Astrophysics Science Division Colloquium Series
Schedule: Fall 2015
Astrophysics Science Division Colloquium Series
Schedule: Fall 2015
Recent schedules:
| 2015, Spring | ||
| 2014, Fall | 2014, Spring | |
| 2013, Fall | 2013, Spring | 2013, Summer |
| 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.
CANDELS: Observing Galaxy AssemblyHenry FergusonSTScITuesday, Sep 15, 2015AbstractThe Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) is a multi-cycle observing program with the Hubble space telescope (and many other facilities) designed to document the first third of galactic evolution, from redshift z~8 to 1.5. It is also designed to find and measure Type Ia SNe beyond z > 1.5 and test their accuracy as standard candles for cosmology. The Hubble observations were completed in August 2013. The talk will discuss findings from ongoing analysis of the survey data , including observations of AGN hosts at high redshifts, and the evolution of structure of passive and star-forming galaxies. |
Propagation of Thermonuclear Flames on the Surface of Accreting Neutron StarsYuri CavecchiUniv. AmsterdamTuesday, Sep 22, 2015AbstractThe Type I Bursts, thermonuclear explosions on the surface layers of accreting neutron stars, produce extremely bright X-ray flashes that outshine all the other emission for tens of seconds. Their light curves encode information about star parameters such as spin, mass and radius that are key to constraining the long sought for equation of state of the matter in the interior of the neutron stars. However, to be able to fully disentangle that information from the observations, we need a solid understanding of how the burning flame propagates across the surface. The mathematical complexity of the problem makes non-approximate analytical solutions impossible and we have to rely on numerical simulations. I will present the results of ab initio calculations of the flame spreading, describing the physical mechanisms behind the propagation and their dependence on the star parameters. |
Detecting Cosmic Neutrinos with IceCube at the Earth's South PoleNaoko NeilsonDrexel UniversityTuesday, Sep 29, 2015AbstractThe IceCube Neutrino Observatory has recently discovered a diffuse flux of astrophysical neutrinos, in other words, neutrinos from beyond the solar system. But how does one collect neutrinos at the South Pole? Why study neutrinos for astronomy? In this talk, I will try to answer such questions. I will discuss the multiple diffuse flux analyses in IceCube that observe the astrophysical flux, and what each can tell us. Spatial analyses that aim to identify the sources of such astrophysical neutrinos will also be discussed, followed by an attempt to reconcile all results, to draw a coherent picture that is the state of neutrino astronomy. |
AdEPT, the Advanced Energetic Pair Telescope for Medium-Energy Gamma-Ray PolarimetryStanley D. HunterGSFCTuesday, Oct 6, 2015AbstractThe Advanced Energetic Pair Telescope (AdEPT) is being developed as a future NASA/GSFC end-to-end MIDEX mission to perform high-sensitivity medium-energy (5--200 MeV) astronomy and revolutionary gamma-ray polarization measurements. The enabling technology for AdEPT is the GSFC Three-Dimensional Track Imager (3-DTI), a large volume gaseous time projection chamber with 2-dimentional micro-well detector (MWD) readout. The low density and high spatial resolution of the 3-DTI allows AdEPT to achieve high angular resolution (~0.5 deg at 67.5 MeV) and, for the first time, exceptional gamma-ray polarization sensitivity. These capabilities enable a wide range of scientific discovery potential for AdEPT. We will discuss several of the key science goals that AdEPT will address. These include: 1) Explore fundamental processes of particle acceleration in active astrophysical objects, 2) Reveal the magnetic field configuration of the most energetic accelerators in the Universe, 3) Explore the origins and acceleration of cosmic rays and the Galactic MeV diffuse emission, 4) Search for dark matter in the Galactic center, and 5) Test relativity with polarization measurements. |
Gamma-rays from Type Ia Supernova SN2014JEugene ChurazovMPA, GermanyFriday, Oct 9, 2015AbstractSN2014J is the closest type Ia supernova in the era of space observatories and the first one from which gamma-ray lines have been detected with high significance. The flux of Co-56 lines at 847 and 1238 keV, observed with INTEGRAL, shows that about 0.6 Msun of radioactive Ni-56 has been synthesized during explosion. The line broadening suggests the characteristic expansion velocity of ~10000 km/s. Annihilation of positrons produced during decay of Co-56 makes significant contribution to the continuum below 511 keV. The total mass of the ejecta is consistent with 1.4 Msun progenitor, although the constraints are not very tight. Overall the gamma-ray data are broadly consistent with the expectations for canonical 1D models, such as delayed detonation or deflagration models for a near-Chandrasekhar mass White Dwarf. Pure detonation models or strongly sub-Chandrasekhar models are excluded by the gamma-ray data. |
The First Massive Black HolesMarta VolonteriInst. Astrophysique Paris, FranceThursday, Oct 15, 2015AbstractMassive black holes are the engines that power quasars and Active Galactic Nuclei (AGN) throughout cosmic time, and they dwell at the centers of nearby galaxies, including our own Milky Way. The discovery of quasars at z~6-7 demonstrates that massive black holes must form extremely early on and grow rapidly in order to grow to over a billion solar masses within less than 1 Gyr. In contrast to such monsters, today's black hole population extends down to small masses, and there are even galaxies bereft of central massive black holes. Therefore, studying black hole formation is needed to understand both the advent of the first luminous quasars, and the properties of black holes in today's galaxies, notably why some galaxies host a MBH, and some others do not, and what the minimum mass of a black hole is. I will critically discuss theoretical models of black hole formation in the first galaxies, the evolution of the black hole population, and possible observational diagnostics to probe how the first black holes formed. |
Pulsar Timing and Gravitational Wave AstronomySam FinnPSUTuesday, Oct 20, 2015AbstractBeyond the detection of gravitational is its potential as a tool of astronomical discovery. It is in the nature of gravitational wave emission mechanisms that the wave frequency is directly proportional to the mass of the systems that are responsible for the waves that can be observed. Thus, 100 Hz gravitational waves are associated with stellar mass binary systems, 100 mHz waves with intermediate mass black hole systems, and 0.1 mHz waves with binary black hole systems of million solar mass scale. To observe the gravitational waves from binary systems of supermassive black holes, such as arise following galactic major mergers, requires the ability to observe the presence of waves with frequencies less than or of order 100 nHz, i.e., periods of a year or more. With such observations, however, comes the prospect of tracking the evolution of their co-evolving galactic hosts and probing the environment of merged galaxies at the sub-parsec scale. In this colloquium we will explore how pulsar timing can be used to detect gravitational waves at these very low frequencies, the variety of sources that we might expect to observe, what gravitational wave observations can tell us about about conditions in the cores of merged galaxies, and the prospects for making this exciting story of discovery a reality. |
The Diverse Implications of Stellar Feedback for Galaxy FormationPhilip HopkinsCaltechTuesday, Oct 27, 2015AbstractThe most fundamental unsolved problems in galaxy formation revolve around "feedback" from massive stars and black holes. I'll present new simulations which combine new numerical methods and physics in an attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, stellar winds, and photo-ionization. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law and the global inefficiency of star formation -- the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, and many observed properties of the ISM, star formation, and galaxies can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. But feedback also produces galactic super-winds that can dramatically alter the cosmological evolution of galaxies, change the nature of dark matter cores and ‘cusps’, and re-structure the circum-galactic and inter-galactic medium. These winds depend non-linearly on multiple feedback mechanisms in a way that explains why they have been so difficult to model in previous "sub-grid" approaches. This resolves long-standing problems in understanding even apparently "simple" galaxy properties like the mass-metallicity relation. Finally, I'll discuss where stellar feedback fails, and additional feedback, perhaps from AGN, is really needed to explain observations. |
Probing the Evolution of Galaxy clusters from z~2 to z~0 with the South Pole TelescopeMike McDonaldMITTuesday, Nov 3, 2015AbstractThe South Pole Telescope (SPT), a 10m mm-wave telescope in Antarctica, has recently completed two surveys which have allowed a rapid acceleration in our understanding of how galaxy clusters form and evolve. Utilizing the Sunyaev Zel'dovich effect, data from this telescope provide a mass-selected sample of galaxy clusters at all redshifts, with the most recent survey discovering clusters out to z~2. In this talk, I will present multi-wavelength follow-up of these clusters, which allow us to probe the evolution of the hot, intracluster gas, the evolution of the central most-massive galaxy, and the evolution of the radio-loud AGN which act as thermostats in the cores of nearby clusters. These results are the first of many from this data-rich survey, and I will finish with a look forward at ongoing and planned surveys by our and other groups over the next decade. |
The next generation of astronomical instrumentation for the mm-wave and far infrared: large-scale cameras and on-chip spectrometersJochem BaselmansSRON, the NetherlandsTuesday, Nov 10, 2015AbstractObservations at infrared, submillimeter, and millimeter wavelengths will be essential for addressing many of the key questions in astrophysics. Future ground- and space based observatories need large detector arrays, with more than 104 pixels, which are limited only by the noise of the radiation background. Only superconducting detectors, operating at extremely low temperatures of 0.1K, achieve this sensitivity. Several technologies exist, such as bolometers, photoconductors and transition edge sensors, but these technologies present significant fabrication difficulties, and lead to a high degree of complexity of system integration and readout electronics for large format arrays. The Microwave Kinetic Inductance Detector, or MKID, is a relatively new and potentially game-changing superconducting detector technology, which provides background limited sensitivity over the entire FIR/mm-wavelength range and can be adapted for a variety of science goals enabling completely novel instrument concepts. Crucially, they naturally allow to read out in excess of 1000 detectors using a single readout line with very limited cryogenic hardware. On top of this MKIDs can be integrated with planar superconducting THz components to produce on-chip spectrometers with low to medium high resolution (R=5-1000) providing the capability to target any desired number of spectroscopic bands in each pixel in a 2D focal plane array with a huge reduction in cost, mass and volume over conventional technologies. MKID technology could therefore not only provide a dramatic increase in mapping speed for broad band imaging, it will also enable novel applications in spectroscopy. |
Cosmic Gamma-ray Background RadiationYoshiyuki InoueISAS, JapanTuesday, Nov 17, 2015AbstractThe cosmic gamma-ray background radiation is one of the most fundamental observables in the gamma-ray band. Although the origin of the cosmic gamma-ray background radiation has been a mystery for a long time, the Fermi gamma-ray space telescope has recently measured it at 0.1-820 GeV and revealed that the cosmic GeV gamma-ray background is composed of blazars, radio galaxies, and star-forming galaxies. However, Fermi still leaves the following questions. Those are dark matter contribution, origins of the cosmic MeV gamma-ray background, and the connection to the IceCube TeV-PeV neutrino events. In this talk, I will review our current understandings of the cosmic gamma-ray background and discuss future prospects of cosmic gamma-ray background radiation studies. |
Einstein's Legacy, and the Search for Gravitational WavesBruce AllenMax Planck Inst. for Grav. PhysicsTuesday, Nov 24, 2015AbstractEinstein's "general theory of relativity", the modern description of gravity, is his greatest legacy. Published exactly 100 years ago, it predicts the bending of light as it passes by the sun, and the collapse of stars into black holes. Another dramatic predictions is that rapidly accelerating massive objects produce ‘waves of gravitation’ that propogate through space at the speed of light. In the coming few years, a new generation of large ‘gravitational wave observatories’ promises to make the first direct detections of these waves. This will usher in a new way to ‘see' the universe and a new era in astronomy and astrophysics. |
X-ray reverberation mapping the inner accretion flow around supermassive black holesErin KaraUMDTuesday, Dec 1, 2015AbstractThe energy released from accretion on to a supermassive black hole has significant implications for the evolution of its host galaxy. Much of this energy is released in the form of radiation that is concentrated within a few tens of gravitational radii from the central black hole. Therefore studying the inner accretion flow—at the intersection of infall and outflow—is essential for understanding how the feedback mechanism works and the effect it will have on the surrounding environment. The aim of my research is to understand these extreme, relativistic environments through observations of X-ray reverberation mapping. Similar to Optical reverberation mapping, where time delays of days or weeks between the continuum and the emission lines from scattered light in Broad Line Region clouds map out kiloparsec scales, X-ray reverberation reveals time delays of tens of seconds, which map out microparsec scales in the accretion flow--well beyond the spatial resolution power of any instrument. This technique has just been discovered in the past 6 years, so in this talk I will give an overview of how the measurements are made, and the discoveries and advancements in this quickly developing field. I will show how reverberation is breaking degeneracies in our physical models and how it is helping us understand the geometry and kinematics of the inner accretion flow with unprecedented sensitivity. |
Searching for Vibrations from InflationJamie BockCaltechTuesday, Dec 8, 2015AbstractMoments after the Big Bang, our observable universe underwent a violent growth spurt called inflation. The inflationary expansion flung apart the observable universe from a causally-connected sub-atomic volume, and established a primordial spectrum of scalar perturbations that led to the temperature anisotropies observed in the cosmic microwave background. Our team has been making precise degree-scale polarization measurements of the CMB from the south pole with the BICEP/Keck series of experiments in search of a distinctive ‘B-mode’ pattern, a hallmark of tensor perturbations associated with a background of gravitational waves generated by inflation. I will present our latest results that incorporate multi-band information from the Planck satellite and new Keck Array data at 95 and 150 GHz. I will also discuss prospects from new data and improved measurements coming in the near future. |
NuSTAR Observations of Black Hole X-ray BinariesJohn TomsickBerkeleyTuesday, Dec 15, 2015AbstractThe Nuclear Spectroscopic Telescope Array (NuSTAR) is a SMEX mission that launched in 2012 and operates in the 3-79 keV bandpass. Although NuSTAR was primarily designed to provide improved hard X-ray (>10 keV) sensitivities and energy resolution for studying the Titanium-44 line at 68 keV, it has proved to be very useful for studying black hole X-ray binaries. For bright sources, the triggered readout of the NuSTAR detectors provides high throughput with no pile-up, and the detectors provide good energy resolution across the bandpass. For faint sources, the improved sensitivity has also provided results. I will present results from observations of several sources, focusing on (1) what determines the spectral state of the source? (2) what is the emission spectrum from the compact jet? and (3) the status of probing the immediate vicinity of the black hole, including progress on measuring black hole spins. |
Maxim Markevitch