Not only does cold hydrogen gas swirl with stars around the centre of a spiral galaxy, forming a disk, but gas filaments stretch way from the disk and clouds are distributed throughout a galaxy's extended halo. This halo contains the elusive dark matter that makes up 90% of the material of the universe. Given that a typical galaxy contains hundreds of billions of stars, a galaxy's original cold gas reservoir should have been drastically depleted as this gas converted into stars over its several billion year history. Why do spiral galaxies still have significant amounts of gas in their disks and continue to form stars? Since galaxies are distributed throughout the universe in a web-like structure, could gas be flowing from this so-called Cosmic Web into individual galaxies? Does the distribution of dark matter in an individual galaxy, as well as throughout this web, influence this putative flow? My proposed research tackles these questions by studying the MOTION of the cold hydrogen gas in 3 dimensional datasets. These `data cubes' are generated by collecting an image per frequency channel using a radio telescope's receiver. We use an unconventional genetic algorithm to `ferret out' models that accurately fit the 3-D gas disk of a galaxy in such data cubes. We harness this algorithm using our powerful software program, GalAPAGOS (also known as MantaH), developed only in Canada at the University of Manitoba. GalAPAGOS characterizes the orbit of the gas in a galaxy's disk and consequently the gravitational effect of an individual galaxy's dark matter halo. Using our sophisticated model disk as a mask, we can also isolate the movement of the halo clouds to ascertain whether their motion supports the hypothesis that a galaxy's gas reservoir is replenished from the Cosmic Web. Additionally we have characterized the orbit of gas disks to develop a preliminary kinematic classification scheme for almost all observed nearby spiral galaxies that are not interacting with companion galaxies (~80 galaxies). Since our software is semi-automatic it will be highly efficient for analyzing the thousands of galaxies collected by the big budget state-of-the-art radio telescopes (e.g. ASKAP & MeerKAT) currently under-construction for multinational research consortiums of which I am a member. To improve our classification scheme, and to make predictions about galaxies that can be tested on these upcoming observations, my personel and I begin by applying our technical approach to artificial galaxies generated in cosmological computer simulations. These simulations start with the Big Bang and using physical equations evolve the universe to present times. The simulations of our American and Australian collaborators include gas inflow from the Cosmic Web onto galaxies and the characteristics of the simulated galaxies are fully known. Therefore we can use them to predict observational signatures of the interplay between cold gas structures within dark matter halos, halo characteristics, and galaxy disks, to test if cosmic flow is a relevant mode of gas accretion leading to on-going star formation in spiral galaxies. These predictions will impact international colleagues' research into DM halo structure as well as alternative gravitational theories. Additionally our classification scheme will enable cosmologists to characterize primordial galaxies to assess their origins.
There are 2 possibilities for projects. The first involves extending the capability's of GalAPAGOS to include very cold gas (carbon monoxide) so that the kinematics of galaxies can be investigated using data from the Atacama Large Millimetre/submillimetre Array. ALMA is currently the world's premier telescope - more projects are requested on ALMA than on any other. It attains the same detail as the Hubble Space Telescope, allowing us to probe close to galaxies' central black holes. The candidate for this project will be an author on a paper that traces the orbital motions in the inner part of galaxies and show how ALMA helps constrain the characteristics of dark matter halos.
For the second project candidate will be lead author on a paper investigating whether our classification scheme, derived from limited observational data, can be reproduced using 100's of artificial galaxies extracted from cosmological simulations. Since the simulated galaxies have specified characteristics, correlations between galaxy features and kinematic parameters can be assessed for their potential predictive power. To accomplish sophisticated modelling of galaxies, my team develops and implements a novel software code called GalAPAGOS and creates visualization techniques for both research and public outreach endeavours. This candidate will demonstrate that GalAPAGOS is more advantageous than other routines for studies using world-class radio telescopes ASKAP and MeerKAT data - these telescopes are critical precursors to the next extreme advance in radio astronomy, the Square Kilometre Array (SKA). The candidate will also contribute to a paper on an observed galaxy with a peculiar shape, demonstrating that GalAPAGOS has the unique ability to model challenging galaxies.
In both projects cutting-edge computational experience will be acquired. The blend of theoretical astrophysics, computational physics, astronomical data and analysis, and visualization offer rich, interdisciplinary opportunities necessary for success in contemporary endeavours in astronomy. These activities will train the candidate for employment at forefront research institutions.
Requirements include a B.Sc.in Physics or Physics & Astronomy, grades in good standing, computational experience (GalAPAGOS is developed using Matlab), and a high TOEFL score (if from overseas). Note that an outstanding student can convert to a PhD program after roughly the first year of study.
If you are a suitable and interested candidate please fill out the enquiry form and contact Dr. English.
The image shows a starless, hydrogen Vela Cloud in central region of the NGC 3256 Group of galaxies. Superimposed on the star field is velocity field. Bluer colours indicate blue-shift and redder colours correspond to red-shifted gas. Thus one can see the rotational signatures of the galaxies and can note that the Vela Cloud does not appear to be rotating.