The centrepiece of this thesis is a deep, new, high-resolution 1.4-GHz image covering the United Kingdom Infrared (IR) Telescope IR Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) legacy field. Deep pseudo-continuum observations were made using the Very Large Array, prior to its recent upgrade, in its A, B and DnC configurations. The resulting mosaic has a full-width-at-half-maximum synthesised beam width of ≈ 1.7 arcsec and a point-source sensitivity of ≈ 60μJy (6σ ) across the central 0.6 deg2, while conserving flux from sources of extended emission. The full image covers 1.3 deg2. I also present a catalogue containing over 1,000 radio emitters, having chosen the 6-σ threshold by maximising the number of radio sources with secure optical/near-IR counterparts. Most of the sources in the catalogue (≈ 90 per cent) lie in the sub-mJy flux density regime. Deep, complementary data covering a wide range of wavelengths was used to explore this faint radio population, whose nature remains controversial. It was found that 53 per cent of the sample comprise active galactic nuclei (AGN). AGN dominate at & 0.2mJy and remain a significant population down to 0.1mJy; at lower fluxes – the so-called μJy radio population – star-forming galaxies become dominant. The radio sample presented here was also matched to Hubble Space Telescope imaging of the UDS field (which is part of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey – CANDELS) to classify the faint radio population morphologically. These classifications were done using the Gini–M20 method. It was found that a low fraction of AGN and SFGs are undergoing interactions and mergers, 33 ± 9 and 13 ± 7 per cent, respectively. The merger fraction does not appear to have evolved significantly since z ∼ 3. This suggests that mergers have played a relatively minor role in the assembly of galaxies and super-massive black holes – certainly less significant than previously thought. Finally, I present a study of cosmic star-formation activity as a function of stellar mass and redshift, exploiting panchromatic stacking. Mid-IR–through–radio images, including new data from Herschel, are stacked at the positions of a K-selected (i.e. an approximately mass-selected) sample in the UDS field. Specific star-formation rates (SSFR, i.e. star-formation rate per stellar mass, or the rate at which a galaxy is converting its gas into stars) were derived from UDS radio luminosities measured here and stellar masses from the literature. The SSFR was found to be poorly correlated with stellar mass; it decreases with decreasing redshift; at a given mass, SSFR rises with redshift. These results indicate that at early epochs, galaxies were forming stars more efficiently and at a higher rate.

We present a novel new method for modelling magnetized molecular cloud cores using submillimetre linear polarization maps from thermal dust emission. Our PolCat modelling software builds a three-dimensional core model via the use of consecutive parametrized coordinate transformations, and produces simulated polarization maps to fit to observational datasets. We utilize the Ferret evolutionary optimizer to search the parameter space to simultaneously minimize chi-squared for the intensity and polarization position angle maps separately. We have applied PolCat to multiple test problems and several datasets from the SCUPOL Legacy Catalogue. We find that PolCat is able to distinguish between maps of twisted and non-twisted field geometries and identify twist symmetry. Preliminary fits to several datasets show that the best potential field geometries to our sample cores contain field twists. Further research using a larger number of maps is required to determine if twisted fields are commonplace in cores.

This study consists of a quantitative optical emission-line analysis of spectra from five blue compact galaxies (Zw 0855, Mrk 1267, II Zw 33, Tol 2 & Tol 3), as well as a qualitative analysis of spectra from two galactic H II regions (NGC 3603 & NGC 3576). It serves a two-fold purpose: first, to understand the CCD reduction, spectra extraction and different nebular analysis methods, together with their applications and limitations, preparatory to studies using the Southern African Large Telescope (SALT) and second, to extend current star formation related research to include extragalactic starburst galaxies. The observations were carried out using the 1.9m telescope (equipped with a grating spectroscope and CCD detector) of the South African Astronomical Observatory (SAAO), during the period 1 to 7 March 2005. The necessary CCD data reduction, spectra extraction, wavelength and flux calibration, Doppler shift as well as reddening correction procedures were performed before the emission lines were identified and measured. A full nebular analysis, including temperature, density, metallicity (oxygen abundance) and other chemical abundance determinations, was performed on the blue compact galaxies (BCGs). Two different nebular analysis packages viz. IRAF's nebular and SNAPwere used, with all the results well within the range of values expected for metal poor BCGs. Recommendations on the different methods and their applications are made. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2006.

Using data from the SCUBA Legacy Catalogue (850 µm) and Spitzer (3.6 - 70 µm), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. In particular, we focus on identifying which cores host young stars while others remain starless. Understanding the nature of star formation and the influence of local environment will give us insight into several key properties, such as the origin of stellar mass. Here, we present starless and protostellar core mass functions (CMFs) for the five clouds. We develop a new method to discriminate starless from protostellar cores, using Spitzer colours and positions. We found best-fit slopes to the high-mass end of −1.26±0.20, −1.22±0.06, −0.95±0.20, and −1.85±0.53 for Ophiuchus, Taurus, Perseus, and Orion, respectively. We were unable to fit a slope to our fifth cloud, Serpens. Broadly, these slopes are consistent with the −1.35 power-law seen in the Salpeter IMF, but suggest some differences. We examined a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and temperature. We also attempt to predict what future surveys with SCUBA-2 will detect in each of our clouds.

We investigate three separate topics associated with the formation and evolution of the stellar mass component in galaxy clusters. The work presented herein is based primarily on optical imaging and spectra taken with, respectively, the Canada-France-Hawaii Telescope and Gemini North/South. We confront the result from the optical data analysis with the results from the analysis of high-resolution X-ray data taken with the Chandra and XMM-Newton space observatories. Confirming earlier results, we find that 22% of brightest cluster galaxies (BCGs) show central inversions in their optical color profiles (blue-cores), indicative of recent star formation or AGN activity. Based on the extended sizes of the blue-core regions we favour recent star formation. Comparison with the host cluster central entropies (and other X-ray properties) demonstrates that the source of cold gas required to fuel the recent activity in BCG cores is direct condensation from the rapidly cooling intra-cluster medium. We measure the giant-to-dwarf ratio (GDR) of red sequence galaxies in a sample of 97 clusters to constrain its evolution over the redshift range 0.05 < z < 0.55. We find that the GDR is evolving and can be parameterized by GDR=(0.88 +/- 0.15)z+(0.44 +/- 0.03). We find that the intrinsic scatter in this relation is consistent with zero, after accounting for measurement error, Poisson noise and contributions from large-scale structure. After correcting for cluster mass effects we investigate the evolution of the individual dwarf and giant populations in order to probe the source of the observed GDR evolution. Beyond z=0.25 the GDR evolution is driven by an increase in the number of dwarfs (consistent with interpretations from the literature), however, below z=0.2 the GDR evolution is caused by a significant reduction in the number of giants. We interpret this a evidence for a significant number of major mergers in the giant population at late times. This is supported by the relatively short dynamical friction timescales for these galaxies. We use velocity-broadened stellar template models to fit the optical spectra of 19 BCGs in order to measure their the line-of-sight component of their central velocity dispersions (sigma). The sigma values are combined with previous measurements of effective radii re and effective surface brightness <I>e to investigate the properties of the BCG fundamental plane. We measure a BCG fundamental plane parameterized by log( re )= alpha log( sigma ) + beta log( <I>e ) + gamma, with best fit parameters alpha = 1.24 +/- 0.08, beta = -0.80 +/- 0.1 and gamma = (0.3 +/- 2.0)x10-4. We constrain the intrinsic scatter in this relation to be deltaint = 0.066 +/- 0.010 in re, consistent with previous measures of the scatter in the fundamental plane for regular cluster ellipticals. Comparing the slope parameters (alpha, beta) of the BCG FP to those from previous studies of the FP for regular cluster ellipticals, we find that there is no conclusive evidence for curvature in the unified FP. We use the sigma measurements to estimate the BCG dynamical masses Mdyn. Comparing these estimates with mass proxies for the clusters (Tx, ng) we find that BCG mass is independent of cluster mass with Mdyn = (2.9 +/- 1.8)x1012 solar masses. / Graduate / 0606 / 0605 / bildfell@uvic.ca

This dissertation presents new Herschel observations at 70 micron, 160 micron, 250 micron, 350 micron, and 500 micron of the Perseus molecular cloud from the Herschel Gould Belt Survey. The Perseus molecular cloud is a nearby star-forming region consisting of seven main star-forming clumps. The Herschel observations are used to characterize and contrast the properties of these clumps, and to study their embedded core populations. First, we probed the exceptionally young clump, B1-E. Using complementary molecular line data, we demonstrate that B1-E is likely fragmenting into a first generation of dense cores in relative isolation. Such a core formation region has never been observed before. Second, we use complementary long wavelength observations at 850 micron to study the dust properties in the larger, more active B1 clump. We find that Herschel data alone cannot constrain well the dust properties of cold dust emission and that long wavelength observations are needed. Additionally, we find evidence of dust grain growth towards the dense cores in B1, where the dust emissivity index, beta, varies from the often assumed value of beta = 2. In the absence of long wavelength observations, however, assuming beta = 2 is preferable over measuring beta with the Herschel-only bands. Finally, we use the source extraction code, getsources, to identify the core populations within each clump from the Herschel data. In addition, we use complementary archival infrared observations to study their populations of young stellar objects (YSOs). We find that the more massive clumps have an excess of older stage YSOs, suggesting that these regions contracted first. Starless cores are typically associated with peaks in the column density, where those found towards regions of higher column density also have higher average densities and colder temperatures. Starless cores associated with a strong, local interstellar radiation field, however, have higher temperatures. We find that the clumps with the most prominent high column density tails also had the highest fractions of early-stage YSOs. This relation suggests that the quantity of high column density material corresponds to recent star formation activity. / Graduate / 0606

Massive young star clusters and OB associations (M > 10 000 Msun) dominate the energetic feedback from stars into the interstellar medium. They contain the most massive and luminous stars in the Galaxy, which shape their environments through winds, ionizing flux, radiation pressure, and eventually supernovae, destroying their natal molecular clouds and inflating superbubbles. Few such clusters have been identified in our Galaxy. We systematically investigate the most luminous H II regions, which we identify using the WMAP foreground maps. We find that the 13 most luminous sources produce one-third of the Galaxy’s total ionizing luminosity, all with expected powering populations of M > 40 000 Msun. These populations are grouped in small numbers of clusters or associations for each WMAP source. The emission from these regions is dominated by the diffuse component at large radii (∼10-70 pc) indicating a high leaking fraction of ionizing photons. Using 8 μm maps from Spitzer GLIMPSE and published radio recombination line observations, we resolve the large (> 1◦) WMAP sources into 40 star forming complexes (SFCs) exhibiting shell morphology with evidence of expansion due to a central powering source. We develop a method, based on differential extinction of the galactic disk, to identify the SFC’s powering cluster candidates with 2MASS. We identify 22 cluster candidates within the 40 SFCs having extinctions consistent with their distances. With near-infrared spectroscopy from the New Technology Telescope, we have confirmed the existence of the most massive of these associations, the Dragonfish Association, with M = 100 000 Msun. Of the 50 sampled stars, we identify 2 Luminous Blue Variable candidates, a Wolf-Rayet, and 15 O-type stars, consistent with the yield expected from the candidate contamination rate, verifying the candidate cluster identification method. This investigation doubles the number of massive young star clusters and OB associations known and produces the most complete picture of the upper end of the Galaxy’s cluster mass function to date.

While the single core accretion model for low mass star formation is well developed, it cannot simply be extended into the high mass star formation regime where clustered star formation dominates. The study of intermediate-mass star formation should provide us with insights into how the process of star formation changes for high mass stars. In this thesis observations of H2O line emission from two intermediate-mass candidate Young Stellar Objects (YSOs) made using the HIFI instrument aboard the Herschel Space Observatory are presented. Modelling of molecular line emission using the radiative transfer code RATRAN is used to put constraints on kinematics and the abundance of water throughout the region by modelling the observed water lines after decomposing them into separate Gaussian components. The medium component of the 752 GHz line from Vela IRS 17 was modelled by using a turbulent velocity of 1.7 km s^-1 and an outer abundance of 6x10^-8. The narrow component of the 752 GHz line from Vela IRS 19 could be modelled using a turbulent velocity of 0.6 km s^-1 and an outer abundance of 6x 10^-8, while the medium component required an outer abundance of 4 x 10^-7 with a turbulent velocity of 2.5 km s^-1. The constraints on water abundance in these star-forming regions are to be used along with studies of water in low and high mass star-forming regions in the effort to improve our understanding of star formation across the entire stellar mass spectrum.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a 1.8 meter Cassegrain telescope that operates in three bands (250, 350, and 500 μm), each with 30% bandwidth. The detection system is comprised of 280 silicon-nitride micromesh bolometers distributed on three focal plane arrays with 30”, 42”, and 60” FWHM (full width at half max) beam sizes, respectively. BLAST's goal is to study the evolutionary history and processes associated with star formation. Earth's atmosphere is opaque to submillimeter radiation and astronomical observations in this wavelength are best conducted at high altitudes. BLAST is designed to be flown above 99.5% of the atmosphere on a stratospheric balloon. BLAST has made three scientific flights and this thesis covers the last two. The second flight was made in 2006 from McMurdo, Antarctica and studied the evolutionary history and processes associated with star formation. For the third flight, BLAST was reconfigured as a polarimeter (BLAST-Pol) and was also launched from McMurdo in December 2010. BLAST-Pol's objective is to determine what role, if any, magnetic fields play in star formation. This thesis will describe the BLAST-Pol instrument and provide a summery of key observations made by the 2006 flight.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23704号 / 理博第4794号 / 新制||理||1686(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 教授 長田 哲也, 准教授 細川 隆史 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM