Updated: 17 March 2016

MIT Kavli Institute for Astrophysics and Space Research

2016 Postdoctoral Symposium

April 27-29, 2016, 11:45am−1:30pm in 37-252 (Marlar Lounge)

This annual event features the MKI-affiliated postdocs presenting 25 minute talks (with 5 minutes of questions) on their past, present, and/or future research to the MKI community.

Lunch will be provided, and the talks will promptly begin at noon.

SOC: Joey Neilsen, Paul Torrey, Olek Sadowski

LOC: Debbie Meinbresse

Event generously supported by the MKI Kavli Institute for Astrophysics and Space Research.

Speaker Schedule

Wednesday, April 27, 2016, 12pm

Moderator: Olek Sadowski

Speaker: Rongmon Bordoloi
Title: Mapping the Nuclear Outflow of the Milky Way: The Kinematics and Spatial Extent of the Fermi Bubbles.
Abstract: Recent observations of gamma rays together with microwaves and polarized radio waves, have detected giant lobes of plasma (Fermi Bubbles) extending above and below the Galactic plane of the Milky Way. These are possible signs of a Nuclear wind powered by either the central black hole or concentrated nuclear star-formation; but our understanding of their origin is hampered by a lack of kinematic information. I will report new observations from a systematic, absorption-line survey that maps the spatial and kinematic properties of the biconical nuclear outflow, using UV spectroscopy of AGN and halo stars lying close on the sky to the Galactic Center. The variation in absorption properties with Galactic latitude allows us to constrain the physical conditions in the outflowing gas. The observed kinematics of absorption components will be discussed and compared to predictions from biconical outflow models. I will show that the observed absorption profiles can be explained by a biconical nuclear wind with a radial velocity of ~ 1000 km/sec, and constrain the kinematic age of the Fermi Bubbles to be ca. 6-9 Myrs. Using these estimates, I will constrain the minimum mass of UV absorbing gas entrained in the Fermi Bubbles. These observations illustrate the novel use of UV spectroscopy to constrain the feedback processes that regulate galaxy evolution.

Speaker: Rana Ezzeddine
Title: Atmospheric modeling and abundance determination in ultra-metal-poor stars
Abstract: In the era of large-scale spectroscopic surveys (such as Gaia-ESO, SDSSIII-APOGEE, RAVE, ...) aiming to trace and untangle the history of stellar populations and the Galaxy, an important need to characterize in details the chemical composition of stars with the highest accuracies possible, has arisen. The most primitive metal-poor stars especially are important for studying the conditions of the early Galaxy and are also relevant to big bang nucleosynthesis. In my talk I will describe the different methods used to model cool stellar atmospheres and highlight their important implications on the abundance and parameter determination of metal-poor stars.

Speaker: Meng Su
Title: From Microwave to Gamma ray: Future CMB Telescopes in Tibet and the First Chinese Astronomy Satellite DAMPE
Abstract: Space gamma-ray astronomy was born at MIT more than half century ago. A few gamma-ray satellites operated since then, in particular the most recent Fermi Gamma-ray Space Telescope, have proved the great potential of studying astrophysics, cosmology, and fundamental physics through the gamma-ray sky. I will talk about the recently launched DAMPE, the very first Chinese astronomy satellite, and the planned gamma-ray missions including HERD and PANGU. Together with the next generation of ground-based Cherenkov telescopes e.g. CTA and LHAASO, we will be able to measure gamma-ray photons/cosmic rays with energies across nine decades of energies from MeV to above PeV with much improved sensitivity. Finally, I briefly introduce my recent effort to build future CMB telescopes at the Ali Observatory in Tibet, in order to cover the northern CMB sky.

Thursday, April 28, 2016, 12pm

Moderator: Joey Neilsen

Speaker: Niels Warburton
Title: Inspiral into Gargantua
Abstract: We model the inspiral of a compact object into a more massive black hole rotating very near the theoretical maximum. We find that once the body enters the near-horizon regime the gravitational radiation is characterized by a constant frequency, equal to (twice) the horizon frequency, with an exponentially damped profile. This contrasts with the usual "chirping" behavior and, if detected, would constitute a "smoking gun" for a near-extremal black hole in nature.

Speaker: Monica Turner
Title: Hydrogen and metal-line absorption around high-redshift galaxies
Abstract: Studying the exchange of gas between galaxies and their environments is integral to our understanding of galaxy formation and evolution. Since most of this gas is too diffuse to detect in emission, we use ultra-luminous QSOs to probe gas in absorption along the line-of-sight to galaxies. However, at the epoch of the peak star-formation rate of the universe (z~3), the observations are hampered by the density of the Lyman alpha forest, which makes the identification of individual absorption lines prohibitively difficult. To combat this, we use a method known as "pixel optical depth", which can quickly and objectively be applied to many spectra, and facilitates comparison to cosmological simulations. I will discuss work done using this method for both current and future high-redshift galaxy surveys.

Speaker: Zach Berta-Thompson
Title: Our First Chance to Study the Atmosphere of a Rocky Exoplanet
Abstract: I will present our recent discovery of an Earth-size planet transiting a nearby M dwarf star, and describe our ongoing efforts to observe its atmosphere with Magellan and Hubble.

Friday, April 29, 2016, 12pm

Moderator: Paul Torrey

Speaker: Rahul Kannan
Title: Effect of anisotropic thermal conduction on the properties of galaxy clusters.
Abstract: We use high resolution cosmological simulations to simulate and quantify the effect of thermal conduction in clusters. These simulations show that conduction effectively couples with the black hole feedback and evaporates the cool-core in the center. The existence of temperature features in the ICM even with conduction turned on, shows that it is possible for cold fronts and sharp temperature gradients to survive in a conducting medium if the magnetic fields are draped around the cold pockets in the ICM. The magneto-thermal instability drives turbulence within the ICM which transports gas from the center of the clusters to the outskirts, consequently making the metallicity profile flatter. We conclude that thermal conduction does change the global properties of galaxy clusters even if the effective conductivity is suppressed below the Spitzer-Braginskii value.

Speaker: Esra Bulbul
Title: A Case for the 3.55 keV Line: Claims, Counterclaims, Reasons, and Evidence
Abstract: X-ray observations of dark matter dominated objects have the potential to reveal a signal from decaying or annihilating dark matter. We previously reported the detection of an unidentified emission line at 3.55 keV in the stacked XMM-Newton observations of galaxy clusters. The origin of this unidentified line could be attributed to decay of dark matter particles. I will provide a comprehensive review on the detections and non-detections of the 3.55 keV line in dark matter dominated objects in the literature.

Speaker: Olek Sadowski
Title: Low-luminosity black hole accretion flows and the state transitions
Abstract: I will present a novel algorithm that allows for simultaneous evolution of a two-temperature gas and radiation field, which allows for the first time to self-consistently study accretion floes in the intermediate regime, relevant to state-transitions in X-ray binaries and low-luminosity AGN. Preliminary results will be presented.