Dr Tully will continue his program of determining distances to nearby disk galaxies, using a relation between galaxy rotation speed and luminosity that has become known as the Tully-Fisher relation. He will measure luminosities from the new deep and uniform imaging surveys Panstarrs and SkyMapper, in the northern and southern sky respectively. He will find rotation speeds from the line-widths of neutral hydrogen emission measured at the Arecibo, GreenBank and Parkes radio telescopes. The immediate tasks are to tie the photometry from the new surveys into his earlier measurements, and to complete 3 neutral hydrogen surveys now in progress. Dr Tully will continue to expand his Extragalactic Distance Database, which brings together the diverse information needed for distance determinations and allows these to be put onto a common scale. The database now contains information for 50,000 galaxies, and is available on the web.
A graduate student will be trained through involvement in the research. An enlarged Extragalactic Distance Database will be a resource both for the astronomical community and for public outreach. Earlier versions have been used to produce 3-D animations of the local distribution of galaxies, planetarium programs, and interactive software available through the American Museum of Natural History. Dr Tully will work with the SkySkan digital planetarium manufacturer and the Imiloa Astronomy Center to produce future 3-D visualizations.
PI: R. Brent Tully, University of Hawaii The measurement of distances to galaxies is a fundamental problem in astronomy. At the most basic level we derive estimates of the size and age of the universe by constraining the parameters of Hubble’s Law, the correlation between distances and velocities due to cosmic expansion. As these parameters are known with increasing accuracy we turn attention to deviations from the cosmic expansion. These departures, called peculiar velocities, are due to gravitational perturbations caused by irregularities in the distribution of matter. Over the age of the universe, these irregularities become more pronounced as matter gathers in clusters and filaments and is depleted in voids. The primary goals of this program are to map peculiar velocities in the nearby part of the universe, make inferences about the current distribution of matter, project the current configuration back to the initial conditions near the beginning of time, use this information as the starting point for computer simulations, and finally evaluate the degree of agreement between a simulation once it reaches the current epoch and the observed characteristics of the local region. The initial ingredient in this thread is distances to galaxies. For a detailed three dimensional map of the mass distribution we need distances to thousands of galaxies, all over the sky, and extending to a distance of order 300 million light years to encompass the range of suspected flows. The methodology currently most suited to address this problem is based on the correlation between the luminosity of a galaxy and the rate of rotation: the Tully-Fisher Relation. There has been a revival of interest in this method because of two technical advances. One critical requirement is a measure of rotation rate, inferred from the width of the neutral Hydrogen spectral line emitted in the radio domain. The Arecibo and Green Bank radio telescopes provide capabilities that have enabled the acquisition of over 10,000 good spectra, now analyzed and publicly available at the project web site. The other requirement is a measure of a galaxy’s luminosity. The initial intent of the program was to obtain this information with the Pan-STARRS facility. There have been delays that have made it unfeasible to use Pan-STARRS data on a time scale commensurate with the period of the award. Fortunately, Spitzer Space Telescope is providing photometry of exquisite quality that is fully adequate. Material from that source is being analyzed and made available to the community through our web site. Four refereed papers give descriptions of the observing campaigns involving the rotation rate measurements with radio telescopes and the ground and space imaging to obtain luminosities. Four more refereed papers describe the steps taken to get galaxy distances, culminating in determinations of the Hubble Constant, the cosmic expansion rate. Our current preferred value for the Hubble Constant is H0 = 75.2+/-3.0 km/s/Mpc. Two further papers describe theoretical steps toward recovery of the local field of peculiar velocities and the inferred distribution of matter.
