Chemical elements synthesized in stars are released into the interstellar medium (ISM) from discrete and localized events such as supernova (SN) explosions and stellar winds. The efficiency of transport and mixing of the new nucleosynthesis products in the ISM determines the degree of chemical inhomogeneity in the galaxy, which is observable in objects of the same age, such as coeval stars and the ISM today. It also has implications for the transition from metal-poor to normal star formation in high-redshift galaxies. We develop a physical mixing model for chemical homogenization in the turbulent ISM of galaxies using modern theories and methods for passive scalar turbulence. A turbulent velocity field stretches, compresses and folds tracers into structures of smaller and smaller scales that can be homogenized faster by micro-scopic diffusivity, the only physical process that truly mixes. From a model that incorporates this physical process, an evolution equation for the probability distribution of the tracer concentration is derived. Including the processes of new metal release, infall of low metallicity gas and incorporation of metals into new stars in the equation, we establish a new approach to investigate chemical inhomogeneity in galaxies: a kinetic equation for the metallicity probability distribution function, containing all the 1-point statistical information of the metallicity fluctuations. Motivated by a recent interpretation of ultraviolet properties of high-redshift Lyman Break Galaxies, we apply this approach to study mixing of primordial gas in these galaxies and find that primordial gas can survive for ~ 100 Myr in the presence of continuous metal sources and turbulent mixing if the unlikely efficient mixing in SN shells is excluded. Recent observations show that the Galaxy has been extremely homogeneous during most of its history. In an attempt to understand the homogeneity using our approach, we find that standard chemical evolution models without infall give metallicity scatters consistent with observations while all the infall models produce scatters at least 5 times larger than observed. To avoid this discrepancy and to remain a valid solution to the G-dwarf problem, the main motivation for infall models, the infall gas is required to primarily consist of small clouds of size less than ~ 5 pc. Fluctuations in the carbon to oxygen abundance ratio are of astrobiological interest: regions with C>O are likely to be devoid of water, which is thought to be essential for life. A small degree of inhomogeneity in the ratio gives a finite probability for the existence of regions with C>O even when the average ratio is smaller than unity. As the mean C/O ratio increases, as supported by observations and theoretical models, the Galaxy will eventually make a transition from mostly oxygen-rich to mostly carbon-rich. To the extent that life requires liquid water, the formation of habitable planets would no longer be possible. Adopting a negative Galactic C/O radial gradient, the transition appears as an outward-moving dehydration wave from the inner regions of the Galaxy. Finally we examine the effect of turbulent stretching on nuclear flames in Type Ia Supernova (SN Ia) progenitors. Turbulent stretching exhibits strong intermittency at small scales where its probability distribution shows a broad tail, corresponding to intense but rare stretching events. These events have important implications for the flame burning state and thus for the deflagration to detonation transition (DDT) in SN Ia explosions. Current DDT models require a critical turbulent intensity or stretching over a flame region that is sufficiently large. We find that including local intermittent stretching in these models results in a shift toward larger transition densities at which the DDT occurs. / text

No description available.

Stellar bars are the most important internal drivers of the evolution of disk galaxies because they efficiently redistribute mass and angular momentum in the baryonic and dark matter components of galaxies. Mounting evidence suggests that mechanisms other than major mergers of galaxies, such as minor mergers, gas accretion, and bar-driven secular processes, play an important role in galaxy evolution since a redshift z~2. In order to characterize the evolution of barred disks, this thesis presents one of the most comprehensive studies of barred galaxies in the field at low redshifts, and also as a function of environment across galaxy clusters of different densities. This work improves significantly on earlier studies by using quantitative methods to characterize bars, analyzing high-quality data from some of the largest disk galaxy samples to date, and using results across a range of Hubble types and environments to test different theoretical models for the evolution of disk galaxies. Our main results are summarized below: (1) Studies done as a part of this thesis have quantitatively shown for the first time that the optical bar fraction in z~ 0 field galaxies is a sensitive and non-monotonic function of host galaxy properties, such as the luminosity, stellar mass, and bulge-to-disk ratio. We find that at z~0, the bar fraction increases significantly from galaxies of intermediate mass and Hubble types (Sb) toward those of lower mass and late Hubble types (Sd-Sm). The behavior from intermediate to early Hubble types is more uncertain. These results, which have been subsequently confirmed by independent studies, set constraints for theoretical models and in particular underline the importance for bar growth of angular momentum exchange between the bar, disk, bulge, and dark matter halo, as well as the possible triggering of bars by external satellites and interactions with the dark matter. Furthermore, our results at optical and near-infrared wavelengths on the fraction and sizes of bars at z~0 provide the zero-redshift anchor point for studies of bars at higher redshifts with current and future space missions (e.g., ACS, WFC3, JWST), and allow us to assess the systematic effects in such studies. (2) Although cluster environments are unique laboratories for investigating the evolution of barred disks, only sparse and disparate results have emerged from early studies. In this thesis, we study barred disks in clusters using high-quality data from the Hubble Space Telescope Advanced Camera for Surveys for the moderately-rich cluster Abell 901/902 (characterized by a galaxy number density n~1,000 gal Mpc⁻³) at z~0.165, and of the Coma cluster at z~0.02, the densest cluster (n~10,000 gal Mpc⁻³) in the nearby Universe. We find that the optical bar fraction for bright, early Hubble type disk galaxies does not show a statistically significant variation (within the error bars of ± 10 to 12%) as a function of galaxy environment within the Abell 901/902 cluster, as well as between the Abell 901/902 cluster and the field. Similarly, the optical bar fraction for bright S0 galaxies shows no statistically significant variation (within the error bars of ±10%) between the Virgo, Abell 901/902, and core of the Coma clusters, even though these environments span over an order of magnitude in galaxy number density (n~300 to 10,000 gal Mpc⁻³). We suggest that the S0 bar fraction is not greatly enhanced in denser environments, such as the core of Coma, due to the predominance of high speed encounters over slow ones, the tidal heating of S0 disks, and the low gas content of S0s in rich clusters. / text

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

No description available.

We present new submillimetre images of the dwarf irregular galaxy IC 10, taken with the Submillimeter Bolometer Common-User Array, mounted on the James Clerk Maxwell Telescope. Combining this new data with archival data from the 2MASS survey, ISO, Spitzer IRAC and MIPS, and the VLA, we plot the observed spectral energy distributions from 1.24 μm to 850 μm for two star forming regions within IC 10, namely IC 10 SE and IC 10 NW. The spectral energy distributions were subsequently modelled using a dust model with PAHs, and silicate and graphite dust grain components. This is the first time that well-constrained spectral energy distribution models of two individual regions within IC 10 have been presented. From our results, we find that IC 10 SE and IC 10 NW share the same physical characteristics in most cases, such as the gas-to-dust mass ratio, the mass fraction of PAHs comprising the total dust mass, and the fraction of PAHs that are ionised. The most significant difference is seen in the peak wavelengths of the SEDs, which are ~70 μm and ~45 μm for IC 10 SE and IC 10 NW, respectively. From this we conclude that the primary dust component within IC 10 NW is warmer than that of IC 10 SE, due to the hot young stars at the heart of the star forming region within IC 10 NW having a larger heating effect on the nearby dust than the interstellar radiation field. The similar environments of these two regions lead us to suggest that the star formation taking place within them was triggered by the same starburst, and that both stellar populations evolved together. We also find that IC 10 has physical conditions that are common amongst other low-metallicity, dwarf irregular galaxies, implying that IC 10 does not have an abnormal interstellar medium in these regions. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-09-09 12:20:52.184

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references. / Microfiche. / xiv, 184 leaves, bound ill. 29 cm

Thesis (Ph.D. 1978) from the Department of Mathematical Physics, University of Adelaide.

Thesis (Ph.D) - Swinburne University of Technology, Faculty of Information & Communication Technologies, 2006. / A dissertation presented in fulfilment of the requirements of for the degree of Doctor of Philosophy, Faculty of ICT, Swinburne University of Technology, 2006. Typescript. Bibliography p. 90-99.