April 1, 2009 | 3:30 PM | RI 480 | Astronomy Colloquium A Dustier Universe Than You'd Like Ryan Scranton, UC, Davis
Using galaxies and quasars from the Sloan Digital Sky Survey, we have extended previous work measuring the weak lensing magnification. We can now compare our measurements directly to those made using galaxy-galaxy shear lensing and find that the results agree remarkably well. Our new technique also allows us to make the first measurements of the extended dust halos associated with the galaxies in our sample, detecting a level of intergalactic dust roughly twice that expected from theoretical estimates. At a mean redshift of z ~ 0.35, we find that the dust halos of galaxies extend to Mpc scales, following a power-law density distribution and exhibiting a reddening slope equivalent to that seen in the LMC. From this we infer a smooth halo component to the dust that cannot be accounted for by radially averaging satellite galaxies and find a dust mass density for the universe roughly twice that from previous estimates. Finally, we present some preliminary estimates for the impact of this dustier universe on current and future supernova cosmology measurements.
April 8, 2009 | 3:30 PM | RI 480 | Wednesday colloquium The Radio Background from ARCADE 2 Dale J. Fixsen, University of Maryland
The ARDCADE 2 instrument has measured the absolute temperature at 3-90 GHz, with an open aperture cryogenic instrument observing at balloon altitudes with no windows with an in situ blackbody reference. The radio background is larger than expected with a temperature of 1.2 K at 1 GHz with an index of -2.6. Then CMB temperaure agrees with FIRAS.
April 15, 2009 | 3:30 PM | RI 480 | Astronomy Colloquium Constraining Dark Energy: First Results from the SDSS-II Supernova Survey Josh Frieman, FNAL/University of Chicago
A decade ago, two teams studying distant type Ia supernovae discovered that the expansion of the Universe is speeding up. Since then, supernova surveys from the ground and from space have brought major improvements in the quality and quantity of SN Ia data, confirming the discovery of cosmic acceleration. This talk will focus on early cosmological results from the Sloan Digital Sky Survey-II Supernova Survey, which operated for 9 months in 2005-7, discovering and measuring light curves and spectra for over 500 SNe Ia. I will discuss the observational challenges to determining supernova distances for cosmology and how those challenges are being addressed. These results inform the prospects for using supernovae to obtain improved cosmology measurements from planned and proposed surveys in the future.
April 22, 2009 | 3:30 PM | RI 480 | Wednesday colloquium Dark Stars, or the Effect of Dark Matter on the First Stars Paolo Gondolo, University of Utah
The first stars in the universe may have been powered by dark matter heating rather than nuclear fusion. They were dark matter-powered stars, or for short Dark Stars. The annihilation of weakly interacting massive particles would provide the heating. This talk presents the story of Dark Stars: how they form, how long they might live, and what they might become at the end of their lives.
April 29, 2009 | 3:30 PM | RI 480 | Astronomy Colloquium Empirical Constraints on the Formation and Evolution of Low-Mass Stars and Brown Dwarfs: A Data-Intensive Approach Keivan Stassun, Vanderbilt University
Recent and ongoing large surveys, both from the ground and from space, are enabling new data-intensive approaches to a variety of problems in stellar astrophysics. This talk describes three such projects, each serving as a vignette of a different but complementary mode of data-intensive research into low-mass star formation and evolution. The X10000 Project takes a panchromatic, time-domain approach to study the structures of young stellar coronae in order to understand the role of extreme coronal mass ejections in the angular momentum evolution of young stars. SLoWPoKES takes an ensemble, data-mining approach to extract from the Sloan Digital Sky Survey the largest sample of wide low-mass binaries ever assembled, which can be used to constrain binary formation theory and for refining the fundamental mass-age-activity-rotation-metallicity relations for low-mass stars. The EB Factory project takes a time-domain, data-mining approach to identify rare, but astrophysically very interesting, case studies from among the large numbers of eclipsing binaries being harvested by surveys for transiting exoplanets. We will highlight recent discoveries from this work, and will draw these results together to elucidate the physical interrelationships between stellar rotation, magnetic field generation, and stellar structure during the star-formation process.
May 6, 2009 | 3:30 PM | RI 480 | Wednesday colloquium Early Results from the Fermi Large Area Telescope Gamma-ray Sky Survey Rob Cameron, SLAC/KIPAC
The Fermi Gamma-ray Space Telescope was launched in June 2008. The Large Area Telescope (LAT) instrument on Fermi is designed to study the gamma-ray sky in the energy range from 20 MeV to 300 GeV. The first year of the Fermi mission is devoted to a full sky survey with the LAT, started in August 2008. I will summarize the Fermi mission capabilities and report on the survey progress with details of some interim science results.
May 13, 2009 | 3:30 PM | RI 480 | Astronomy Colloquium Astronomy from Dome A, Antarctica Lifan Wang, Texas A&M University
The Antarctic plateau provides many exciting possibilities for astronomical observations. The next decade may see a significant astronomical buildup on the Antarctic Plateau. Dome A and Dome C are currently the two most promising sites. These high points on the plateau have unique properties for astronomical observations. Two of these arise from the extreme cold: the column density of water vapor is lower than at any other site, thus opening unique windows at infrared and submillimeter wavelengths; and the ambient temperature, and thus the thermal background emission of telescope mirrors, is lower than at any other site. Two more advantages arise from the unique character of the atmospheric turbulence: the atmospheric boundary layer is extremely thin, only tens of meters, which opens the possibility of wide field, high resolution imaging by either adaptive correction of the thin ground layer or by raising the telescope above the boundary layer; the wind speeds at all levels of the atmosphere are low, which is highly favorable for adaptive correction. It will likely be possible to form diFFraction limited images over a good fraction of the sky down to visible light wavelengths three times HST resolution for an 8 m telescope. Dome A, being the highest and coldest point in Antarctica, is especially promising based on the results of recent theoretical models and site surveys. More comprehensive site monitoring should be planned for the next decade. Based on existing data, the site has certain areas of astronomical observations can already be planned with little risks. Wide field near-IR imaging, for example, relies critically on the thermal background and the low temperature at Dome A makes it an ideal site. Another key area is likely to be exoplanet imaging and spectroscopy in the L-band, where the combination of super-diFFraction limited AO correction and the very low thermal background will enable very high contrast imaging at very close inner working angle, for example 0.15 arcsec for an 8 m telescope.
May 20, 2009 | 3:30 PM | RI 480 | Wednesday colloquium Cosmology and Astrophysics with Galaxy Clusters Daisuke Nagai, Yale University
Clusters of galaxies are unique probes of cosmology and astrophysics, promising to provide new insights into both the nature of dark energy and dark matter and the physics of galaxy formation. One of the key challenges facing this approach lies in our understanding of cluster physics and their impact on cluster structure and evolution. In this talk, I will review recent development of theoretical and computational modeling of galaxy cluster formation, with focus on thermodynamic of intracluster medium. Numerical simulations including gas cooling and star formation reproduce global properties of the intracluster medium (ICM) and observable-mass relations with the accuracy of ~10%. I will show that non-thermal processes, such as turbulence, cosmic-rays, and ICM plasma physics, are the dominant sources of systematic uncertainties in the current cluster mass estimate. I will discuss the future prospect for improving our understanding of cluster astrophysics and cosmological constraints with upcoming large-scale cluster surveys.
May 27, 2009 | 3:30 PM | RI 480 | Astronomy Colloquium Lessons from the Nearby Universe about Star Formation in Galaxies Alberto Bolatto, University of Maryland
The study of the relation between gas and star formation in galaxies is a matter of great current interest, and a crucial piece of information in our understanding of galaxy evolution. In order to determine how primordial density fluctuations become observable structures in the present day universe, it is crucial to characterize the processes that drive star formation on galactic scales. In turn, I will argue, this requires considering the creation of the self-gravitating cold molecular phase of the interstellar medium: Giant Molecular Clouds (GMCs). In this talk I will present multi-scale measurements of the relation between gas and star formation in galaxies (the "star formation law"), and discuss our current knowledge of this relation. I will also discuss our new results on dust formation by supernovae, frequently assumed to be the major dust creation pathway in the early universe. The properties of GMCs, the major reservoirs of star-forming gas, play a key role in setting the initial conditions for the formation of stars. I will discuss the results from a comprehensive study of the resolved GMC properties in a number of extragalactic systems, including both normal and dwarf galaxies, and I will contrast the results of the virial and high-resolution far-infrared studies and what they tell use about molecular clouds in primitive galaxies and the relation between gas and the formation of stars.
June 10, 2009 | 3:30 PM | RI 480 | Wednesday colloquium Radio detection of extensive air showers Joerg R Hoerandel, Radboud University Nijmegen
The origin of cosmic rays, among them being the highest energy particles in the Universe is one of the main open questions in Astroparticle Physics. Air showers are induced by interactions of high-energy cosmic rays in the atmosphere. Secondary electrons (and positrons) are deflected in the Earth's magnetic field and emit synchrotron radiation. This radio emission is detected by dipole antennas. The technique has been pioneered by the LOPES experiment, operated in coincidence with the KASCADE-Grande air shower experiment. Radio emission of ultra high-energy cosmic particles offers a number of interesting advantages. Since radio waves suffer no attenuation, radio measurements allow the detection of very distant or highly inclined showers, can be used day and night, and provide a calorimetric measure of the electromagnetic shower component. The LOPES experiment has detected the radio emission from cosmic rays, confirmed the geosynchrotron effect for extensive air showers, and provided a good calibration formula to convert the radio signal into primary particle energy. Future steps will be the installation of a 20 km^2 radio antenna field at the Pierre Auger Observatory to measure the composition of cosmic rays in the energy region between 10^17 and 10^18 eV. In this region a transition from galactic to extra-galactic origin of the particles is expected. Prototype studies are presently conducted on site in Argentina. Future activities also include the use of the LOFAR radio telescope as cosmic-ray detector. The LOFAR telescope is presently constructed in the Netherlands and in Europe as a digital radio interferometer. The present status of the activities is reviewed and the perspectives will be discussed. It is expected that the radio technique will develop into a mature and independent method to detect ultra high-energy cosmic rays within the next decade.
April 3, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar Wandering in the Hyperfine Forest (Presentation given by Jeff McMahon and Eric Switzer) Jeff McMahon, The University of Chicago
There has been much excitement recently about 21 cm radiation as an observable of both the reionization era and large scale structure at redshifts roughly z=1 to z=0. A natural question is whether there are other cosmologically observable hyperfine transitions. In the first part of this research talk, we give an overview of the atomic hyperfine transitions and then restrict to the 8.7 GHz transition of 3He+ as an observable of He+ reionization [Eric Switzer]. In the second half of the talk, we return to the 21 cm emission from galaxies [Jeff McMahon]. There are several proposed mapping experiments to measure the 21 cm emission from galaxies to constrain the scale of baryon acoustic oscillations. We consider an alternative approach of integrating down along a sparse array of sight lines which can be arranged to maximize sensitivity to the BAO scale. These are both active research projects, so questions and criticism are encouraged.
April 10, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar The Galaxy in Gamma Rays: Results from VERITAS Brian Humensky, The University of Chicago
VERITAS, the Very Energetic Radiation Imaging Telescope Array System, is a ground-based observatory for studying nonthermal astrophysics in the gamma-ray band above 100 GeV. The complete four-telescope array has been operating at the Fred Lawrence Whipple Observatory in southern Arizona, USA since the spring of 2007. Observations of galactic sources - including supernova remnants, pulsar wind nebulae, X-ray binaries, and a survey of the Cygnus region - have proven extremely fruitful. Key results include the discovery of VHE emission from the supernova remnant IC 443, studies of the surprisingly variable X-ray binary system LS I +61 303, and the discovery of variability in the unidentified source HESS J0632+057. The Fermi Gamma-ray Space Telescope, launched in June 2008, has opened a new window on gamma-ray astronomy in the complementary band between 100 MeV and 100 GeV. This talk will discuss these early VERITAS results and the interplay between Fermi and VERITAS in the study of galactic gamma-ray sources.
April 17, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar Planck Graca M M S T Rocha, Jet Propulsion Laboratory - Caltech
Planck satellite is designed to image the anisotropies of the Cosmic Background Radiation over the whole sky, with unprecedented sensitivity and angular resolution. It has been selected as a third Medium Sized Mission (M3) of ESA's Horizon 2000 Scientific Programme, and it is today part of its Cosmic Vision Programme. Planck will provide a major source of information relevant to Cosmology and Astrophysics. It will test theories of the early universe and the origin of cosmic structure and will provide surveys of both galactic and extragalactic emission at arcminutes angular resolution. Planck will be launched together with the Herschel satellite. After launch Planck and Hershel will separate and will be placed in different orbits around the second lagrangian point of the Earth-Sun System. In this talk I will give an overview of Planck instrument and its expected science output. With Planck launch imminent (presently scheduled for the 6th of May), we are looking forward to exciting times for CMB cosmologists.
April 24, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar Black Hole Mergers and Electromagnetic Counterparts Bence Kocsis, Institute for Advanced Study
The anticipated detection of the gravitational waves (GWs) by the future Laser Interferometric Space Antenna (LISA) will constitute a milestone for fundamental physics and astrophysics. While the GW signatures themselves will provide a treasure trove of information, if the source can be securely identified in electromagnetic (EM) bands, this would open up entirely new scientific opportunities, to probe fundamental physics, astrophysics, and cosmology. I will describe several mechanisms that might produce EM variability during a SMBH merger. In particular, the binary may produce a roughly periodic variable electromagnetic ?ux, due to the orbital motion prior to coalescence, a transient signal caused by shocks in the circumbinary disk when the SMBH binary recoils and ”shakes” the disk, or a prompt EM flare caused by the viscous dissipation of GWs in the ambient gas. I will discuss whether these time-variable EM signatures may be detectable using a LISA-triggered EM counterpart search campaign.
May 1, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar CMB Lensing - Constraints on Dark Energy and Neutrinos Roland de Putter, UC Berkeley/Berkeley Lab
Weak gravitational lensing of the cosmic microwave background (CMB) by large scale structure along the line of sight shuffles the pattern of temperature and polarization anisotropies on the sky. This makes the CMB sensitive to physics that affects the growth of structure at z=1-4, like massive neutrinos and dark energy. In this talk, I will review how gravitational lensing distorts the CMB power spectra and how the lensing signal can be extracted from the observed anisotropies. I will then discuss prospected constraints from CMB lensing by future probes like Planck and CMBpol on three types of physics beyond standard LCDM: massive neutrinos, ordinary dynamical dark energy and early dark energy. I will also compare the constraining power of two methods for extracting the lensing signal from the CMB: smearing of power spectra vs the optimal quadratic estimator of the lensing potential power spectrum.
May 8, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar Constraining the inflationary paradigm with current and future data Maria Beltran, The University of Chicago
The inflationary paradigm was proposed more than two decades ago. Although a voluminous amount of cosmological data allows us to impose tight constraints on the inflationary mechanism, the model is by no means fixed yet. I will briefly review the current status of our understanding of the inflationary process and what could we expect to learn from future CMB experiments. In particular, I will focus on the possibility that no primordial tensor modes are observed. I will show that, in this case, one could appeal to the curvaton inflationary model and rely in other observables such as the primordial non-Gaussianity or the bounds on the isocurvature contribution to the CMB anisotropies to understand the nature of inflation.
May 15, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar The measurement of Cosmic Ray Electrons from 20 GeV to 1 TeV using the Fermi Large Area Telescope Jonathan F. Ormes, University of Denver
The spectrum of electrons near 1 TeV provides important constraints on models of cosmic ray origin and propagation and has been proposed to indicate a possible signature of dark matter. I will report on the measurement of Cosmic Ray Electrons to 1 TeV using the Fermi Gamma-ray Space Telescope’s Large Area Telescope. In contrast to other measurements to date made on balloons or the shuttle where both systematic and statistical errors can be problematic, these results are based on over 4 M electrons > 20 GeV and are statistically precise. Thus, the measurement is limited by systematic errors. A detailed Monte Carlo simulation of the instrument response to both electrons and protons (and helium), combined with the high statistics, allows the systematic errors to be characterized and understood. The results will be described and compared with the other recently published results from Pamela, ATIC and HESS. The astrophysical implications for cosmic ray propagation, sources, and other interpretations will be discussed.
May 22, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar The Cosmic Microwave Background, Interferometry, and Polarization Jonathan Sievers, CITA
Interferometers have played a major role in observations of the Cosmic Microwave Background. The measurement of fringes rather than total power means that interferometers are resistant to a slew of potential systematics, in particular atmospheric fluctuations larger than the field of view are rejected. They are also well-suited for polarization measurements - because they directly measure the polarized signal, gain fluctuations are relatively unimportant. Their principal drawback has been the high cost of getting large numbers of detectors on the sky. However, recent technological developments have raised the prospects of vastly larger interferometers. We discuss the history and present state of interterferometric measurements of the CMB and present thought on future measurements, particularly of primordial B-mode polarization.
May 29, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar Observational Constraints on Gravitational Wave Recoil Kick Velocities in Supermassive Black Hole Binaries from Radio Galaxies C.C. Teddy Cheung, NASA GSFC
In recent years, general relativity simulations of binary black hole mergers have demonstrated that large 'kicks' due to gravitational wave radiation recoil are possible. An observable manifestation of this phenomena would be a displacement of the resultant active nucleus from its parent host galaxy. We test this interesting possibility with astrometric radio and optical measurements of a large sample of radio galaxies, focusing in particular on the class of restarting sources with so-called 'double-double' and 'X'-shaped morphologies. The unusual morphologies of the restarting sources suggest a relatively recent merger, and such angular offset measurements place useful observational constraints on possible kick velocities resulting from super-massive black hole binary mergers.
June 5, 2009 | 12:00 PM | LASR Conference Room | Friday noon seminar New Results on CMB Polarization from BICEP and QUaD Clem Pryke, The University of Chicago
I will start with a brief update on the latest results from QUaD. I will then move on to the BICEP1 instrument, it's calibration and analysis, and present ground breaking new results on B-mode polarization in the crucial few degree angular scale range where the inflationary signal is expected to peak. I will finish by describing the on-going BICEP2/Keck-Array program which will produce still more sensitive results within a few years.
April 21, 2009 | 3:30 PM | LASR Conference Room | Special seminar Baryon Acoustic Oscillations with Luminous Red Galaxies and the PAU Survey Enrique Gaztanaga, Instituto de Ciencias del Espacio, Barcelona
In the first part of the talk, I will present new results on the clustering of luminous red galaxies (LRG) along and transverse to the line-of- sight (LOS) in the SDSS survey. We use these measurements to study the growth of structure and the pairwise velocity distribution. We find a significant detection of baryon acoustic oscillations (BAO) along the LOS direction, providing a direct measure of the rate of explansion of the universe. These topics are the main drivers for the Physics of the Accelerating Universe (PAU) Survey, which I describe in the second part of the talk. PAU will carry out a large photometric survey with a 3 sq. deg. field of view camera on a new, dedicated 2.5m telescope in Spain. PAU will use a system of 40 narrow filters covering the wavelength range from 4000A to 8000A, supplemented by broad-band filters similar to those in SDSS and DES. We expect to measure positions and redshifts for over 14 million LRGs over the SDSS survey area in the redshift interval 0.1 < z < 0.9, with a precision of 0.3%, i.e., sigma(z) < 0.003(1+z). Such a survey can measure the dark-energy equation of state parameter w with 5% accuracy and can determine its time derivative when combined with other measurements. PAU will be a Terapixel Redshift Survey, providing integral field low-resolution spectroscopy for a large fraction of the sky, with tremendous legacy potential for astrophysics.
April 7, 2009 | 12:00 PM | RI 180 | Special Seminar Accretion, Feedback, and Tidal Interaction Mechanisms in our Local Neighborhood Nicolas Lehner, University of Notre Dame
Characterizing the infall and outflow of gas and metals in galaxies is crucial for understanding the evolution of galaxies and the intergalactic medium. The study of these phenomena in local galaxies provides the most robust diagnostic tests for models of tidal interaction, galactic winds, and accretion of primordial material onto galaxies, which are important for piecing together the history of matter and metals in the Universe. The Magellanic System with its high-velocity complexes connected to the Magellanic Clouds provides a laboratory where the techniques of gas-phase absorption line spectroscopy can be used to study the gas toward many individual stars and QSOs. Here I will present results on the Magellanic Clouds that have changed our views of these galaxies.
April 29, 2009 | 11:00 AM | RI 480 | Special Seminar Enhancing Diversity in Astronomy in the Coming Decade Keivan Stassun, Vanderbilt University
We briefly review the current status of ethnic minorities in the physical sciences: The underrepresentation of Black-, Hispanic-, and Native-Americans is an order of magnitude problem. We then describe in detail the Fisk-Vanderbilt Masters-to-PhD Bridge program as a successful model for effective partnerships with minority-serving institutions toward addressing this problem. The program couples targeted recruitment with active retention strategies, and is built upon a clearly defined structure that is flexible enough to address individual student needs while maintaining clearly communicated baseline standards for student performance. Students are deliberately prepared to transition into the Vanderbilt PhD program through active involvement in research experiences with future PhD advisers, coursework that demonstrates competency in core PhD subject areas, and frequent interactions with joint mentoring committees. Since 2004 the program has admitted 31 underrepresented minority students (60% female), with a retention rate of 94%. Recent research indicates that minority students are 50% more likely than non-minority students to seek a Masters degree en route to the PhD. In essence, the Bridge program builds upon this increasingly important pathway, with a dedicated mentoring process designed to ensure that the Masters-to-PhD transition is a successful one. Finally, we discuss larger demographic trends among minorities in higher education, and suggest promising approaches for significantly broadening participation of minorities in the coming decade