KICP Seminars & Colloquia, Fall 2014

Seminar schedule for Fall 2014
October 1, 2014
Wednesday colloquium
Daniel Holz
University of Chicago
Gravitational wave astrophysics with LIGO   [Abstract]
October 3, 2014
Friday noon seminar
Anja von der Linden
DARK + KIPAC
Weighing the Giants: Accurate Weak Lensing Mass Measurements for Cosmological Cluster Surveys   [Abstract]
October 7, 2014
Astronomy Special Seminar
Marcelle Soares-Santos
Fermilab
Understanding cosmic acceleration with DES and beyond   [Abstract]
October 7, 2014
Special seminar
Marcelle Soares-Santos
Fermilab
Understanding cosmic acceleration with DES and beyond   [Abstract]
October 8, 2014
Astronomy Colloquium
Jacob Bean
University of Chicago
Exoplanets in HD   [Abstract]
October 10, 2014
Friday noon seminar
Raquel H Ribeiro
Case Western Reserve University
Effective field theories for cosmic acceleration   [Abstract]
October 15, 2014
Wednesday colloquium
Daniel Chung
University of Wisconsin, Madison
Cosmological Imprints of Dark Matter Produced During Inflation   [Abstract | PDF]
October 16, 2014
Special seminar
Tejaswi Venumadhav
Caltech
The 21cm line as a new probe of magnetic fields in the pre-reionization epoch   [Abstract]
October 17, 2014
Friday noon seminar
Claude-Andre Faucher-Giguere
Northwestern University
Bridging the gap between cosmology and star formation: Feedback on galactic and cosmological scales   [Abstract]
October 22, 2014
Wednesday colloquium
Rashid Sunyaev
Max-Planck Institute for Astrophysics
Two milestones in the history of the Universe: last scattering surface and black body photosphere of the Universe   [Abstract]
October 24, 2014
Friday noon seminar
Beth A Reid
UC Berkeley
Exploiting the non-linear regime of galaxy clustering in SDSS-III BOSS   [Abstract]
October 28, 2014
Special seminar
Aaron S Chou
Fermilab
Searching for axion radio broadcasts from the galaxy   [Abstract | PDF]
October 28, 2014
Astronomy Special Seminar
Aaron Chou
Fermilab
Searching for Axion Radio Broadcasts from the Galaxy   [Abstract | PDF]
October 29, 2014
Astronomy Colloquium
Dong Lai
Cornell University
Merging Compact Binaries   [Abstract]
October 31, 2014
Friday noon seminar
Esra Bulbul
Harvard-Smithsonian Center for Astrophysics
The Curious Case of the 3.57 keV Emission Line   [Abstract]
November 5, 2014
Astronomy Colloquium
Fiona Harrison
California Institute of Technology
Science Highlights from the Nuclear Spectroscopic Telescope Array (NuSTAR): Bringing the High Energy Universe into Focus   [Abstract]
November 6, 2014
Astronomy Colloquium
Victoria Kaspi
McGill University
The Hunt for Millisecond Pulsars   [Abstract]
November 7, 2014
Friday noon seminar
Benjamin R. Safdi
MIT
Directional Detection of the Cosmic Neutrino Background   [Abstract]
November 7, 2014
Astronomy Special Seminar
Fabienne Bastien
Penn State
Enhancing Exoplanet Discovery and Characterization through Stellar Photometric "Flicker"   [Abstract]
November 11, 2014
Open Group seminar
Daan Meerburg
Johns Hopkins University
Multi wavelength constraints on the inflation   [Abstract]
November 12, 2014
Wednesday colloquium
Peter F Michelson
Department of Physics, Stanford University
The Fermi Gamma-Ray Space Telescope: An Update   [Abstract | PDF]
November 14, 2014
Friday noon seminar
Anna Franckowiak
SLAC / KIPAC
The Fermi bubbles   [Abstract]
November 18, 2014
Astronomy Special Seminar
Irina Zhuravleva
Stanford University
Turbulent heating in the cores of galaxy clusters and its role in AGN-feedback   [Abstract]
November 19, 2014
Astronomy Colloquium
Andrei Beloborodov
Columbia University
Luminous neutron stars   [Abstract]
November 21, 2014
Astronomy Special Seminar
Andrei Beloborodov
Columbia University
Emission mechanism of gamma-ray bursts   [Abstract]
November 21, 2014
Friday noon seminar
Liang Dai
Johns Hopkins University
Conformal Fermi coordinates and the local universe formalism   [Abstract]
December 3, 2014
Astronomy Colloquium
Matthew Kunz
Princeton University
From Plasma Microphysics to Global Dynamics in Clusters of Galaxies, Hot Accretion Flows, and the Solar Wind   [Abstract]
December 9, 2014
Astronomy Special Seminar
Blakesley Burkhart
Harvard University
New Frontiers of Magnetized Turbulence in the Multiphase Interstellar Medium   [Abstract]
December 10, 2014
Wednesday colloquium
Daniel Akerib
SLAC
Do WIMPs Rule? The LUX & LZ Experiments and the Search for Cosmic Dark Matter   [Abstract | PDF]
December 12, 2014
Friday noon seminar
Brendan Crill
Jet Propulsion Laboratory
Results from Planck 2014   [Abstract]
 
WEDNESDAY COLLOQUIA

  • October 1, 2014 | 3:00 PM | BSLC 115
    Gravitational wave astrophysics with LIGO
    Daniel Holz, University of Chicago

    Gravitational waves were first predicted by Einstein almost a century ago, and the Laser Interferometer Gravitational wave Observatory (LIGO) should be finally on the verge of directly detecting these waves. The most likely sources are the inspirals and mergers of stellar mass binary systems, such as pairs of neutron stars and/or black holes. In addition to being extraordinarily loud in gravitational waves, these coalescences may be associated with short gamma-ray bursts, and thus hold out the promise of multi-messenger astronomy: combining gravitational wave and electromagnetic observations to elucidate the physics and astrophysics of the sources. We present estimates for the event rate of binary systems, showing that LIGO can expect the first detections within months of operation. We examine the sky localization of LIGO sources, and explore some of the results that can be expected from gravitational wave astronomy, including shedding light on the process of black hole formation and precision measurements of the Hubble constant. We also discuss the loudest gravitational wave sources, and the potential to use these for internal calibration as well as for science. The era of gravitational-wave astronomy is rapidly approaching; a revolutionary new probe of our Universe awaits.
  • October 15, 2014 | 3:00 PM | BSLC 001
    Cosmological Imprints of Dark Matter Produced During Inflation
    Daniel Chung, University of Wisconsin, Madison

    PDF
    Dark matter produced during inflation can naturally leave observable isocurvature imprints in the inhomogeneities of our universe. I survey the progress in theoretically cataloging such imprints, along with their connections with high energy theory and observations.
  • October 22, 2014 | 3:00 PM | BSLC 109
    Two milestones in the history of the Universe: last scattering surface and black body photosphere of the Universe
    Rashid Sunyaev, Max-Planck Institute for Astrophysics

    Reception at 4 PM in the LASR conference room.
  • November 12, 2014 | 3:00 PM | BSLC 001
    The Fermi Gamma-Ray Space Telescope: An Update
    Peter F Michelson, Department of Physics, Stanford University

    PDF
    The Fermi Gamma-Ray Space Telescope was launched in 2008. After 6 years in orbit, Fermi continues to bring new insights into the sources of high-energy radiation in the Galaxy and beyond. In this talk, I will describe upgrades to the science performance of Fermi (aka Pass 8) and highlights of recent discoveries.
  • December 10, 2014 | 3:00 PM | BSLC 001
    Do WIMPs Rule? The LUX & LZ Experiments and the Search for Cosmic Dark Matter
    Daniel Akerib, SLAC

    PDF
    Dark Matter remains a profound mystery at the intersection of particle physics, astrophysics, and cosmology. One of the leading candidates, the Weakly Interacting Massive Particle, or WIMP, may be detectable using terrestrial particle detectors. Recent technological advances are enabling very rapid increases in sensitivity in the search for these particles. I will talk about the LUX experiment, a liquid xenon time projection chamber, which currently holds the best upper limit over much of the mass range. I will also discuss plans for a larger follow up experiment, LZ, which will just begin to measure a background neutrino signal that will set a fundamental limit our ability to search for WIMP dark matter.

 
FRIDAY NOON SEMINARS

  • October 3, 2014 | 12:00 PM | LASR conference room
    Weighing the Giants: Accurate Weak Lensing Mass Measurements for Cosmological Cluster Surveys
    Anja von der Linden, DARK + KIPAC

    Surveys of galaxy clusters provide a sensitive probe of cosmology by measuring the evolution of the halo mass function. With a number of surveys at optical, millimeter, and X-ray wavelengths on-going or starting in the near futures, cluster count experiments will be one the most important cosmological probes over the next decade. However, none of the typical survey observables (X-ray luminosity, optical richness, SZ flux) directly measures the cluster mass. Already current cluster surveys are systematically limited by uncertainties in the relation between cluster mass and observables. Cluster weak lensing is the most promising observational method to calibrate the mass scaling to the required precision, but requires the control of systematic errors to a few percent each. I will review our "Weighing the Giants" project to measure accurate individual weak lensing masses for the largest sample of clusters to date, and discuss its first cosmological applications for cluster count experiments as well as the baryonic mass fraction test.
  • October 10, 2014 | 12:00 PM | LASR Conference Room
    Effective field theories for cosmic acceleration
    Raquel H Ribeiro, Case Western Reserve University

    In this era of precision cosmology we are relying more than ever on our theories to decode observations. Models phrased in an Effective Field Theory (EFT) language are particularly useful, since they rely on the existence of a decoupling limit which makes the low energy physics phenomena largely independent of short distance physics. Why is such description desirable? It means we don't need to know the full behaviour of the theory, but only its low energy limit to make predictions for observables at the scale of the experiment we are interested in. In this talk I will discuss a different reorganisation of EFTs describing single-field models for cosmic acceleration (in the early and late universe) with large derivative interactions. The decoupling limit in these theories relies on a derivative hierarchy, rather than a hierarchy between energy scales. Examples include Dirac--Born--Infeld inflation and galileon models in the context of modified gravity. I will discuss the criterion of predictivity of these theories and identify the scales up to which the predictions of these theories are reliable to decode observational data.
  • October 17, 2014 | 12:00 PM | LASR Conference Room
    Bridging the gap between cosmology and star formation: Feedback on galactic and cosmological scales
    Claude-Andre Faucher-Giguere, Northwestern University

    Star formation is observed to be very inefficient, both within galaxies and cosmologically. Feedback from massive stars and growing black holes has emerged as the most promising solution to explain these facts and broadly bring galaxy formation models in agreement with observations. However, most galaxy formation models to date have had to rely on significant simplifying assumptions and parameters must typically be tuned to obtain realistic galaxy populations. I will argue that the predictive power of cosmological simulations of galaxy formation can now be greatly improved by directly resolving the main structures in the interstellar medium of galaxies and bridging the historical gap between cosmological models and detailed studies of star formation and feedback on galactic scales. I will present new high-resolution simulations of supernova remnant evolution in an inhomogeneous medium and show how the results can be used to model supernova feedback more accurately in cosmological simulations. I will then introduce the FIRE ("Feedback In Realistic Environments") cosmological simulation project and present early results on the predicted stellar mass function of galaxies, galactic winds, and properties of halo gas around high-redshift galaxies.
  • October 24, 2014 | 12:00 PM | LASR Conference Room
    Exploiting the non-linear regime of galaxy clustering in SDSS-III BOSS
    Beth A Reid, UC Berkeley

    The size of both galaxy redshift surveys and N-body simulations of dark matter clustering have grown tremendously over the past few decades, which provides the opportunity to exploit the quasi- and non-linear regime for cosmological information. I will discuss the observational and theoretical challenges in measuring and modeling the small-scale redshift space clustering of galaxies in SDSS-III BOSS, as well as its great promise -- we infer the growth rate of cosmic structure at z=0.57 to 2.5% precision and robustly predict the impact of "galaxy" physics on clustering in the quasi-linear regime. I will demonstrate quantitatively the importance of precise models for broadband clustering in the quasi-linear regime for future redshift survey constraints on dark energy and neutrino mass.
  • October 31, 2014 | 12:00 PM | LASR Conference Room
    The Curious Case of the 3.57 keV Emission Line
    Esra Bulbul, Harvard-Smithsonian Center for Astrophysics

    We recently detected an unidentified emission line at 3.57 keV in the Chandra observations of the Perseus cluster and the stacked XMM-Newton observations of 73 galaxy clusters. This line was detected at >3sigma statistical significance in five independent samples of XMM-Newton. The lack of any atomic transitions at this energy in thermal plasma, hints that the line could be a signature of decaying sterile neutrinos. I will discuss the search for this line in the stacked observations of galaxy clusters and provide an update on active searches for this feature in other dark matter rich astrophysical systems.
  • November 7, 2014 | 12:00 PM | LASR Conference Room
    Directional Detection of the Cosmic Neutrino Background
    Benjamin R. Safdi, MIT

    The cosmic neutrino background (CvB), produced about one second after the Big Bang, permeates the Universe today. New technological advancements make neutrino capture on tritium a promising path forward towards the detection of the CvB. I will show that gravitational focusing by the Sun causes the expected neutrino capture rate to modulate annually. The amplitude and phase of the modulation depend on the phase-space distribution of the local neutrino background, which is perturbed by structure formation. Gravitational focusing is the only source of modulation for neutrino capture experiments, in contrast to dark-matter direct-detection searches where the Earth's time-dependent velocity relative to the Sun also plays a role. I will also show that CvB observatories may measure anisotropies in the cosmic neutrino velocity and spin distributions by polarizing the tritium targets. The polarized-target measurements may constrain non-standard neutrino interactions, such as neutrino magnetic dipole moment interactions, that would induce larger anisotropies and help discriminate between Majorana versus Dirac neutrinos.
  • November 14, 2014 | 12:00 PM | LASR Conference Room
    The Fermi bubbles
    Anna Franckowiak, SLAC / KIPAC

    The Fermi bubbles are two large structures in the gamma-ray sky extending up to 55 deg above and below the Galactic center. I will present the analysis of 50 months of Fermi-LAT data from 100 MeV to 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. I will show results on the spectral shape, spatial substructure, variability of the spectrum as a function of latitude and an estimate of the width of the bubble boundary. I will discuss the modeling of the gamma-ray spectrum with hadronic and leptonic models and the possible relation to the microwave haze.
  • November 21, 2014 | 12:00 PM | LASR Conference Room
    Conformal Fermi coordinates and the local universe formalism
    Liang Dai, Johns Hopkins University

    In an inhomogeneous Universe, the physical effect of long-wavelength perturbation on short distances should be such that short-wavelength perturbations effectively evolve in a modified homogeneous universe. We explicitly construct the so-called conformal Fermi normal coordinates (CFNC) through an expansion around the observer's geodesic, which describe the local spacetime as a quasi-FRW metric and are valid at all times. The CFNC formalism demonstrates that the zeroth-order picture is that local expansion rate and spatial curvature are renormalized by long-wavelength perturbations, and the general condition for the spatial curvature to be a constant is derived. Beyond this "separate universe" picture, CFNC allows for systematic survey of additional local effects from long-wavelength perturbations that cannot be attributed to a re-definition of the background FRW cosmology. The formalism can be useful in the studies of tracer bias, intrinsic alignment and gravitational-wave "fossil" effect.
  • December 12, 2014 | 12:00 PM | LASR Conference Room
    Results from Planck 2014
    Brendan Crill, Jet Propulsion Laboratory

    Planck is the third-generation space mission aimed at measuring the Cosmic Microwave Background, a relic of the hot big bang. Launched in May 2009 Planck has surveyed the full sky in intensity and polarization with a broad range of frequencies from 30 to 857 Ghz at a resolution as fine as 5 arcminutes above 143Ghz. This month, the Planck collaboration is releasing science results and data from polarization maps of the sky from 30 to 353 GHz. In this talk, I will present the new polarized sky maps from Planck and give an overview of their impact on our understanding of the standard Lambda-CDM cosmological model. I will also discuss what Planck's data can tell us about Galactic polarized foreground emission that potentially impacts current and future searches for the imprint of inflationary gravitational waves on B-mode polarization.

 
SPECIAL SEMINARS

  • October 7, 2014 | 12:00 PM | LASR Conference Room
    Understanding cosmic acceleration with DES and beyond
    Marcelle Soares-Santos, Fermilab

    The Dark Energy Survey (DES) is a large imaging sky survey designed to enable us to understand the physics underlying the accelerated expansion of the recent Universe. This cosmic acceleration can be explained either by invoking a new energy component to the Universe, dark energy, or by introducing a new fundamental theory of gravity. In either case it is one of the greatest scientific challenges of our time. DES data is used to measure the cosmic expansion rate history and the growth of large-scale structure using complementary techniques such as: type Ia Supernovae, galaxy cluster counts and weak gravitational lensing. In this talk, I present our recent results, describe an initiative to develop a new future technique - cosmic sirens - and discuss the prospects for improving our understanding of cosmic acceleration with DES data. I will also discuss, briefly, the long term evolution of this research program beyond DES, with the Large Synoptic Survey Telescope (LSST) and the Giant Magellan Telescope (GMT). LSST is a future imaging survey that will cover larger area and will achieve higher depth than DES. GMT is a next generation 30-meter class telescope with superb imaging and spectroscopic capabilities.
  • October 16, 2014 | 1:00 PM | LASR Conference Room
    The 21cm line as a new probe of magnetic fields in the pre-reionization epoch
    Tejaswi Venumadhav, Caltech

    Mapping neutral hydrogen using the 21cm line is commonly considered to be the next big observational frontier in cosmology. Its main advantage is that it provides redshift information, and enables access to many more modes than the CMB does. I will highlight another feature of the line which makes it possible to extract even more interesting cosmological information from high resolution 21cm observations, when they are realized in the future. This is the spin-degeneracy of the triplet excited state of the transition, which is spin-polarized by anisotropies in the incident radiation. In this talk, I will focus on fluctuations in the brightness temperature seen by a present-day observer, and show that they encode information about magnetic fields which are coherent on large scales in the early universe. This technique will be naturally sensitive to extremely weak field strengths of order 10^{-19} G, which opens the possibility of probing primordial magnetic fields in neutral gas prior to reionization. I will also briefly touch upon the exciting, if even more speculative possibility of studying tensor modes using the 21cm line.
  • October 28, 2014 | |
    Searching for axion radio broadcasts from the galaxy
    Aaron S Chou, Fermilab

    PDF
    Originally proposed to solve the mystery of the vanishing neutron electric dipole moment, axions have emerged as one of the leading candidates to explain the dark matter of the universe. In this seminar, I will explain the principles of the resonant microwave cavity technique used by the ADMX experiment to directly detect the local flux of dark matter axions, and the challenges that will be faced as the search for the dark matter broadcast frequency progresses from the 1 GHz band up to 10 GHz and beyond. I will also briefly cover ideas to utilize instrumentation from the CMB/FIR communities to enable future probes: superconducting bolometers for higher frequencies 10-300 GHz, and frequency multiplexed readouts for lower frequencies <1 GHz.

 
OPEN GROUP SEMINARS

  • November 11, 2014 | 11:00 AM | LASR Conference Room
    Multi wavelength constraints on the inflation
    Daan Meerburg, Johns Hopkins University

    The detection of tensor modes in CMB polarization by the Background Imaging of Cosmic Extragalactic Polarization, and their possible primordial origin as relic gravitational waves has invigorated the cosmological community. There has been much debate about possible systematics in the BICEP2 data, and this is an important observational concern that will be resolved with independent measurements and multi-frequency observations. However, the observations themselves have yielded much renewed interest in constraining models of inflation through their predictions for the level of gravitational waves generated during inflation, and the ‘testability’ of the inflationary scenario. One possible way to test the inflationary scenario is to verify or falsify the inflation consistency condition, which relates the amplitude of gravitational wave amplitude to its scale dependence; if tensors and scalars are sourced by the same mechanism, more power on small scales would violate the null energy condition and would suggest inflation is not responsible for the tensor modes. Much discussion has been aimed at how well we could do with future observations; here I will present some results we derived from combining current data. I will show that constraints from LIGO and PTA already constrain the posterior parameter volume significantly. In addition I will show that in order to consistently use the CMB data to constrain the inflation consistency condition we should include effects of the gravitational background density on the expansion history of the Universe.

 
ASTRONOMY COLLOQUIA

  • October 8, 2014 | 3:00 PM | BSLC 001
    Exoplanets in HD
    Jacob Bean, University of Chicago

    Exoplanet surveys have revealed an amazing diversity of planets orbiting other stars in the last two decades. Studying the atmospheres of representative exoplanets is the key next step in leveraging these detections to further transform our understanding of planet formation and planetary physics. Additionally, atmospheric studies are critical for determining if any of the small habitable zone exoplanets that are now being detected are truly habitable, and even inhabited. In this talk I will describe a vision for how we can pursue the compelling opportunities in exoplanet atmospheres today and in the future. One crucial need in this area is spectroscopy to reveal planets in high definition. I will present new results from intensive observational campaigns with the Hubble Space Telescope that serve as a model for the proposed program, including a definitive constraint on the atmosphere of the super-Earth archetype GJ1214b, a precise measurement of the water abundance in a giant planet, and the inference of the thermal structure of an exoplanet atmosphere as a function of longitude. A fundamental component of the envisioned approach for the future is the need for a strategic program combining observations with multiple ground- and space-based telescopes using a suite of techniques to investigate the question of habitability. I will conclude by discussing how future facilities like the Giant Magellan Telescope are poised to play a crucial role in the identification of the first Earth twin as part of this plan.
  • October 29, 2014 | 3:00 PM | BSLC 001
    Merging Compact Binaries
    Dong Lai, Cornell University

    The merger of binary systems containing neutron stars, black holes or white dwarfs can lead to various extreme phenomena that are observable throughout the universe. I will discuss recent works on merging neutron star/black hole binaries and white dwarf binaries, focusing on dynamical processes in the pre-merger phase, gravitational waves, tidal and electromagnetic interactions, and potential constraint on dense nuclear matter.
  • November 5, 2014 | 3:00 PM | BSLC 001
    Science Highlights from the Nuclear Spectroscopic Telescope Array (NuSTAR): Bringing the High Energy Universe into Focus
    Fiona Harrison, California Institute of Technology

    The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray (3 - 79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate. With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants. I will describe the mission and present recent science highlights.
  • November 6, 2014 | 4:00 PM | KPTC 106
    The Hunt for Millisecond Pulsars
    Victoria Kaspi, McGill University

    The continued search for more of nature's most perfect clocks -- millisecond radio pulsars -- has recently taken a more urgent turn given the potential of these objects to detect and study gravitational waves from a variety of potential sources, most likely merging supermassive black holes. Additionally, their discovery has invariably led to surprising and interesting astrophysical results as novel binary MSPs are revealed and studied. Such bonuses include constraints on the equation-of-state of dense matter, tests of theories of gravity, as well as surprises in binary evolution. Most recently, the hunt for millisecond pulsars has led to a new, serendipitous discovery, the so-called 'Fast Radio Bursts,' few-ms single pulses of unknown origin, from apparently cosmological distances. Here I describe ongoing millisecond pulsar searches and their recent bounty, as well as plans for future study of these objects, as well as of single-burst sources.
  • November 19, 2014 | 3:00 PM | BSLC 001
    Luminous neutron stars
    Andrei Beloborodov, Columbia University

    Neutron stars were discovered as radio pulsars in 1967. At a glance, pulsars are merely fast-rotating magnetized spheres. They are observed to generate powerful beams of coherent radio waves and huge luminosity in gamma-rays; their emission mechanism has remained a puzzle for four decades. Today, this puzzle can be fully resolved using first-principle numerical experiments. I will describe such an experiment and its first results.Then I will discuss the most fascinating class of neutron stars -- magnetars, whose activity is fed by the dissipation of magnetic energy. I will describe the mechanism of X-ray emission from magnetars, their giant gamma-ray flares, and the behavior of the solid crust broken by magnetic stresses. Finally, I will describe the NuSTAR discovery of a new class of ultra-luminous accreting neutron stars and discuss the implications of this discovery.
  • December 3, 2014 | 3:00 PM | BSLC 001
    From Plasma Microphysics to Global Dynamics in Clusters of Galaxies, Hot Accretion Flows, and the Solar Wind
    Matthew Kunz, Princeton University

    Many astrophysical systems are magnetized and weakly collisional. As such, their mean, global properties are vastly separated in both space and time from the detailed kinetic microphysics that governs the transport of momentum, heat, and magnetic fields. Elucidating this physics is a vital step towards understanding why the intracluster medium avoids catastrophic cooling, how angular momentum is transported in hot accretion flows, and what shapes the observed distribution function in the solar wind. In this talk, I will present a unified description of these systems in terms of the pressure anisotropy, a directional bias in thermal pressure caused by adiabatic evolution in a magnetized plasma. Its impact on both micro- and macro-scales is examined using analytical theory and numerical simulations, the latter made possible by a new hybrid-kinetic particle-in-cell code, Pegasus (Kunz et al. 2014, JCoP, 259, 154). Pioneering studies of kinetic solar-wind turbulence, collisionless magnetorotational instability, and of fast-growing Larmor-scale instabilities will be placed within the larger context of formulating a pragmatic framework for modeling astrophysical multiscale plasma dynamics.

 
ASTRONOMY SPECIAL SEMINARS

  • October 7, 2014 | 12:00 PM | LASR Conference Room
    Understanding cosmic acceleration with DES and beyond
    Marcelle Soares-Santos, Fermilab

    The Dark Energy Survey (DES) is a large imaging sky survey designed to enable us to understand the physics underlying the accelerated expansion of the recent Universe. This cosmic acceleration can be explained either by invoking a new energy component to the Universe, dark energy, or by introducing a new fundamental theory of gravity. In either case it is one of the greatest scientific challenges of our time. DES data is used to measure the cosmic expansion rate history and the growth of large-scale structure using complementary techniques such as: type Ia Supernovae, galaxy cluster counts and weak gravitational lensing. In this talk, I present our recent results, describe an initiative to develop a new future technique — cosmic sirens — and discuss the prospects for improving our understanding of cosmic acceleration with DES data. I will also discuss, briefly, the long term evolution of this research program beyond DES, with the Large Synoptic Survey Telescope (LSST) and the Giant Magellan Telescope (GMT). LSST is a future imaging survey that will cover larger area and will achieve higher depth than DES. GMT is a next generation 30-meter class telescope with superb imaging and spectroscopic capabilities.
  • October 28, 2014 | 12:00 PM | LASR Conference Room
    Searching for Axion Radio Broadcasts from the Galaxy
    Aaron Chou, Fermilab

    PDF
    Originally proposed to solve the mystery of the vanishing neutron electric dipole moment, axions have emerged as one of the leading candidates to explain the dark matter of the universe. In this seminar, I will explain the principles of the resonant microwave cavity technique used by the ADMX experiment to directly detect the local flux of dark matter axions, and the challenges that will be faced as the search for the dark matter broadcast frequency progresses from the 1 GHz band up to 10 GHz and beyond. I will also briefly cover ideas to utilize instrumentation from the CMB/FIR communities to enable future probes: superconducting bolometers for higher frequencies 10-300 GHz, and frequency multiplexed readouts for lower frequencies <1 GHz.
  • November 7, 2014 | 1:30 PM | LASR conference room
    Enhancing Exoplanet Discovery and Characterization through Stellar Photometric "Flicker"
    Fabienne Bastien, Penn State

    As a result of the high precision and cadence of surveys like MOST, CoRoT, and Kepler, we may now directly observe the very low-level light variations arising from stellar granulation in cool stars. In this talk, we discuss how this enables us to more accurately determine the physical properties of Sun-like stars, to understand the nature of surface convection and its connection to activity, and to better determine the properties of planets around cool stars. Indeed, such sensitive photometric "flicker" variations are now within reach for thousands of stars, and we estimate that upcoming missions like TESS will enable such measurements for ~100 000 stars. We present recent results that tie "flicker" to granulation and enable a simple measurement of stellar surface gravity with a precision of 0.1 dex. We use this, together and solely with two other simple ways of characterizing the stellar photometric variations in a high quality light curve, to construct an evolutionary diagram for Sun-like stars from the Main Sequence on towards the red giant branch. We discuss further work that correlates "flicker" with stellar density, allowing the application of astrodensity profiling techniques used in exoplanet characterization to many more stars. We also present results suggesting that the granulation of F stars must be magnetically suppressed in order to fit observations. Finally, we show that we may quantitatively predict a star's RV jitter using our evolutionary diagram, permitting the use of discovery light curves to help prioritize follow-up observations of transiting exoplanets.
  • November 18, 2014 | 12:00 PM | LASR
    Turbulent heating in the cores of galaxy clusters and its role in AGN-feedback
    Irina Zhuravleva, Stanford University

    Radiative energy losses of the hot gas in galaxy clusters occur on timescales significantly shorter than the Hubble time, leading to massive accumulation of cold gas and vigorous star formation, in contradiction to observations. Several sources of heat have been discussed, most promising being heating by the SMBH in central galaxies through inflation of bubbles of relativistic plasma. The missing link in this scenario is the mechanisms, by which energy from bubbles is transported to the hot gas. Dissipation of gas turbulence, induced by bubbles during their buoyant rise and expansion, is a possible mechanisms. However, direct measurements of gas velocities will be possible only with future X-ray calorimeters on board the Astro-H observatory. We recently overcame this problem, by analyzing long Chandra observations of the X-ray brightest clusters of galaxies and measuring statistical properties of density fluctuations, which allowed us to constrain the velocity power spectrum of gas motions in the ICM indirectly. I will show that the heating rate due to dissipation of turbulence is indeed sufficient to balance the radiative cooling locally at each radius within the cores. Turbulent dissipation, therefore, might be the key element in resolving the gas cooling problem in cluster cores and other X-ray gas-rich systems.
  • November 21, 2014 | 1:30 AM | LASR East
    Emission mechanism of gamma-ray bursts
    Andrei Beloborodov, Columbia University

    Gamma-ray bursts (GRBs) are emitted by powerful relativistic jets from short-lived compact engines. A long-debated question is how the jet radiates the observed gamma-rays. The GRB spectra suggest that most of the radiation is produced at the opaque stage of the explosion and then released at its photosphere. In many respects, the explosion resembles the Big Bang; in this analogy, the emitted burst corresponds to cosmic microwave background. Its spectrum is shaped by radiative transfer in the expanding jet; it becomes nonthermal because of strong internal dissipation. I will describe the main stages of the explosion, the dissipation mechanism, and the radiative processes that produce the gamma-rays. Detailed transfer simulations confirm the photospheric picture and allow one to estimate the main parameters of the GRB jet -- its Lorentz factor and magnetization. I will also discuss the puzzle of long GeV flashes accompanying GRBs.
  • December 9, 2014 | 12:00 PM | LASR
    New Frontiers of Magnetized Turbulence in the Multiphase Interstellar Medium
    Blakesley Burkhart, Harvard University

    The current paradigm of the ISM is that it is a multiphase turbulent environment, with turbulence affecting many important processes. For the ISM this includes star formation, cosmic ray acceleration, and the evolution of structure in the diffuse ISM. This makes it important to study interstellar turbulence using the strengths of numerical studies combined with observational studies. I shall discuss progress that has been made in the development of new techniques for comparing observational data with numerical MHD simulations in the star forming molecular medium, in neutral gas as traced by 21 cm emission, and warm ionized gas as traced by synchrotron polarization.