|2016, Fall||2016, Spring|
|2015, Fall||2015, Spring|
|2014, Fall||2014, Spring|
|2013, Fall||2013, Spring||2013, Summer|
|2012, Fall||2012, Spring|
|2011, Fall||2011, Spring|
|2010, Fall||2010, Spring|
|Aug 30||Tom Brown (STScI) - "The Quenching of the Ultra-faint Dwarf Galaxies in the Reionization Era"|
|Sep 6||No Colloquium|
|Sep 13||Special Location: B34, W120A+B
Rodolfo Montez (SAO) - "Insights into Binary Stars, Stellar Winds, and Astrophysical Plasmas from X-ray Observations of Planetary Nebulae"
|Sep 19||Special Date
Joseph Howard (GSFC) - "Freeform Optics at NASA"
|Sep 20||No Colloquium|
|Sep 27||Special Location: B34, W120
Mateusz Ruszkowski (Michigan) - "The role of cosmic rays in stellar and supermassive black hole feedback"
|Oct 4||Maria Petropoulou (Purdue) - "What is the contribution of blazars to the IceCube neutrino flux?"|
|Oct 11||Matthew Baring (Rice) - "Blazar and accretion science" (tentative)|
|Oct 18||Jonathan Arenberg (Northrop-Grumman) - "Lessons from Chandra" (tentative)|
|Nov 1||Dominik Riechers (Cornell) - "Cold gas in high-z galaxies with ALMA" (tentative)|
|Nov 8||Brian Metzger (Columbia) - "Gravitational waves and GRB" (tentative)|
|Nov 15||Tetsu Kitayama (Toho Univ.) - ALMA observations of SZ effect in galaxy clusters (tentative)|
|Nov 29||Special Location: B34, W120
Brian Grefenstette (Caltech) - "NuSTAR observations of SNRs and the Sun" (tentative)
|Dec 6||David Spergel (Princeton) - "WFIRST" (tentative)|
|Dec 13||Tom Barclays (NASA Ames) - Kepler Earth-sized planets (tentative)|
|Dec 20||Ryan Chornock (Ohio U.) - Time-domain astrophysics (tentative)|
|Dec 27||No Colloquium|
The Quenching of the Ultra-faint Dwarf Galaxies in the Reionization Era
Tuesday, Aug 30, 2016
I will present results from a Hubble Space Telescope survey of the ultra-faint dwarf galaxies. These Milky Way satellites, discovered in the Sloan Digital Sky Survey, appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in the efforts to understand the missing satellite problem. Because they are the least luminous, most dark matter dominated, and least chemically evolved galaxies known, the ultra-faint dwarfs are the best candidate fossils from the early universe. The primary goal of the survey is to measure the star-formation histories of these galaxies and discern any synchronization due to the reionization of the universe.
Insights into Binary Stars, Stellar Winds, and Astrophysical Plasmas from X-ray Observations of Planetary Nebulae
Tuesday, Sep 13, 2016
Planetary nebulae (PNe) provide textbook examples of astrophysical plasma and shock processes and provide essential constraints for theories of stellar evolution and the chemical enrichment of the universe. The varied shapes of PNe reveal the actions of interacting stellar winds from the late stages in the life of intermediate-mass stars, and growing evidence suggests that many PNe are the products of interacting binary star systems. As a result, studies of PNe can yield insight into other astrophysical objects governed by binary processes, such as, low mass X-ray binaries and Type Ia supernovae. Best known for their ten thousand degree optical line emission, the Chandra X-ray Observatory has established that a fraction of PNe display extended X-ray emission from shock-heated plasmas of a few million degrees and that the central stars harbor hotter than expected point-like emission from plasmas that reach tens of millions of degrees. I describe the discoveries, insights, and questions raised by Chandra observations of PNe with emphasis on those results gleaned from the Chandra Planetary Nebulae Survey (ChanPlaNS), which is the first systematic X-ray survey of PNe in the solar neighborhood.
Freeform Optics at NASA
Monday, Sep 19, 2016
Freeform optics are non-rotationally symmetric optics with large departures from a base sphere, typically from many microns to mm. They provide additional degrees of freedom to optical designs, which enable instruments with better image quality, larger fields of view, and smaller package size. The past, present, and future usage of Freeform Optics at NASA are discussed in this presentation.
The role of cosmic rays in stellar and supermassive black hole feedback
Tuesday, Sep 27, 2016
I will discuss the role of cosmic rays in stellar and supermassive black hole feedback. I will argue that cosmic rays are likely to play a very important role across a large range of distance scales -- from the scales of individual galaxies to the scales comparable to those of cool cores of galaxy clusters.
Regarding the galactic scale feedback, I will focus on supernova and cosmic ray driven winds. Galactic outflows play an important role in galaxy evolution and, despite their importance, detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. Although cosmic rays comprise only a tiny fraction of interstellar particles by number, they carry energy comparable to that in the thermal gas. I will describe a suite of global 3D MHD numerical simulations that focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of cosmic ray streaming along the magnetic fields. Our results show that this microphysical effect can have a significant impact on the wind launching depending on the details of the plasma physics.
Regarding the feedback on galaxy cluster scales, I will discuss results from our simulations of black hole jets in cool cores of galaxy clusters including the effects of cosmic rays. I will argue that cosmic ray heating of the intracluster medium (ICM) may be a very important heating mechanism both in the tenuous and cold phases of the ICM while not violating observational constraints.
While largely an unexplored territory in the context of galactic winds and AGN feedback, cosmic ray feedback is an important process facilitating launching and efficient driving of galactic-scale winds in starburst galaxies and heating of the ICM and remains the subject of intense research.
What is the contribution of blazars to the IceCube neutrino flux?
Tuesday, Oct 4, 2016
The discovery of 0.1 – 2 PeV neutrinos of astrophysical origin by IceCube has opened a new window in the high-energy Universe. There are various astrophysical candidate sources, including active galactic nuclei (AGN) and starburst galaxies. Although a firm association of the detected neutrinos with one (or more) of them is still lacking, IceCube has started constraining various theoretical models. In this talk, I will present our model predictions for (i) the blazar contribution to the diffuse neutrino flux and (ii) for the possibility of detecting individual blazars as neutrino point sources. I will discuss the implications of the latest IceCube searches on the theoretical models for blazar emission.