No description available.

No description available.

In this thesis, we present a new photometric catalogue of the local Coma galaxy cluster in the Johnson U- and V- bands. We cover an area of 3360arcmin(^2) of sky, to a depth of V = 20mag in a 13 arcsec diameter aperture, and produce magnitudes for ~ 1400 extended objects in metric apertures from 8.8 to 26arcsec diameters. The mean internal RMS scatter in the photometry is 0.014mag in V, and 0.026mag in U, for Via(_13) < 17mag. We use this photometric catalogue to place limits on the levels of scatter in the colour- magnitude relation (CMR) in the Coma cluster. We subdivide the galaxy population by morphology, luminosity and position on the sky, and analyse the CMR in each of them. The lowest levels of scatter are found in the elliptical galaxies, and the late type galaxies have the highest numbers of galaxies blue-wards of the CMR. We finds signs of decreased scatter and systematically bluer galaxy colours with increasing projected radius from the center of the cluster, and attribute it to a mean galactic age gradient. We find that the typical mass of galaxies within clusters can increase by a factor of two through dissipationless merging without destroying the CMR. We compare the spectral line indices of galaxies in the Coma cluster with their deviation from the mean colour-magnitude relation (CMR). We find that the CMR in Coma is driven primarily by a luminosity-metallicity correlation, however we cannot rule out a contribution from age effects. Colour deviations blue-ward of the mean relation are strongly correlated with the Hydrogen Baimer line series absorption, indicating the presence of a young stellar population in these blue galaxies. We use a wavelet code to suggest an association between X-ray cluster substructure and 'E+A' galaxy activity in high redshift clusters.

We have acquired near-IR H and optical $g$,$r$,$i$,$z$ imaging for a sample of 299 Virgo cluster galaxies down to a limiting magnitude of B$_T$=16.0 mag. The low sensitivity of near-IR wavelengths to dust extinction is crucial for an unbiased geometric deprojection of fundamental galaxy parameters. We find, in agreement with Tully and Verheijen (1997), a clear dichotomy between high and low surface brightness galaxy disks. The difference between the low and high brightness peaks of Virgo galaxies is $\sim$2 H-mag arcsec$^{-2}$, significantly larger than any systematic errors. The high surface brightness galaxies have two distinct classes of bulge with high and low concentration, while low surface brightness galaxies have only low concentration bulges. The distribution of the effective surface brightnesses of our entire sample shows that early-type galaxies exhibit a similar structural bimodality though offset from that of spiral galaxies towards higher surface brightnesses. We find that the structural bimodality is uncorrelated with colour or any other structural parameter except, perhaps, the circular velocity. Simulations of realistic surface brightness profiles show that a bimodality in effective surface brightness is unexpected based on normal distributions of fundamental bulge and disk parameters. Rather, the structural bimodality is likely linked to the galaxy dynamics, namely the specific angular momentum of the galaxy; high surface brightness galaxies have low angular momentum and can collapse to form dynamically important disks, while low surface brightness galaxies are dominated by the dark halo everywhere. Finally, our bulge-disk decompositions of all the sample galaxy images using various fitting functions have revealed that galaxies of all morphologies, including flattened and spheroidal systems, exhibit a ``disk'' component which is best described by a generalized ``Sersic'' function. We also find that the majority of galaxy disks show significant deviations from a pure exponential. Further dynamical studies of both cluster and field galaxies are needed to properly explain the observed structural bimodality in both early- and late-type galaxies. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2007-08-10 10:04:56.651

No description available.

This thesis is concerned with the physics of extragalactic radio - sources. Radio observations of a given source provide a powerful method with which to make direct measurements of the physical processes occuring within the la~ge-scale radio lobes and hotspots . Multi-frequency observations with up to five frequencies have been made for a number of ~ources using the Cambridge 5-km telescope and the Very Large Array. These data have been used to determine the change in radio spectra across the source . to obtain information about the way in which the electron population has evolved. Combining this with inferred magnetic field directions, the dynamics of seven sources have been examined. Additionally the hotspot advance speeds for a statistically representative sample of sources have -been derived. For 3C234 it was possible to test the assumptions used throughout the analysis. They were found to h6ld good to within the limits of error. The results are best interpreted within the framework of a fluid-dynamical model lobes as have recently been examined in numerical experiments. The general distibution of radiating plasma can be understood in terms of the flow of material out of the main accelerating regions (the hotspots - a basic beam model � is assumed thr6ughout) and its subsequent interaction with the surrounding medium, coupled with some precession of the radio jet. As well as looking at source dynamics , the detailed spectra have been used to search for areas of particle acceleration not associated with hotspots. Three sources have been found to have such regions, but large scale acceleration within the radio-lobes is not required . The derivation of ho tspot advance speed for a statistically representative sample has enabled statistical correlations to be investigated . Advance speed is found to be strongly correlated with power and this is discussed in the wider context of overall source models.

A significant fraction of the star formation density between z = 1–3 has been traced to luminous and ultra-luminous infrared galaxies. Among the most extreme objects seen are those identified via surveys at submillimetre wavelengths; the high infrared luminosities (LIR = 10¹¹−¹³ L⊙) of these “submillimetre galaxies” (SMGs) arise due to the reprocessing of UV and optical light from massive, young stars by interstellar dust, and imply star formation rates SFR= 50–2000M⊙ yr−¹. Such SFRs, combined with the observed increase in number density of SMGs by a factor ∼ 20× out to z = 2 make them candidates to be the progenitors of the most massive “red and dead” elliptical galaxies which dominate the cores of clusters in the present day, yet limitations in the technical capabilities of radio and infrared telescopes have long hindered a detailed understanding of these galaxies, and in particular, the physics of the interstellar medium (ISM). Hence the following key questions remain unanswered: (i) how much molecular gas (H2) do SMGs contain, and what are the likely upper-limits on how long they can sustain their present level of activity?; (ii) do the prodigious luminosities of SMGs stem from a common origin, or does the selection criterion return a “mixed bag” of galaxies?; (iii) what are internal kinematics of SMGs, and to what extent do these influence the global and local star-formation (Schmidt-Kennicutt) law?; (iv) is star-formation in distant SMGs distributed across the entire galaxy, or does it occur in isolated clumps?; (v) what are the typical densities and temperatures of star-forming regions in SMGs, and do they adhere to the observed correlation between far-infrared and radio emission in star-forming galaxies? Recent upgrades to the Karl G. Jansky Very Large Array (VLA), the inauguration of the Atacama Large Millimeter Array (ALMA), and the superlative legacy of the Herschel Space Observatory have jointly provided the toolkit to study the gas and dust emission in distant galaxies in unprecedented detail, and thus to begin to address these fundamental questions. In this thesis, I present ∼120 hours of new VLA observations of ¹²CO J =1−0 emission – the best tracer of molecular gas – in a sample of four lensed SMGs. The combination of high angular resolution with the VLA and the magnifying effects of gravitational lensing allow the ISM properties of these z ∼ 2.5 star-forming galaxies to be seen for the first time on sub-galactic scales, implying gas masses of 10⁹−¹ºM⊙ (subject to the 12CO-luminosity-to-H2-mass conversion factor, αCO), and demonstrating the presence of an extended, low-excitation gas reservoir. In conjunction with observations of the excited gas phase from the Plateau de Bure Interferometer (PdBI), these new data point to variations in the densities and temperatures of H2 throughout each galaxy. The wide bandwidth and phenomenal sensitivity of the VLA yields the first detections of 115-GHz continuum emission at high redshift, which I use in conjunction with well-sampled dust spectra from Herschel and data at longer wavelengths from the VLA to decompose the radio spectra of two galaxies into contributions arising from thermal dust emission, optically-thin free-free emission from Hii regions, and non-thermal synchrotron emission. From these measurements, estimates of SFRradio are made, providing an independent check on SFRIR, and enabling the degeneracy between the heating of dust due to star formation and that due to hidden AGN activity to be broken. Via this spectral index de-convolution, I find L[AGN]/LIR fractions of 35% and 55% for the two SMGs, in broad agreement with previously published estimates for these sources based on their mid-IR spectral properties. In the exceptional case of SMMJ23152–0102, magnification by the foreground cluster is so extreme (∼ 32.5×) that the VLA synthesised beam traces regions of order ∼ 130 pc in the source plane, and identifies a series of cool, dense clumps (Tk = 30–70 k; log[n(H2)/cm−3]= 3.6–3.9) within the gas reservoir, which contain between them 10–60% of the total molecular gas of the system. These clumps are offset from the far-infrared/radio correlation, which I argue has implications for their ages.

This thesis investigates the morphology of early-type galaxies in two rich clusters using 2D surface photometry. In particular, the amount of light in the 'disk' component is focussed upon, as the presence of a disk is the main morphological criterion in distinguishing between the traditional 'elliptical' and 'S0' classes. Extensive and photometric E-band CCD observations of continuous areas of the Coma and Abell 1367 clusters were obtained at the 2.5 m Isaac Newton telescope, La Palma during March 1994. A subset of this large data-set has been used in this study, comprising a magnitude-limited (to R = 15.6) sample of 153 galaxies in the two clusters. Surface photometry measurements, including surface brightness profiles and isophotal shapes, have been made for the sample. Atmospheric seeing is a major problem when measuring light profiles at the distance of Coma from ground-based telescopes. Typical seeing at La Palma (FWHM~1.2") is a significant fraction of the effective radius of many Coma/Abell 1367 galaxies (r(_e)~3" for small ellipticals). An iterative algorithm was developed to deconvolve the effects of seeing from surface brightness profiles. The result of the algorithm is to extend the range of useful surface photometry inwards to within 2 times the FWHM. In order to parametrise the surface brightness profiles and discriminate between different profile-types, further software was developed to fit one- and two-component model profiles to the seeing-corrected data. The following parameters were measured and tabulated for each of the 153 galaxies: total magnitude M(_t); half-light parameters r (_1/2) and (μ)(_1/2); SB at half-light radius μ(r(_1/2)); photometric diameter D(_19.23) (equivalent to D(_n)); ellipticity at R = 21.5 isophote ϵ(_21.5); averaged isophote high-order terms (C(_3)), (S(_3)), (C(_4)) and (S(_4)); effective radii and surface brightnesses of 5 single power-law r(^1)(_n) models, r"e and (^)"^ (n = 1,2,3,4,5); best-fitting power-law index n; bulge effective radii and surface brightnesses from the two-component fit and (/^)\; disk effective parameters r'^e and {nY^] and disk-to-bulge luminosity ratio DjB. The measured parameters have been used to investigate various aspects of early-type galaxy morphology. The conclusions are outlined below. Firstly, a two-component r? plus exponential model is a better fit to most galaxies than a single component law fit. Secondly, the traditional division of early-type galaxies into 'elliptical' and 'SO' classes is severely biased by the viewing angle. In fact, it appears that early-type galaxies comprise a population of objects with smoothly varying bulge-to-disk ratio - although a few ellipticals (less than 13%) do not appear to have a exponential component. Finally, there is a general correlation (with much scatter) between the size and the profile shapes of early-type galaxies. The interpretation is that smaller galaxies are more disk-dominated than larger galaxies, which can be linked to the merging process in rich clusters.

Dwarf galaxies are powerful tools in the study of galactic evolution. As the most numerous galaxies in the universe, they probe a diverse range of environments: some exist in near-isolation, allowing us to study how a galaxy’s evolution depends on its intrinsic properties. Others have been accreted by larger galaxies and show the impact of environmental processes such as tidal stripping. Because dwarf galaxies have shallow potential wells, these processes leave strong signatures in their star formation histories (SFHs). We use state-of-the-art cosmological hydrodynamical simulations to study the evolution of dwarf galaxies in Local Group analogues. Their SFHs are remarkably diverse, but also show robust average trends with stellar mass and environment. Low- mass isolated dwarfs (10^5 < M∗/M⊙ < 10^6) form all of their stars in the first few Gyr, whereas their more massive counterparts have extended star formation histories, with many of the most massive dwarfs (10^7 < M∗/M⊙ < 10^9) continuing star formation until the present day. Satellite dwarfs exhibit similar trends at early and intermediate times, but with substantially suppressed star formation in the last ∼ 5 Gyr, likely as a result of gas loss due to tidal and ram-pressure stripping after entering the haloes of their primaries. These simple mass and environmental trends are in good agreement with the derived SFHs of Local Group dwarfs whose photometry reaches the oldest main sequence turnoff. SFHs of galaxies with less deep data show deviations from these trends, but this may be explained, at least in part, by the large galaxy-to-galaxy scatter, the limited sample size, and the large uncertainties of the inferred SFHs. / Graduate

The Andromeda Galaxy (M31) is an ideal target for detailed studies of galaxy structure and tests of stellar population models. This thesis presents deep Canada-France-Hawaii Telescope WIRCam near-infrared J- and Ks-band photometric maps of M31. These near-infrared data alleviate the age-metallicity-dust degeneracy that plagues stellar population analysis of optical-only maps. For the sake of calibrating stellar population models, a detailed reconstruction of the M31 near-infrared surface brightness and a study of sky subtraction uncertainties is needed. The analysis of our 2007 and 2009 WIRCam data has revealed unexpected spatial variations in the sky background shapes over the width of the WIRCam fields. In order to solve for the offset caused by such fluctuations, we have used couplings between images. Scalar sky offsets are optimized to produce a mosaic that is seamless within 0.02% of the sky background. These offsets are solved hierarchically, to reduce the dimensionality of optimizations, and an adaptation of the Nelder Mead downhill simplex ensures a globally optimal solution. Variations in sky shape are well-characterised in median sky images built by nodding to a random ring of sky fields every 1.2 minutes. Sky shape appears consistent across the 3˚ ring of sky fields, while levels do change by ~2%, suggesting that the dominant sky structures extend beyond the M31 survey region. Planar sky offset optimization was tested and promises to significantly improve continuity across the outer disk of M31. Our near-infrared data are part of an effort to assemble a multi-wavelength data set for M31 to study a broad suite of topics in stellar and galaxy evolution. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-12-07 15:34:00.279