The study of low mass star formation in our local Galaxy is particularly suited to HERSCHEL. The SPIRE spectrometer and photometer aboard the spacecraft operate in the ~ 200 - 600�m range and are well suited to probe the cold, dusty environments in molecular clouds where prestellar cores reside. The SPIRE FTS spectrometer is an interferometer, and this instrument design has strengths and weaknesses which are im- portant to understand when using data from the instrument. Herschel is set to continue groundbreaking work in the infrared, building upon earlier work from ISO, IRAS, and SPITZER, probing deep into star forming regions and improving our knowledge of the processes within. In this PhD thesis, we outline the current body of knowledge in low mass star formation. We examine the properties of the SPIRE FTS as a spectrometerusing a small, laboratory designed desktop FTS. We study the intrinsic properties of the instrument, as a way of understanding issues we are likely to see when using the SPIRE FTS in ight. With these issues firmly in mind, we examine the creation and use of SLIDE - an interactive IDL-based tool for processing SPIRE FTS data. SLIDE can extract line and continuum information from SPIRE FTS SEDs. We outline the creation, testing and use of SLIDE and provide examples of the use of SLIDE in astronomy with some examples from the literature. We then use the line information we extract from a variety of sources with the spectrometer, to examine how SED fitting from photometer data could be affected by line contamination. We simulate a wide range of greybodies with noise and line con- tamination and examine how SED fitting is affected. Our simulations conclude that line contamination is not enough to affect the recovery of temperature and spectral index B significantly. Finally we use the information we have deduced to examine SPIRE FTS SEDs of L1689B - a prestellar core located in Ophiuchus. Our SED fitting of the core confirms that this core is starless with no internal heating source, and the spectral index profile over the core morphology is consistent with an increasing density of fractal aggregrate grains towards the centre. The increase in grain density and spectral index profile is also in agreement with previous CO depletion data. Fractal grain growth of this nature is consistent with dust grain models.

Understanding the history of the formation of stars and evolution of galaxies is one of the foremost goals of astrophysics. While stars emit most of their energy at visible and ultraviolet wavelengths, during the early stages of star formation these photons are absorbed by the dusty molecular clouds that host and fuel the emerging stars, and re-emitted as thermal radiation at infrared and submillimeter wavelengths. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) was designed to study the history of obscured star forma- tion in galaxies at cosmological distances and witness the details of the star-formation processes in our own Galaxy, by conducting large- area surveys of the sky at 250, 350, and 500 �m from a long-duration stratospheric balloon platform. Its polarimetric adaptation, BLAST- Pol, will allow us to further probe the strength and morphology of magnetic fields in dust-enshrouded star-forming molecular clouds in our Galaxy. The study of these two diverse, yet highly complemen- tary, topics is the primary scientific motivation for this thesis, which is in two parts. Part One is concerned with the analysis of a combination of the extragalactic dataset collected by BLAST in the 2006 Antarctic cam- paign, which comprises maps containing hundreds of distant, highly dust-obscured, and actively star-forming galaxies, with a wealth of ancillary multi-wavelength data spanning the radio to the ultravio- let. The star-formation rates we observe in massive galaxies at high redshift support downsizing and size evolution. Part Two describes the BLAST-Pol instrument. In particular, we focus on the gondola's primary pointing sensors, the star cameras, and on the design, manufacture and characterization of a polarization IX modulation scheme, comprising a cryogenic achromatic half-wave plate and photolithographed polarizing grids, which has been effectively retrofitted on BLAST-Pol. We report on the construction and deployment of BLAST-Pol, which completed its first successful 9.5-day ight over Antarctica in January 2011 and mapped ten science targets with unprecedented combined mapping speed, sensitivity, and resolution.

ABSTRACT High mass stars affect their environments on a large scale. However, the processes behind the formation of high mass stars are still relatively poorly understood compared to their low mass counterparts. Infrared dark clouds (IRDCs) and their cold cores (gravitationally bound cores embedded within the IRDCs) are thought to be the earliest observable stage of high mass star formation. By observing these very young regions we gain insight into the formation of high mass stars. IRDCs were initially found as regions of extended absorption in the midinfrared (MIR). However, identifying IRDCs in the MIR alone can create problems because there is no way to distinguish between IRDCs and minima in the MIR background. In this thesis we use data taken by the Herschel Infrared Galactic Plane Survey to observe IRDCs and their cold cores at wavelengths where they are expected to be seen in emission, i.e. in the far-infrared (FIR).

Multiple observations of distant type Ia supernovae show the deceleration parameter of the universe is negative. The standard cosmological model states expansion should be slowing down. A new theory is presented which explains cosmic acceleration only through the action of well-supported phenomena in the context of Einstein's general theory of relativity through the use of the Bianchi type IX homogeneous,closed cosmology. The evidence for acceleration is assessed and previously-unreported biases and insuffiencies in the evidence are revealed and discussed. The Einstein equations for the Bianchi type IX cosmology are solved to quadratic order in a matter-dominated universe. The first terms of a power-series solution are given for arbitrarily strong growing mode of gravitational waves in a matter-dominated Bianchi IX universe. The effect of these waves on the energy density of the universe is shown to becompatible with available data. The equations for redshift anisotropy in the Bianchi IX universe are solved to quadratic order. Reported anomalous structure in the cosmic microwave back-ground is considered in the light of these solutions. The Bianchi IX universe is shown to provide an explanation for these anomalies compatible with the CMB. In order to help typify a new class of standard sour es for determining cosmological parameters, a formula relating the time-dependent detection of light by a massive, compact binary such as a super-massive black hole binary is derived. This formula is applied to the system 3C66B and finds that in ideal circumstances, the best available observational techniques would detect a time-dependent omponent to the bending of light by the core of 3C66B. A solution for the Einstein equations in the Bianchi IX universe is found which explains cosmic acceleration while remaining compatible with the CMB and other cosmological parameters as reported by WMAP.

In this thesis, I present BLAST observations of the Carina Nebula and Herschel observations of NGC7538. I use the source extracting routine CSAR to identify 172 source in Carina and 94 sources in NGC7538. I fit SEDs to all the sources and calculate their mass, luminosity, temperature and radius. For the Carina Nebula I find a mass range of 20 – 10 4M¯, a luminosity range of 10 2 – 10 5 L¯, a temperature range of 16 – 28 K, and source radii range of 0.3 – 3.2 pc. For NGC7538 I find a mass range of 5 – 10 3M¯, a luminosity range of 5 – 10 3 L¯, a temperature range of 10 – 40K and a source radii range of 0.1 – 2 pc. I cross - check the source extraction method using the routine, GETSOURCES. This algorithm found a total of 621 sources in NGC7538. The GETSOURCES catalogue is filtered to removed sources which are present in two or less wavelengths. This filtered catalogue then has a good correlation with the CSAR catalogue. Using both catalogues a robust source list of 75 sources is created from sources found by both routines. I plot the mass against radius for both the Carin Nebula and NGC7538. For Carina the data are best fitted by M / R1.8 which is comparable to the Larson relation of M / R2. In NGC7538 I find no relation. I find no temperature dependence in the Carina Nebula with any other source property but find a weak relation between temperature and luminosity in NGC7538. Both regions show a relation of L / M. I find a relation between radius and Luminosity per unit volume where smaller sources have a higher luminosity per unit volume and the larger sources have a lower value. I find sources with a luminosity per unit volume less then 1L¯pc−3 tend to lie in the less dense regions of the nebulae and sources with a luminosity per unit volume greater then 3.5L¯pc−3 lie in the denser regions where the more evolved sources tend to be. This could show that the luminosity per unit volume can trace the evolutionary status of sources in a region.

Accurate stellar parameters are important not just to understand the stars themselves, but also for understanding the planets that orbit them. Despite the availability of high quality spectra, there are still many uncertainties in stellar spectroscopy. In this thesis, the finer details of spectroscopic analyses are discussed and critically evaluated, with a focus on improving the stellar parameters. Using high resolution, high signal-to-noise HARPS spectra, accurate parameters were determined for 22 WASP stars. It is shown that there is a limit to the accuracy of stellar parameters that can be achieved, despite using high S/N spectra. It is also found that the selection of spectral lines used and the accuracy of atomic data is crucial, and different line lists can result in different values of parameters. Different spectral analysis methods often give vastly different results even for the same spectrum of the same star. Here it is shown that many of these discrepancies can be explained by the choice of lines used and by the various assumptions made. This will enable a more reliable homogeneous study of solar-like stars in the future. The Rossiter-McLaughlin effect observed for transiting exoplanets often requires prior knowledge of the projected rotational velocity (v sin i). This is usually provided via spectroscopy, however this method has uncertainties as spectral lines are also broadened by photospheric velocity fields known as “macroturbulence” (vmac). Using rotational splitting frequencies for 28 Kepler stars that were provided via asteroseismology, accurate v sin i values have been determined. By inferring the vmac for 28 Kepler stars, it was possible to obtain a new calibration between vmac, effective temperature and surface gravity. Therefore macroturbulence, and thus v sin i, can now be determined with confidence for stars that do not have asteroseismic data available. New spectroscopic vsini values were then determined for the WASP planet host stars.

Lenticular (S0) galaxies have long been thought of as evolved spirals, in which the star formation has been suppressed, the spiral arms have faded, and the luminosity of the bulge has been built up relative to the disc. However, the sequence of events that explains these three observations and leads to the formation of the final S0 galaxy is still uncertain. The progenitor spirals generally consist of bulges with old stellar populations surrounded by young, bright discs. Therefore, in order to explain the `quenching' of star formation in the disc and related increase in the bulge luminosity, an understanding of the individual star-formation histories of these two components is vital. In this thesis, we present a new technique to spectroscopically decompose the light from a galaxy into its bulge and disc components, from which the stellar populations and chemical compositions of the individual components can be extracted in order to determine the sequence of events leading to the transformation. Using spectroscopic bulge-disc decomposition, the spatial light profile in a two-dimensional galaxy spectrum can be separated wavelength-by-wavelength into bulge and disc components. This decomposition allows the construction of separate one-dimensional spectra representing purely the light from the bulge and disc, enabling studies of their individual star-formation histories with minimal contamination. This technique was applied to a sample of 30 S0s in the Virgo and Fornax Clusters, and analysis of the absorption line strengths within these spectra reveals that the bulges contain consistently younger and more metal-rich stellar populations than their surrounding discs. This result implies that the final episode of star formation before the progenitor spirals were fully quenched occurred in their central regions. Furthermore, the similarity in the alpha-element abundances of the bulges and discs indicates that the final episode of star formation in the bulge was fuelled using gas that has previously been chemically enriched in the disc. Together, these results present a picture in which the galaxy starts out as a typical spiral, with an old bulge surrounded by a young, star-forming disc. At some point in its life, gas is stripped from the galaxy, suppressing the star formation in the disc and causing the spiral arms to fade without inducing significant amounts of new star formation or disrupting the overall morphology of the galaxy. As the gas is removed, a fraction is also driven into the centre of the galaxy, where it fuels a final star-formation event in the bulge. This final episode of star formation consequently increases the luminosity of the bulge as the disc is already fading, and produces a central young, metal-rich stellar population. We have also shown that it is possible to spectroscopically decompose a galaxy using the different line-of-sight velocity distributions of kinematically distinct components. This technique was applied to NGC~4550, an unusual S0 galaxy in the Virgo Cluster with two counter-rotating stellar discs and a gaseous disc, to separate their individual stellar populations. Analysis of these stellar populations shows that the disc that co-rotates with the ionized gas is brighter and has a significantly younger mean age than the other disc, which are consistent with more recent star formation fuelled by the associated gaseous material. Therefore, the most likely formation mechanism for this galaxy is via an unusual gas accretion or merger scenario that built up a secondary stellar disc in a pre-existing S0 galaxy. The results presented in this thesis shed new light on the sequence of events that leads to the formation of S0 galaxies in cluster environments, and clearly demonstrates the importance of understanding the star-formation histories of the individual components within these galaxies in order to reconstruct the range of mechanisms by which they formed.

USING multiwavelength observations, centred around the unique far-infrared and submillimetre window provided by the Herschel Space Observatory, this thesis investigates the origins and evolution of cosmic dust in the local Universe – by examining individual sources of dust in our own galaxy, and by studying dust in nearby galaxies. Herschel observations of the remnants of Kepler’s (SN1604) and Tycho’s (SN1572) supernovae, both Type-Ia explosions, are searched for evidence of dust creation by these events. Being the only Type-Ia supernovae known to have occurred in our Galaxy within the past 1,000 years, these remnants are the only ones both close enough to resolve, and young enough that they are dominated by their ejecta dynamics. There is no indication of any recently manufactured dust associated with either supernova remnant. It therefore appears that Type-Ia supernovae do not contribute significantly to the dust budgets of galaxies. The Crab Nebula, the result of a Type-II supernova (SN1054), is also investigated using Herschel and multiwavelength data. After accounting for other sources of emission, a temperature of Td = 63.1K and mass of Md = 0.21M⊙ is derived for the Crab Nebula’s dust component. A map of the distribution of dust in the Crab Nebula, the first of its kind, is created by means of a resolved component separation, revealing that the dust is located in the dense filamentary ejecta. We can be confident that this dust will survive in the long term, and be injected into the galactic dust budget. This is the first detection of manufactured supernova dust for which this can be said. I next use the Herschel-ATLAS to assemble HAPLESS: the Herschel-ATLAS Phase-1 Limited Extent Spatial Sample – a blind, volume-limited, dust-selected sample of nearby galaxies. The majority of this sample is made up of curious very blue UV-NIR colours, these galaxies appear to be prominent in the local dusty universe. In the absence of reliable photometry for the HAPLESS galaxies, I describe the function and testing of a purpose-built photometric pipeline – CAAPR: Chris’ Adequate Aperture Photometry Routine. The photometry conducted with CAAPR exhibits flux greater by factors of, on average, 1.6 in the FUV and 1.4 in r-band, relative to the previously-available photometry.

The main goal of this thesis is to test the viability of some modified theories of gravity suitable to describe gravitational phenomena at cosmological and astronomical scales. In the first part of the Thesis we study the viability of the Brans-Dicke theory (BDT) and the effective scalar-tensor theory according (gBDT) to cosmological observations. We assume that either BDT as gBDT are limiting cases on very large scales of more general scalar-tensor theories involving derivative self-interactions which have running Newton’s constant. In order to implement this assumption in a simple way we consider two types of models. The restricted models that correspond to the standard BDT with Newton constant today equal to measured Newton constant in solar-system experiments. The unrestricted models, correspond to the case where the Newton’s constant today is a free parameter, and the cosmological GN is allowed to be different than in the solar system as in more general theories. We first explore the relevant theoretical aspects of these models. Afterwards, by using different analysis techniques we fitted cosmological observations. Finally we forecast limits of BDT by considering estimated covariance matrices for measurements of the matter power spectrum in redshift space from Euclid. The effective scalar-tensor theory gBDT arises from a phenomenological setup of parametrization of the LSS growth equations, we found estimates of modifications of the growth by using the correspondance between the estimates for the gBDT parameters. In the second part of the Thesis we present an extension of the Parameterized Post-Newtonian (PPN) formalism that is able to handle Vainsteinian corrections. We argue that theories with a Vainshtein mechanism must be expanded using two small parameters. In this Parameterized Post-Newtonian-Vainshteinian (PPNV) expansion, the primary expansion parameter which controls the PPN order is as usual the velocity v. The secondary expansion parameter, α, controls the strength of the Vainshteinian correction and is a theory-specific combination of the Schwarzschild radius and the Vainshtein radius of the source that is independent of its mass. We present the general framework and apply it to the Cubic galileon theory both inside and outside the Vainshtein radius. The PPNV framework can be used to determine the compatibility of such theories with solar system and other strong-field data.

This thesis describes the development and testing of two cold-electron bolometers using highly-doped silicon as the absorber. These detectors exhibit both high sensitivity and low time constants. High sensitivity is achieved due to the weak thermal-link between the electrons and the phonons in the silicon absorber at low temperature (< 1 K). Schottky barriers form naturally between the highly-doped silicon absorber and the superconducting contacts. Selective tunnelling of electrons across these Schottky barriers allows the electron temperature in the silicon absorber to be cooled to below the thermal bath temperature. This direct electron-cooling acts as thermoelectric feedback, reducing the time constant of a cold-electron bolometer to below 1 µs. In this work, the underlying physics of these devices is discussed and two devices are presented: one with a highly-doped silicon absorber and the other with strained highly-doped silicon used as the absorber. The design of these detectors is discussed and results are found from numerous characterisation experiments, including optical measurements. These measurements show that a prototype device, using a strained and highly-doped silicon absorber, has a noise-equivalent power of 6.6 × 10^-17 W/rtHz. When photon noise (which dominated this measurement) and noise from the amplifier are disregarded, the underlying device-limited noise-equivalent power is 2.0 × 10^-17 W/rtHz. By measuring the photon noise, the time constant of this detector has been determined to be less than 1.5 µs. When compared to the device using unstrained silicon, it is clear that the straining of the silicon absorber, which reduces the electron-phonon coupling, produces a notable improvement in detector performance. Furthermore, a novel amplifier-readout technique, whereby the outputs of two matched amplifiers are cross correlated is introduced; this technique reduces the input-referred amplifier noise from 1 nV/rtHz to 300 pV/rtHz.