University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Prowse Room

Fall 2014 & Spring 2015 Schedule

September 12 Atomic and Ionized Hydrogen Gas at the Disk-Halo Interface in Spiral Galaxies
Rene Walterbos (New Mexico State University)

Observations over the past two decades have provided ample evidence for thick layers of HI and diffuse ionized gas extending sometimes far above the midplane of galaxies into their halos. A few nearby galaxies, including the Milky Way also show evidence for a distribution of HI clouds and filaments further into the halo. Some of these features may be explained by galactic fountains, a cyclical process of gas outflow and inflow driven by star formation in the disk. Accretion of gas from the IGM and from tidal interactions is also called for to explain some of the larger scale phenomena. The kinematic signature of the gas at the disk-halo interface may provide information on the origin of the gas. I will describe some recent results on the kinematics of HI from deep observations with the WSRT and VLA radio telescopes of a sample of nearby disk galaxies, as part of the HALOGAS project, and from deep multi-slit spectroscopy of ionized gas in edge-on galaxies with the ARC 3.5m telescope. A general result is a decrease in rotational velocity of gas with height above the disk. The sense of the lag is as predicted by galactic fountain models, though its magnitude is far larger than simple models would predict. In general, few galaxies show strong evidence for accretion of cool gas, and the bulk of IGM inflow predicted to exist remains as of yet undetected.

September 19 Title, TBD
Paul Butler (Carnegie Institute of Washington)

Modern science began with Copernicus speculating that the Earth is a planet and that all the planets orbit the Sun. Bruno followed up by speculating that the Sun is a star, that other stars have planets, and other planets are inhabited by life. For this and other heresies, Bruno was burned at the stake in a public square in Rome in 1600. Astronomy and extrasolar planets were a really hot field at the time. Over the past 20 years more than a thousand extrasolar planets have been found, first from ground-based precision Doppler and photometric transit surveys, and more recently by the Kepler space mission. We have concentrated on building precise Doppler systems to survey the nearest stars. Our systems at Lick, Keck, AAT, and Magellan have found hundreds of planets, including 5 of the first six planets, the first saturn-mass planet, the first neptune-mass planet, the first terrestrial mass planet, and the first multiple planet system. We are currently focusing our attention on new custom built "R4" echelle spectrometers designed for Iodine cells, which are yielding 1 m/s precision. These spectrometers have a footprint about the size of a ping pong table, allowing for temperature stabilization, yet deliver higher resolution and dispersion than the much larger classic echelle spectometers, such as the Lick Hamilton, the AAT UCLES, and the Keck HIRES. The two working examples, PFS on Magellan, and the Levy spectrometer on the 2.4-m APF, cost about US$2M each. They do not use fibers or scrambling, and have throughput of 20 to 30%, a factor of 2 to 4 better than classic echelles. These spectrometers will lead to the discovery of many terrestrial mass and potentially habitable planets over the next decade.

September 23 Magnetic Materials in Medicine: Applications in Diagnosis, Management, and the Treatment of Disease
Tim St Pierre (University of Western Australia)

Scientists working in the field of magnetic materials are increasingly focusing their attention on new applications of magnetic detection and magnetic transduction techniques in the biomedical sciences. Iron is a key functional element in the human body and surpasses all other naturally occurring elements in the body in terms of both the variety and magnitudes of its magnetic states. In many diseases, the quantity and the magnetic state of iron are altered by the disease. Hence, detecting and measuring the magnetic properties of the iron in vivo or in samples of body fluids can give insights into the state of health of a human subject. Example applications include assessing the risk of organ damage in hereditary hemochromatosis [1], determining the dose of iron chelator drugs required for patients with thalassemia [2], and identifying infectious forms of the malarial parasite in finger-prick blood samples [3]. Scientists are also working on the development of synthetic magnetic particles that can be injected into the human body for the diagnosis and treatment of disease. The particles used are generally in the size range of 10 to 100 nm. They can be used to enhance the contrast in magnetic resonance images to help identify tumors in tissue [4], to act as local heat sources to treat cancer [5], and to carry, concentrate, and release drugs more specifically than drugs without a magnetic carrier [6]. In this presentation, the physical and chemical principles behind these biomedical applications and their impact on medicine will presented at a level suitable for a generalist audience.

October 31 High redshift quasars in VIKING; Progress and Science
Joseph Findlay (University of Wyoming)

Luminous high redshift quasars are versatile probes of the early Universe, setting constraints on the seeding and growth of the first population of massive black holes, gas phase metallicity evolution, cosmic reionization and much more besides! Quasars at the highest redshifts are extremely rare, searches must be conducted over extremely wide fields and moderate depths. Since 2012 we have been conducting a followup campaign on z>6.5 quasar candidates selected in the ESO public VIKING survey. In this talk I will discuss selection techniques, present the first spectroscopically confirmed sources and discuss ongoing science with the sample.

November 14 Evolution of quasars at high redshift from large optical surveys
Ian McGreer (Unversity of Arizona/Steward Observatory)

A wealth of data indicates that massive galaxies universally harbor supermassive black holes at their centers. Most of the mass in these black holes accumulated during relatively brief quasar phases, where the luminosity generated by the black hole accretion exceeds that of the total starlight from the galaxy. Surveys of quasars at optical wavelengths are especially efficient at tracing the growth of supermassive black holes; we are now approaching a million quasars with spectroscopic redshifts, and observations reach to systems formed within the first billion years of the universe. The improved statistics provided by recent surveys show that quasars sharply decline in number density at z>3, as known for decades, but more surprisingly that the characteristic luminosity (the break in the luminosity function) evolves to continually higher luminosities out to z~6. This steady shift to more extreme systems suggests that the most massive black holes formed early and grew rapidly. I will discuss some limitations of current studies of quasar demographics and how these can be addressed with simulations of quasar properties and with observations that break degeneracies in theoretical models of quasar activity.

November 21 Generation of Pure Spin Currents using Magnetic Insulators
Mingzhong Wu (Colorado State University)

Pure spin currents are very promising for information transfer and processing for future low-power "green" electronics. There is a strong interest in using yttrium iron garnet (YIG) to generate pure spin currents, either via spin pumping or the spin Seebeck effect (SSE). This interest originates from the fact that the damping in YIG materials is lower than in any other known magnetic materials. The development of YIG-based, nanoscale spin batteries, however, demands YIG films that have a thickness in the nanometer range and at the same time exhibit low damping similar to single-crystal YIG materials. The growth of such YIG films will be discussed in the first part of this presentation. The second part will report on the exploration of optimal regimes for spin-wave spin pumping using YIG thin films, which will provide significant implication for the future development of high-efficient spin batteries. There are three main types of magnetic insulators: spinels, garnets, and hexagonal ferrites, with the first two being usually classified as soft magnetic materials and the third as hard. Previous work has demonstrated the SSE in "soft" spinels and garnets, but not in "hard" hexagonal ferrites. In the third part of this presentation, the generation of pure spin currents via the SSE in a self-biased hexagonal ferrite thin film will be reported. This work demonstrates a spin battery that requires neither a magnetic field nor a microwave source nor a heating/cooling device, but light only.

February 6 Title, TBD
Kevin France (CU Boulder)

Abstract, TBD

February 20 Title, TBD
Kris Beckwith (Tech-X Corporation)

Abstract, TBD

April 10 Title, TBD
Greg Rudnick (Kansas)

Abstract, TBD

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006 Spring 2007 Fall 2007 Spring 2008 2008-09 2009-10 2010-11 2011-12 2012-13 2013-14
Contact for program information: Adam Myers