September 27, 2006 | 3:30 PM | RI 480 | Wednesday colloquium Type Ia Supernovae from the CFHT Legacy Survey Eric Aubourg, APC Paris / Princeton University
The Supernovae Legacy Survey aims at discovering and spectroscopically identifying 700 type-Ia SN during its five years of operations at CFHT in Hawaii. I will present the survey and the current constraints on matter and energy content of the Universe and on the dark energy equation of state parameter. I will focus on how we plan to increase the expected number of SN to about 1000 using an offline analysis and discuss perspectives of the survey.
October 4, 2006 | 3:30 PM | RI 480 | Astronomy Colloquium Searching for protoplanetary fragments in the Sloan Digital Sky Survey Geza Gyuk, Adler Planetarium
The main asteroid belt represents a significant repository of material left over from the formation of the terrestrial planets. However, the formation and dynamical history of the asteroid belt is complicated, with a significant fraction of asteroids having undergone varying degrees of mechanical and chemical processing. One very important such mechanism is the formation and subsequent disruption of large planetesimals thought to have occured in the early Solar System. Among the most highly processed asteroids are the Vtype. V-type asteroids exhibit absorption bands characteristic of a basaltic (i.e. volcanic) composition, indicating an origin on the crust of large differentiated parent bodies. Until recently all known V-type asteroids were dynamically and compositionally consistent with being fragments of 4 Vesta, the second largest of the asteroids. This talk describes a search for new V-type asteroids, dynamically independent of Vesta, using the Sloan Digital Sky Survey dataset and follow-up observations from Apache Point Observatory. The discovery of new independent V-type asteroids will give us important insights into the timing and processes involved in the formation of planets.
October 11, 2006 | 3:30 PM | RI 480 | Wednesday colloquium Massive Black Holes from Early Times to the Present Marta Volonteri, Northwestern University
I'll discuss models for the hierarchical growth of supermassive black holes, feeding pregalactic black hole seeds. Mergers and dynamical interactions, as well as their implications, will be critically addressed. I'll also discuss the constraints on the early evolution of the black holes required by the observations of z=6 quasars.
October 18, 2006 | 3:30 PM | RI 480 | Astronomy Colloquium Optically Selected Galaxy Clusters: Update 2006 Michael Gladders, The University of Chicago
The Red-Sequence Cluster Surveys (RCS-1, now complete, and RCS-2, ongoing) are a pair of large optical surveys comprising about 1100 square degrees of imaging, designed to find clusters to redshifts beyond one. I will present a number of recent results from these surveys, including the cosmological analysis of RCS-1, and new results on strong lensing in RCS-2. Additionally I will discuss the SDSS cluster catalog, and the future of cluster research within the SDSS.
October 25, 2006 | 3:30 PM | RI 480 | Wednesday colloquium The Origin of Spheroidal Galaxies Sandy Faber, University of California, Santa Cruz
For decades, the standard paradigm for spheroidal galaxy formation was the monolithic collapse theory, in which spheroids collapsed gravitationally in bulk and formed all their stars at very high redshift. This talk will examine evidence that has accumulated over the past year that suggests an extended formation period for spheroidal systems, with many of them forming rather recently via the quenching of blue, star-forming galaxies AFTER z = 1. The mechanism for this quenching is not well understood, but it might be feedback from active black holes. If true, the symbiosis is complete in that the galaxy gives birth to the black hole, but the black hole eventually determines the star-formation history of the galaxy.
November 1, 2006 | 3:30 PM | RI 480 | Astronomy Colloquium High Resolution Radio Cosmology Near and Far Brian Mason, NRAO
Measurements of the angular power spectrum of temperature anisotropies in the Microwave Background strongly support a model in which "primordial" energy density fluctuations generated by inflation-- modified mainly by simple gravity-driven evolutionary processes-- grow to form the structures seen today. While the last scattering surface itself appears to be well-explained by a simple physical picture, important questions remain about the subsequent evolution of large scale structures. For example: what is the state of the present-day mass density field, and where are the baryons? I will discuss two projects with the Green Bank Telescope which address these questions: 30 GHz discrete source observations undertaken to improve the precision of arcminute-scale CMB measurements; and a search for the long millimeter-wave hyperfine transitions of metal ions. I will also briefly describe recent first-light observations with the GBT at 90 GHz and related science prospects in this waveband.
November 8, 2006 | 3:30 PM | RI 480 | Wednesday colloquium Neutrino Telescopes and Their Mission Teresa Montaruli, University of Wisconsin, Madison
The current generation of neutrino telescopes, such as AMANDA and Baikal, has proved that the neutrino measurement is feasible using natural gigantic radiators, such as the polar ice and lake deep water. The cubic kilometer scale detectors are becoming a reality with IceCube being built at the South Pole. Sea water is a critical environment but European collaborations are proving that detectors can operate with good angular resolution, but with larger optical background induced by bioluminescence and potassium 40. I will discuss what could be the most interesting signatures for neutrino telescopes, which could be the astrophysical impact of observations and which are the performances of existing and under construction experiments.
November 15, 2006 | 3:30 PM | RI 480 | Astronomy Colloquium New Challenges in Astrophysical Particle Acceleration Roger Blandford, Stanford/KIPAC
It is nearly a century since Victor Hess understood the nature of GeV cosmic radiation and over sixty years since Pierre Auger demonstrated the presence of PeV particles. The last decade has seen detailed studies of the energy frontier just below a ZeV. In addition imaging of supernova remnants and extragalactic jets by Chandra X-ray Observatory and H.E.S.S. has allowed us to explore astrophysical acceleration sites in detail. High Mach number shock fronts are confirmed as powerful accelerators and it now appears that they also amplify magnetic field and create PeV particles. The manner by which this happens will be discussed. PeV electron acceleration in relativistic jets requires a different mechanism and some possibilities will be explained. Candidate "ZeVatrons" will be reviewed. Finally, prospects for GLAST, which is due for launch next Fall, will be described.
November 29, 2006 | 3:30 PM | RI 480 | Wednesday colloquium Mergers of Massive Galaxies, Central Black Holes, and Dark Matter Halos Chung-Pei Ma, University of California, Berkeley
While mergers of gas-rich disk galaxies are thought to lead to the formation of elliptical galaxies, merging of elliptical galaxies is a potentially important process for building up the most massive galaxies and their central black holes in the low-redshift universe. I will discuss results of simulations of these mergers and the dynamical interplay among stars, dark matter, and black holes in forming the global as well as central properties of massive galaxies. New results from recent analyses of SDSS luminous galaxies find similar trends as seen in the simulations. I will also discuss recent work on understanding the mergers of dark matter halos and the halo mass function using the Smoluchowski coagulation equation.
December 6, 2006 | 3:30 PM | RI 480 | Astronomy Colloquium The Swift Observatory and High Energy Emission from GRB Afterglows Abe Falcone, Pennsylvania State
Swift was launched 2004 November 20. Since that time, the Burst Alert Telescope has detected approximately 2 gamma ray bursts (GRBs) per week, and the pointed instruments, including the X-ray Telescope and the Ultraviolet Optical Telescope, have slewed to a large fraction of these bursts with unprecedented speed. The prompt observation of GRB positions has allowed the X-ray telescope to study GRB afterglows at times that are several orders of magnitude earlier than past observations. Many exciting results have emerged, including X-ray afterglow detections of multiple short-hard bursts, ubiquitous flares at late times (100-10000 s) which imply delayed sporadic internal engine activity, a new canonical afterglow light curve that includes the transition from the prompt emission and multiple breaks in the power law-decay slope, very high redshift afterglow measurements, as well as other new results. A summary of these recent observations and their implications will be discussed, with particular emphasis on the emergence of new phenomena in the early X-ray afterglows of long bursts.
December 13, 2006 | 3:30 PM | RI 480 | Wednesday colloquium Mapping Dark Matter and Dark Energy Using Gravitational Lensing Priya Natarajan, Yale University
Results will be presented on the detailed distribution of dark matter and implications for the nature of dark matter using gravitational lensing of background sources by massive foreground clusters. Strong lensing arcs offer a unique probe of dark energy as well, and I will discuss the utility and feasibility of this technique.
September 29, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar The Photometric Properties of the Most Massive, High-Redshift Galaxies Brant Robertson, KICP
The presence of massive galaxies at high-redshifts (z>7) places constraints on hierarchical scenarios for the cosmological formation of structure. By combining high-resolution hydrodynamical simulations of the hierarchical formation of a redshift z~6 quasar, stellar population synthesis models, prescriptions for interstellar and intergalactic absorption, and the photometric response of modern telescopes, we calculate the observable properties of quasar progenitors at high-redshifts. The rapidly star-forming progenitors of z~6 quasars should be detectable using pre-existing photometric selection techniques like those used to identify distant galaxies in the Hubble Ultra Deep Field, but their low number densities will likely require future surveys of large portions of the sky.
October 6, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar Dark Matter in the Neutrino Sector: Sterile Neutrinos Kevork Abazajian, UMD College Park
Hidden in the neutrino sector may be one or more fermions with no standard model interactions that nonetheless couple to neutrinos via their mass generation mechanism, namely sterile neutrinos. Such a particle may be the dark matter, produced in the early universe through matter-suppressed neutrino mixing or matter-enhanced resonant mixing. I will overview the kinetics of relativistic mixed neutrinos in dense environments, and will specify with sterile neutrino dark matter production in the early universe. I will discuss how this candidate alters cosmological structure formation and the resulting constraints from observed cosmological matter clustering. In addition, I discuss how this candidate may be detected by X-ray telescopes, as well as current constraints from X-ray observations.
October 13, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar Can We See Gravitational Waves from the End of Inflation? Eugene Lim, Yale University
We show that, generically, the process of pre/reheating at the end of inflation is potentially a strong source of gravitational waves. We demonstrate numerically that, for a wide class of simple inflationary models, the gravitational wave energy density produced by such processes can be up to 5 orders of magnitude larger than the most optimistic predictions of the usual primordial gravitational wave spectra. This spectrum is scale-dependent, with its peak frequency inversely proportional to the square root of the scale of inflation. We show that for low scale inflation, this power spectrum is potentially detectable by the next generation GW detectors such as LIGO II.
October 27, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar The XENON10 Dark Matter Search and the Promise of Noble Liquids for a Very Large Scale Dark Matter Experiment Tom Shutt, Case Western Reserve University
Current searches for WIMP dark matter, led by the CDMSII experiment, are entering an exciting regime of probing the range of models predicted by supersymmetry. However a full test of the WIMP hypothesis will require a scale up from current experiments at the kg scale to experiments at the ton scale or beyond. Liquid noble gasses are a particularly attractive option, and their properties for dark matter detection are only now beginning to be understood. I will review the status and promise of liquid noble gas-based detectors, report on the status of the XENON10, which has begun underground operations, and discuss the prospects for a truly large-scale dark matter search, particularly within the context of DUSEL (Deep Underground Science and Engineering Laboratory).
November 3, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar Motion of Satellites and Structure of Outer Parts of Galaxies Anatoly Klypin, New Mexico State University
I will discuss results on the distribution of mass in galaxies as measured by the motion of satellites using SDSS. Updated database of SDSS and improved statistical methods allow us to measure the three key properties of the satellites around galaxies: the rms velocity, the shape of line-of-sight distribution, and the angular distribution of the satellites. Using these results, I will put strict constraints the LCDM model and on MOND. The LCDM fits the data remarkably well. This extends the success of the standard model from magaparsecs down to 50kpc. MOND has a unique prediction on those scales, which I will describe in my talk.
November 10, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar Shooting the Moon: Getting Serious About Gravity Tom Murphy, University of California, San Diego
The fundamental incompatibility of quantum mechanics with general relativity together with our well-quantified ignorance of large-scale gravity (dark energy, dark matter) strongly suggests that we intensify our tests of gravity. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is a new project that will bring about order-of-magnitude improvements in testing several fundamental aspects of gravity. Using a 3.5 meter telescope to bounce laser pulses off of the retroreflector arrays left on the moon by the Apollo astronauts, APOLLO is capable of one-millimeter range-precision. By determining the exact shape of the lunar orbit, it will be possible to test the equivalence principle, the time-rate-of-change of the gravitational constant, gravitomagnetism, and geodetic precession to at least ten times better precision than currently tested. In addition, APOLLO will be sensitive to departures from the inverse-square law of gravity and can potentially probe the effects of extra dimensions to which only gravity has access. APOLLO's record-breaking successes thus far will be reported.
November 17, 2006 | 12:00 PM | LASR Conference Room | Friday noon seminar New Views of the High-Redshift Universe Peng Oh, University of California, Santa Barbara
Our knowledge of the high-redshift grows apace. I discuss some theoretical interpretation of recent observations of the z~6 universe in quasar absorption lines and high-redshift Lyman-alpha emitters, and implications for the reionization. I then focus on prospects for detection of the high-redshift IGM in 21cm emission, and in particular novel techniques for mining the forthcoming data.
October 2, 2006 | 12:00 PM | AAC 123 | Special Seminar Molecules in Wonderland: Nonequilibrium processes in the interstellar medium John Black, Onsala Space Observatory, Chalmers University of Technology
The chemical and physical states of an interstellar cloud are far out of thermodynamical equilibrium. The distinctions between microscopic and macroscopic phenomena defy normal human experience: an interstellar cloud is a molecular wonderland in which the collisional mean-free-path can approach the size of our solar system. The abundances and excitations of interstellar molecules are controlled by processes that have a wide range of characteristic temperatures and that are sometimes intrinsically non-thermal. This seminar will concentrate on one example of molecular ions that may probe non-equilbrium processes. The formyl ion, HCO+, is widely observed and relatively abundant in diffuse molecular gas. In this environment the chemical time-scales are short enough that the abundances of HCO+ and its highly reactive isomer HOC+ might be expected to reflect a chemical steady state. Based on well studied chemical reactions and measured abundances of the potential parent molecules of these ions, we can make an empirical analysis of the budget of formation and destruction rates in order to test the assumption of steady state (A. Tappe & J. H. Black, in preparation).
October 12, 2006 | 10:30 AM | LASR | Special Seminar Dust in Active Galactic Nuclei Martin Gaskell, University of Nebraska
The ultra-violet spectra of quasars have been widely assumed to be unreddened, yet in the optical and IR active galactic nuclei show signs of reddening. I show that the solution to this paradox is that the dust in active galactic nuclei is unlike any hitherto known. I discuss the variety of extinction curves seen in AGNs. The dust has been substantially modified by the harsh environment of the AGNs. Reddening of AGNs has wide-ranging implications both for understanding how black hole accretion works and the role of AGNs in galaxy formation. The continuum spectral energy distributions of different types of AGNs are not radically different. This supports unified pictures of accretion power from scales of stellar mass objects up to supermassive black holes. The presence of dust means that AGNs are more plentiful and more luminous than has hitherto been thought. This has implications for the formation of supermassive black holes in the nuclei of galaxies in the early universe.