors face to make a confident detection. Current literature is reviewed to give a brief summary of the most promising sources which produce both GW and EM signals. Emphasis is given to gamma-ray bursts (GRBs), their afterglows, and kilonovae. In addition a brief description of GW searches triggered by an external source (such as a GRB) is given. A new form of search is then discussed in which GW events are used to point conventional EM telescopes, with emphasis on rapidly slewing, wide field of view optical telescopes. The main challenge in this form of search is that timing information from a network of GW interferometers yields large error regions for the source sky direction making it diffcult to locate an EM transient. Therefore a new statistic is presented in which galaxies (taken from a galaxy catalogue) within this search region are ranked. The probability of identifying the host galaxy of a GW signal from NS-NS and NS-BH systems is investigated and results presented for past and future GW detector configurations. The ROTSE-III telescope system took part in this first search for EM counterparts of GW triggers. With four identical robotic telescopes located across the world it responded to five GW events. Presented is an automation of the ROTSE image processing pipeline which allows large-scale processing and automated validation and classification of candidates. A background study was conducted to better understand the optical transient background and to determine the statistical significance of candidates. Pipeline performance is tested by inserting simulated transients following kilonova and GRB lightcurves in to images; an efficiency study is described. Finally the results of the images taken in response to the five GW events are presented and discussed.

Theory predicts that a large fraction of CVs should have passed through the minimum period. The Sloan Digital Sky Survey (sdss) sample is finally unearthing these systems in large numbers. But due to their faint donor stars, the orbital period is often the only measurable system parameter for most CVs. The indirect measurable of the superhump period, and hence superhump excess, could potentially provide an indication of the mass ratio of the systems via the empirical relation between the two observables. While this relation is potentially very useful for the determination of mass ratios, the large scatter in the calibrators, especially at the low mass ratio end, prohibits a direct conversion between easy to measure light curve variability and the much sought after mass ratio. To place a short period CV firmly on the evolutionary track (e.g pre- or post bounce systems), more direct methods to determine the mass ratio are required, as well as a better calibration and validation of the relation between the superhump excess and mass ratio. We can achieve this, by constraining the mass ratios of short period CVs using dynamical constraints on the radial velocities of the binary components. The radial velocity of the WD (K1) is only occasionally directly measurable as the WD features are typically swamped by the strong disc features. As the disc is centred on the WD, measuring the disc radial velocity can give an indication of the WD radial velocity, but these measures tend to be biased by hotspots and other asymmetries in the disc. Measuring the radial velocity of the donor star (K2) is less straightforward and normally performed by either measuring the radial velocity of the donor absorption lines for earlier type donor stars, or via emission lines associated with the donor star, if irradiated by the disc and WD. The first method fails in short period CVs as the faint features from the late type donors in these systems are concealed in the accretion and WD dominated optical spectrum, even at very low mass loss rates. The second method comes with tight timing constraints as the irradiated donor is generally only visible on top of the double peaked disc emission shortly after outburst and data needs to be obtained via target of opportunity programs. In this thesis, we present a spectroscopic survey of short periods CVs and explore new techniques in addition to the traditional methods for the determination of the radial velocity components. We combine these new methods with the exploitation of the more `exotic' Ca ii triplet lines in the I-band in addition to the commonly used Balmer lines. We will show that, while it suffers from some of the same systematics as the Balmer lines, we can measure K1 better in Ca ii than in Balmer, especially when exploiting Doppler maps for these measures. More importantly for many systems, donor emission is visible in the Ca ii lines, which provides us with measures for the radial velocity amplitude of this feature (Kem). These, combined with K-correction models, yield a good measure of K2. We find that the determination of Kem is easy in Doppler maps, and that the K-correction, via irradiation methods, is fairly solid. We use these values to dynamically constrain the mass ratios for 13 CVs, including several eclipsing systems to test the validity of our method. The survey includes well known systems such as GW Lib, WZ Sge, OY Car and IP Peg.

The AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultrashort period, mass-transferring white dwarf binaries, some of which may be Type Ia supernova progenitors. These systems represent the end product of several finely-tuned evolutionary pathways, and as such are of great interest for binary stellar evolution theory. They are also some of the strongest known sources of low-frequency gravitational waves. Establishing their space density is important for constraining evolutionary models, and the signals we expect to detect from the Galactic population. This has been difficult as much of the known population has been discovered in a heterogeneous manner. In this thesis I present the latest results from a spectroscopic survey designed to uncover the hidden population of AM CVn binaries in the photometric database of the Sloan Digital Sky Survey (SDSS). This small, colour-selected sample of ∼2000 candidates, is expected to contain the majority of all AM CVn binaries in the SDSS. The survey is now approximately 70 per cent complete, and the discovery of only seven new AM CVn binaries indicates a lower space density than previously predicted. Characterisation of the sample requires detailed follow-up observations after the initial discovery, in order to determine the orbital period. I present time-resolved spectroscopy of the recently-discovered AM CVn binary SDSS J173047.59+554518.5, and the dwarf nova SBSS 1108+574. The orbital period I measure for SDSS J1730 confirms its ultracompact binary nature. The quiescent spectrum of SBSS 1108+574 is unusually rich in helium compared to typical cataclysmic variables (CVs). I find that its orbital period is significantly below the normal CV period minimum. This indicates that the donor in SBSS 1108+574 is highly evolved, making it a candidate for the often-dismissed ‘evolved CV’ channel for AM CVn binary formation. I discuss a wider search for new AM CVns in the SDSS spectroscopic database, and present two new systems discovered in SDSS-III spectroscopy. Since this search has revealed only these two new systems, it is unlikely that we have missed a large population of AM CVn binaries, and their discovery should have little effect on our previous calculations of the AM CVn space density.

Large scale digital sky surveys have produced an unprecedented volume of uniform data covering both vast proportions of the sky and a wide range of wavelength, from the ultraviolet to the near-infrared. The challenge facing astronomers today is how to use this multitude of information to extract trends, outliers and and rare objects. For example, a large sample of single white dwarf stars has the potential to probe the Galaxy through the luminosity function. The aim of this work was to study stellar and planetary remnants in these surveys. In the last few decades, it has been shown that a handful of white dwarfs have remnants of planetary systems around them, in the form of a dusty disc. These are currently providing the best constraints on the composition of extra-solar planetary systems. Finding significant numbers of dusty discs is only possible in large scale digital sky surveys. I ultilised the SDSS DR7 and colour-colour diagrams to and DA white dwarfs from optical photometry. This nearly doubled the number of spectroscopically con- armed DA white dwarfs in the SDSS compared with DR4 [Eisenstein et al., 2006], and introduced nearly 10; 000 photometric-only DA white dwarf candidates. I further cross-matched our white dwarf catalogue with UKIDSS LAS DR8 to carry out the currently largest and deepest untargeted search for low-mass companions to, and dust discs around, DA white dwarfs. Simultaneously, I analyzed Spitzer observations of 15 white dwarfs with metal-polluted atmospheres, all but one having helium-dominated atmospheres. Three of these stars were found to have an infrared excess consistent with a dusty disc. I used the total sample to estimate a typical disc lifetime of log[tdisc(yr)] = 5:6+1:1, which is compatible with the relatively large range estimated from different theoretical models. Subdwarf population synthesis models predicted a vast population of subdwarfs with F to K-type companions, produced in the effcient RLOF formation channel. I used a cross-match of ultraviolet, optical and infrared surveys to search for this unseen population. I select a complementary sample to those found from radial velocity surveys, offering direct tests of binary evolution pathways. Finally, I present a method to use common proper motion white dwarf pairs to constrain the initial-final mass relation, which is extremely uncertain at low masses. In the example I show, one of the stars is a magnetic white dwarf with B ' 6 MG, making this a rare and intriguing system from a magnetic white dwarf formation point of view.

Gravitational waves, predicted by the theory of General Relativity, are fluctuations in the curvature of space-time which arise from the asymmetric acceleration of mass. While gravitational waves have yet to be detected directly, measurements of the inspiral rate of a binary pulsar system have provided strong evidence for their existence and a world-wide effort to develop more sensitive detectors is ongoing. In addition to testing predictions of General Relativity, observation and analysis of gravitational waves from astrophysical sources will provide new insights into a wide range of phenomena including black holes, neutron stars and supernovae. Gravitational waves are quadruple in nature, and therefore produce fluctuating tidal strains on space. Long baseline gravitational wave detectors aim to measure this effect using laser interferometry to measure fluctuations in the relative separation of free masses, coated to form highly reflective mirrors and suspended as pendulums at the ends of perpindicular arms up to 4 km in length. There are currently several long baseline gravitational wave detectors in operation around the world, including the three LIGO detectors in the US, the UK/German GEO600 detector near Hannover and the French/Italian Virgo detector near Pisa. The strain expected from gravitational waves is very small, of order [~10-[superscript 22. The magnitude of the resultant displacement is such that the thermal motion of the mirrors and their suspensions forms an important limit to detector sensitivity. The level of thermal noise is related to the mechanical dissipation of the materials used in the test mass and the mirror coatings.

Methods for searching for periodic gravitational wave signals from triaxial pulsars using interferometric gravitational wave detectors have been developed. Since the gravitational wave signals from pulsars are expected to be weak, long stretches of data must be used for any detection. Over the course of a day, and a year, these periodic signals are Doppler shifted due to the motion of the Earth. The response of the interferometers to each polarisation of gravitational waves will also give rise to an amplitude modulation of the periodic signal. These effects are taken into account and an end-to-end Bayesian scheme for making inferences from the data is presented. Several software tests have been performed to validate the core routines, such as barycentring, using independent software. The GEO 600 and LIGO interferometers had their first scientific data run (S1) for 17 days between 23 August and 9 September 2002. An analysis was carried out to search for gravitational wave signals from pulsar B1937+21. While no signals were detected, a 95% upper limit of h0 < 1.4 x 10-22 was determined using S1 data where h0 is the amplitude of the gravitational waves. Given that pulsar B1937+21 is at a distance of 3.6 kpc, and assuming a moment of inertia of 1038kg m2, the corresponding upper limit on the equatorial ellipticity was determined to be = 2.9 x 10-4. The upper limit on gravitational waves from pulsar B1937+21 using S1 data was over an order of magnitude lower than the previous best limit at the time. Data from LIGO's second science run (S2) in the spring of 2003 was analysed with the sensitivity of each detector in the network being roughly an order of magnitude better than in S1 across a large range of frequencies. Upper limits were placed on a total of 28 isolated pulsars using the S2 data. The analysis procedure for S2 was more robust to interfering spectral lines and took advantage of the longer stationarity of the S2 data. Two hardware injections of hypothetical pulsars were injected in the LIGO interferometers during S2. The successful extraction of these signals from the LIGO S2 data significantly increased our confidence in the the overall data analysis pipeline. For four of the closest pulsars their equatorial ellipticities were constrained to less than = 10-5 with 95% confidence. These limits are beginning to reach interesting ellipticities which some exotic theories suggest could be supported in neutron stars. The third science run (S3) in which GEO 600 and LIGO participated took place from late October 2003 to early January 2004. Again, the improvement in sensitivity compared to the previous run (S2) was significant. Preliminary multi-detector results were determined for the same previous 28 pulsars using S3 data. The equatorial ellipticities for 11 of these pulsars are constrained to less = 10-5 with 95% confidence. With the S3 data, the upper limit on the gravitational wave emission from the Crab pulsar was only approximately a factor of four from the upper limits inferred from the spindown of the pulsar. When this barrier is overcome the prospects of detecting gravitational waves from the Crab pulsar will become more plausible. Future work based on these implementations will examine a larger set of missing known pulsars including binary systems. Studies in Markov Chain Monte Carlo techniques may also allow the expansion this method to a larger parameter space.

In a discipline commonly faulted for ad hoc assumptions and models with very little discriminating observational evidence, cosmologists are continually trying, and in many cases succeeding, to improve both the data and models. However, the desire to support currently favoured models often dominates research and may lead to a systematic bias being introduced in favour of a model before a strong body of supporting evidence has been accumulated. This is perhaps most evident in literature supporting the viability of Gamma Ray Bursts as cosmological distance indicators, where aside from subjective data-selection, the basic statistical methods are at best questionable and at worst incorrect. To this end, we construct a simple cosmology-independent illustration of the effect that the application of these methods has on parameter estimation and discuss the correct method to apply to current data. We also investigate the constraints potential future Gamma Ray Burst data may place on alternatives to the status quo Concordance Model in the shape of Conformal Gravity and Unified Dark Matter through a widely applicable and transferable Bayesian model comparison technique and the development of a representative mock data set. Finally, we investigate gravitational wave standard sirens as an alternative high-redshift distance indicator. We first illustrate their strong diagnostic potential through a Bayesian model comparison between the standard Unified Dark Matter model and a variant in which the dark component is redshift dependent. By drawing mock data from a known cosmological model, thus fixing the expected values of the model parameters, we find that while 182 Type 1a Supernovae are readily confused between constant and evolving models, just 2 standard sirens are able to successfully identify the correct model. Having established standard sirens as an effective tool in cosmological model comparison, we then address the potential confusion of models with dynamical dark energy and intrinsic curvature. We show that currently used distance indicators - Type 1a Supernovae, Baryon Acoustic Oscillations and the Cosmic Microwave Background Radiation - are not reliable enough to identify a small amount of intrinsic curvature, which partly justifies the common practice of assuming flat space in order to reduce the number of free parameters. However, we show that the addition of even a small number of standard sirens greatly reduces this problem. The addition of just two sirens offers a slight improvement, while adding ten sirens to the aforementioned list of indicators halves the range over which there is uncertainty between models.