A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies

CO and HI velocity fields of seven nearby spiral galaxies, derived from radio-interferometric observations, are decomposed into Fourier components whose radial variation is used to search for evidence of radial gas flows. Additional information provided by optical or near-infrared isophotes is also considered, including the relationship between the morphological and kinematic position angles. To assist in interpreting the data, we present detailed modeling that demonstrates the effects of bar streaming, inflow, and a warp on the observed Fourier components. We find in all of the galaxies evidence for either elliptical streaming or a warped disk over some range in radius, with deviations from pure circular rotation at the level of ~20-60 km/s. Evidence for kinematic warps is observed in several cases well inside R_{25}. No unambiguous evidence for radial inflows is seen in any of the seven galaxies, and we are able to place an upper limit of ~5-10 km/s (3-5% of the circular speed) on the magnitude of any radial inflow in the inner regions of NGC 4414, 5033 and 5055. We conclude that the inherent non-axisymmetry of spiral galaxies is the greatest limitation to the direct detection of radial inflows.Comment: 22 emulateapj pages with bitmapped colour figures, to appear in ApJ (April 2004). For full resolution figures go to http://www.atnf.csiro.au/people/twong/preprints

Distance Estimation in Cosmology

In this paper we outline the framework of mathematical statistics with which one may study the properties of galaxy distance estimators. We describe, within this framework, how one may formulate the problem of distance estimation as a Bayesian inference problem, and highlight the crucial question of how one incorporates prior information in this approach. We contrast the Bayesian approach with the classical `frequentist' treatment of parameter estimation, and illustrate -- with the simple example of estimating the distance to a single galaxy in a redshift survey -- how one can obtain a significantly different result in the two cases. We also examine some examples of a Bayesian treatment of distance estimation -- involving the definition of Malmquist corrections -- which have been applied in recent literature, and discuss the validity of the assumptions on which such treatments have been based.Comment: Plain Latex version 3.1, 18 pages + 2 figures, `Vistas in Astronomy' in pres

Chemo-spectrophotometric evolution of spiral galaxies: I. The model and the Milky Way

The chemical and spectro-photometric evolution of spiral galaxies is investigated with detailed models, making use of up-to-date ingredients (like metallicity dependent stellar properties) and a prescription for the star formation rate (SFR) justified both empirically and theoretically. As a first application, the model is used to describe the evolution of the Milky Way. The role of the adopted scheme of disk formation (``inside-out'') in shaping the various chemical and colour profiles is investigated, as well as the role of extinction. It is shown that the solar neighborhood does not evolve as the Milky Way as a whole and that one-zone models with a non-linear SFR prescription cannot be used to study the evolution of our Galaxy. Our model average SFR is shown to match well observations of external spirals.Comment: 21 pages, 10 figures, accepted in MNRA

Consciousness in the Universe

So far we can identify at least three concepts within modern cosmology that bring into debate the question of consciousness in the universe: 1) Fine Tuning; 2) The Anthropic Principle and 3) The Multiverse. This does not exclude the question of the role of observer (i.e. consciousness) in cosmology as developed within Quantum Physics: we observe the universe through quanta and any breakthrough in understanding the origin and nature of the universe will come only through a quantum theory of gravity […

The evolution of galactic discs with a star formation threshold

SIGLEAvailable from British Library Document Supply Centre- DSC:DXN002432 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Thresholds on star formation and the chemical evolution of galactic discs: cosmochronology and the age of the galaxy

In this paper we analyse different chronometers based on the models of chemical evolution developed in Chamcham, Pitts & Tayler (1993; hereafter CPT) and Chamcham & Tayler (1994; hereafter CT). In those papers we discussed the ability of our models to reproduce the observed G-dwarf distribution in the solar neighbourhood, age-metallicity relation and radial chemical abundance gradients. We now examine their response to the predictions of cosmochronology. We use the recent productio

The philosophy of cosmology

Following a long-term international collaboration between leaders in cosmology and the philosophy of science, this volume addresses foundational questions at the limit of science across these disciplines, questions raised by observational and theoretical progress in modern cosmology. Space missions have mapped the Universe up to its early instants, opening up questions on what came before the Big Bang, the nature of space and time, and the quantum origin of the Universe. As the foundational volume of an emerging academic discipline, experts from relevant fields lay out the fundamental problems of contemporary cosmology and explore the routes toward finding possible solutions. Written for graduates and researchers in physics and philosophy, particular efforts are made to inform academics from other fields, as well as the educated public, who wish to understand our modern vision of the Universe, related philosophical questions, and the significant impacts on scientific methodology