Astrophysics Science Division Colloquium Series
Schedule: Summer 2013

Astrophysics Science Division Colloquium Series
Schedule: Summer 2013

Recent schedules:

  • 2013, Spring
  • 2012, Fall
  • 2012, Spring
  • 2011, Fall
  • 2011, Spring
  • 2010, Fall
  • 2010, Spring

    ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
    in Bldg 34, Room W150 unless otherwise noted.


    Jun 4 Brad Benson (Chicago) - Cluster Shadows in the Microwave Sky: Discovering the Most-Massive, Distant Clusters of Galaxies using the South Pole Telescope
    Jun 11 Johannes Staguhn (GSFC) - Deep Surveys with GISMO : Searching for submillimeter galaxies at the highest redshifts
    Jun 25 Matt Greenhouse (GSFC) - The James Webb Space Telescope: Mission Overview and Status
    Rescheduled for August 13th


    Jul 2 Katie Mack (Melbourne) - Dark Matter Particle Physics and Cosmological Evolution
    Jul 9 Robert Tyler (UMD/GSFC) - Heat generated by ocean tides on icy satellites in the Solar System (and Universe)
    Jul 16 Francesco Tombesi (GSFC) - The X-ray view of winds in Active Galactic Nuclei
    Jul 30 John Cannizzo (GSFC) - The Relativistically Beamed Tidal Disruption Event Sw J1644+57


    Aug 6 Eli Dwek (GSFC) - How Dark is the Night Sky, and Why Does it Matter?
    Aug 13 Matt Greenhouse (GSFC) - The James Webb Space Telescope: Mission Overview and Status
    Aug 20 Brian Williams (GSFC) - Examining the Nature of Type Ia Supernovae from their Remnants
    Aug 27 M. Coleman Miller (UMD) - Neutron Stars and Their Planets

    Cluster Shadows in the Microwave Sky: Discovering the Most-Massive, Distant Clusters of Galaxies using the South Pole Telescope

    Brad Benson


    Tuesday, June 4, 2013


    The cosmic microwave background (CMB) is one of our most unique, and powerful, tools to study cosmology. It gives us a snapshot of the content and structure of the Universe at a time only 400,000 years after the Big Bang, while also acting as a backlight to the entire observable Universe - a mechanism that imprints the CMB with signatures of structure formation during its 14 billion year journey. I will discuss recent measurements from the South Pole Telescope (SPT), which has imaged the CMB with an unprecedented combination of depth, area, and resolution. I will give an overview of the SPT cluster survey, a new catalog of ~400 of the most massive, distant clusters in the Universe, and the latest cosmological results from the SPT survey, including: constraints on dark energy, the sum of the neutrino masses, and the number of relativistic particle species. I will also give an overview of the SPT cluster follow-up program and efforts to improve the cluster mass calibration, including large X-ray programs on Chandra and XMM, and a weak lensing program using the Magellan and Hubble telescopes. Finally, I will give the status of plans to equip the SPT with even more sensitive polarization-sensitive instruments, including the currently operating SPTpol and the future SPT-3G experiments. SPTpol and SPT-3G will make high signal-to-noise measurements of the polarization of the CMB, and will additionally expand the SPT cluster survey by over an order of magnitude.

    Deep Surveys with GISMO : Searching for submillimeter galaxies at the highest redshifts

    Johannes Staguhn


    Tuesday, June 11, 2013


    The GISMO 2 mm camera is currently the only bolometer camera operating at the IRAM 30m telescope, and is available to the astronomical community through the semi-annual IRAM call for proposals. GISMO provides a general capability across a wide range of astronomical sources, including observations of galactic dust and free-free emission, the characterization of the SEDs of nearby galaxies, and detecting dusty galaxies at high redshifts. The 2 mm band is in particular well suited to trace the first dusty galaxies in the universe, since their redshifted SEDs peak close to GISMO's observing frequency, whereas the medium redshift galaxy foreground is almost invisible in this band. This effect makes GISMO's deep field observations a valuable complement, rather than a redundancy to the HERSCHEL far-infrared and sub-mm surveys. There are two ongoing deep sky surveys with GISMO and following a brief summary of a sample of ongoing projects, I will describe one of those surveys in detail: the GISMO Deep Field (GDF) survey, which is centered on the Hubble Deep Field North. This survey by now has reached the confusion limit and we have extracted 12 + 3 sources in a 7 arcminute wide field, of which roughly half have known submillimter galaxy counterparts, including the enigmatic submillimeter source SCUBA-850.1. A comparison of our observations with model predictions shows that our results are in good agreement with galaxy count models. Among the sources without counterparts we anticipate a significant number of sources to be at very high redshifts (z~6 and above). Follow-up observations are scheduled. Our detailed statistical analysis of the GDF data provides a solid estimate of the expected rate of false detections among those source identifications and the effect of the high density high redshift galaxies in this near confusion limited dataset on the extracted source statistics. Finally, I will give an outlook into the future by outlining the variety of science questions which we anticipate to address in the future with 2-mm deep survey data.

    Dark Matter Particle Physics and Cosmological Evolution

    Katie Mack


    Tuesday, July 2, 2013


    I will present a summary of current prospects for constraining dark matter models in high-redshift astronomy and discuss new avenues of investigation (and work in progress), including a self-consistent treatment of dark matter particle physics in cosmological simulations. Dark matter annihilation or decay in the era of galaxy formation has the potential to alter the evolution of early structures and the intergalactic medium, which may be detectable in the high-redshift 21cm signal of neutral hydrogen. I will discuss how feedback effects between different regimes of dark matter energy injection can alter the formation and evolution of the first stars and galaxies in previously unexplored ways.

    Heat generated by ocean tides on icy satellites in the Solar System (and Universe)

    Robert Tyler


    Tuesday, July 9, 2013


    Observations by the Galileo and Cassini spacecrafts have provided a strong indication that our massive water ocean is only one of at least several others in the Solar System. It is clear that these oceans would have long ago frozen if not for an internal heat source. It is also clear that in at least some of these cases (e.g. Enceladus), the heat sources previously presumed are insufficient. Recently, it has been shown by the author that if these oceans occupy one of several plausible resonant configurations, then the tidal response and heat can easily maintain liquid oceans on most of the satellites. It has also been shown that these resonant configurations are not just possible but may be inevitable because an ocean attempting to freeze will be pushed into the resonant configurations, with the increase in heat acting to stall further freezing. The results suggest that because of this stabilizing effect, liquid oceans may be common in the Universe.

    The X-ray view of winds in Active Galactic Nuclei

    Francesco Tombesi


    Tuesday, July 16, 2013


    Our X-ray view of Active Galactic Nuclei (AGN) winds has significantly improved in recent years. In this talk I will briefly review some of the main observational results in this field. For instance, supporting evidences for highly ionized, high column, ultra-fast outflows (UFOs) have been reported through the detection of blue-shifted Fe K absorption lines with velocities up to ~0.1-0.3c. Their overall characteristics suggest a direct identification with winds ejected from the inner accretion disk. High signal-to-noise soft X-ray observations of the more "classical" warm absorbers (WAs) showed that they are indeed composed of several layers of outflowing gas, suggesting that some form of ionized absorption could actually be ubiquitous in AGNs. Moreover, these winds have been observed in both radio-quiet and radio-loud AGNs, the UFOs also showing a tentative connection with prominent disk-jet ejection cycles. Significant correlations between the parameters of the WAs and UFOs have been reported, suggesting their possible unification as a single, large-scale stratified outflow observed at different locations along the line of sight, from the vicinity of the central black hole up to the outskirts of the AGN host galaxy. Their detailed acceleration mechanism(s) are still not known yet, but observations and theoretical results favor a combination of radiation pressure and/or MHD processes. The deposition of mass and energy of these winds, and especially the UFOs, in the AGN host galaxy can be substantial and, indeed, they may represent the long sought-after agent mediating the "quasar mode" feedback. Finally, important improvements in these studies are expected from the upcoming Astro-H mission.

    The Relativistically Beamed Tidal Disruption Event Sw J1644+57

    John Cannizzo


    Tuesday, July 30, 2013


    Sw J1644+57 made a dramatic appearance in March 2011, and has been the focus of intense observations spanning a wide wavelength range. It has also stimulated much theoretical work on tidal disruption events in general and jetted events in particular. Sw 1644 was unexpected; almost all previous work on TDEs, both theoretical and observational, had been centered on observational properties of the thermal emission from the accretion. In Sw 1644 our line of sight lies along the SMBH jet, so that we see only the boosted, jet emission. There now exists a ~500 d light curve of the burst from Swift/XRT. I will provide an overview of the current observational and theoretical status.

    How Dark is the Night Sky, and Why Does it Matter?

    Eli Dwek


    Tuesday, August 6, 2013


    The darkness of the night sky is an important number with important cosmological implications. In this talk I will describe the quest to determine this number, to decompose it into its foreground contributions, and to derive the intensity of the extragalactic background light (EBL). I will present the latest results in determining the EBL from direct observations, by counting the light from galaxies, and by analyzing the gamma-ray spectrum from blazars. I will also discuss models for the EBL and the resulting gamma-ray opacity of the universe.

    The James Webb Space Telescope: Mission Overview and Status

    Matt Greenhouse


    Tuesday, August 13, 2013


    Often considered to be the successor to the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST) is on schedule for launch to the Earth-Sun L2 point during 2018. The JWST is a 6.5 m class cryogenic optical/infrared observatory that will serve the international astronomical community in a manner similar to the HST. Science requirements for the mission have been derived from four themes spanning observation of the first galaxies to form after the Big Bang to the study of planetary systems (including our own Solar system). The JWST instrument payload provides imagery, spectroscopy, and coronagraphy over the 0.6--28 micron spectrum with diffraction limited angular resolution at 2 microns. This talk will present an overview of the JWST mission, its science objectives, flight system development status, and operations plans.

    Examining the Nature of Type Ia Supernovae from their Remnants

    Brian Williams


    Tuesday, August 20, 2013


    In the past decade, observations of Type Ia supernovae have revolutionized our view of the cosmos, leading to the discovery of dark energy and an accelerating universe. Yet remarkably little is known about these important explosions, and our knowledge seems to be regressing with time. Whereas it was once virtually certain that all Type Ia supernovae result from a white dwarf accreting matter from a more massive companion in a binary system until pushed beyond the point of stability, it is now doubted that this mechanism can account for most Type Ia supernovae observed, and other channels, such as colliding white dwarfs, have been proposed as more viable alternatives. I will discuss observations of the remnants of Type Ia supernovae, and what information and constraints can be extracted from these remnants in regards to their progenitor systems. I will focus on several young Type Ia supernova remnants in our Galaxy, all of which have a connection to historical astronomy. I review the physics of supernova explosions, as well as that of supernova remnants, with an emphasis on using a multi-wavelength approach to observations.

    Neutron Stars and Their Planets

    M. Coleman Miller


    Tuesday, August 27, 2013


    The pace of discovery of extrasolar planets continues to increase, yet the inner planet in the first system discovered remains the smallest-mass planet ever seen. Its detection was possible because it and its two fellow planets orbit a millisecond pulsar. Such pulsars are so remarkably stable in their rotation that asteroids could be detected around them, but in the more than two decades since only two other planets have been seen around pulsars. Moreover, in the honored tradition of astrophysics, the three systems appear to have formed via three different mechanisms. I will review these objects and discuss what they mean for planet formation, millisecond pulsar origins, and the dynamics of dense stellar systems.

    Jeremy Schnittman
  • NASA Logo, National Aeronautics and Space Administration