KICP Seminars & Colloquia, Current and Future
Today's Seminar
Upcoming Seminars

Seminar schedule for Current (Fall 2017) & Future Quarters
September 27, 2017
Wednesday colloquium
Grayson C Rich
Triangle Universities Nuclear Lab
First observation of coherent elastic neutrino-nucleus scattering   [Abstract | Video]
September 29, 2017
Friday noon seminar
Francois Lanusse
Carnegie Mellon University
Machine Learning and Signal Processing for Weak Lensing Science: from galaxy image simulations to 3D mass maps   [Abstract]
September 29, 2017
Open Group seminar
Teresita Suarez Nogue
University College London
Large-scale fluctuations in the cosmic ionising background   [Abstract]
October 3, 2017
Astronomy Tuesday Seminar
Alison Coil
University of California, San Diego
Unconscious Bias: How It Works and How to Counter It   [Abstract | PDF]
October 4, 2017
Astronomy Colloquium
Alison Coil
University of California, San Diego
AGN-driven outflows at z~2   [Abstract]
October 6, 2017
Friday noon seminar
Adam Solomon
University of Pennsylvania
Aspects of field theory with higher derivatives   [Abstract]
October 9, 2017
Open Group seminar
Bohua Li
University of Texas at Austin
Cosmology in a University with Bose-Einstein-Condensed Scalar Field Dark Matter   [Abstract]
October 11, 2017
Wednesday colloquium
Joe Silk
IAP/JHU
The Limits of Cosmology   [Abstract | Video]
October 13, 2017
Friday noon seminar
Marko Simonovic
Institute for Advanced Study
Efficient Evaluation of Cosmological Statistics Using FFTLog   [Abstract]
October 18, 2017
Astronomy Colloquium
Gregg Hallinan
Caltech
Imaging All the Sky All the Time in Search of Radio Exoplanets   [Abstract]
October 24, 2017
Astronomy Tuesday Seminar
Lena Murchikova
Caltech
The first detection of warm ionized disk around the Galactic Center Black Hole SgrA*   [Abstract]
October 25, 2017
Wednesday colloquium
Josh Frieman
The University of Chicago
Probing Cosmology with the Dark Energy Survey   [Abstract | Video]
October 27, 2017
Friday noon seminar
Shunsaku Horiuchi
Virginia Tech
The status of sterile neutrino dark matter   [Abstract]
November 1, 2017
Astronomy Colloquium
Dan Hooper
University of Chicago
The WIMP is dead. Long live the WIMP!   [Abstract]
November 3, 2017
Friday noon seminar
Simone Ferraro
UC Berkeley
Surprises in the small scale CMB   [Abstract]
November 7, 2017
Astronomy Tuesday Seminar
Adrian Hamers
IAS
Hot Jupiters from Alternative High-eccentricity Migration Scenarios   [Abstract]
November 8, 2017
Wednesday colloquium
Lawrence M Krauss
Arizona State University
Journey to the Beginning of Time: Turning Metaphysics into Physics   [Abstract | Video]
November 10, 2017
Friday noon seminar
Stephen Feeney
Flatiron Institute
Clarifying the Hubble constant tension   [Abstract]
November 13, 2017
Open Group seminar
Nachiketa Chakraborty
Max-Planck-Institute fuer Kernphysik
Extreme Astrophysics with Novel Observables   [Abstract]
November 14, 2017
Astronomy Tuesday Seminar
Sumit Sarbadhicary
UPitt
The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys   [Abstract]
November 15, 2017
Astronomy Colloquium
Anatoly Spitkovsky
Princeton
Pulsar Magnetosphere: The Incredible Machine   [Abstract]
November 17, 2017
Friday noon seminar
Katelin Schutz
UC Berkeley
Excluding a thin dark matter disk in the Milky Way with Gaia DR1   [Abstract]
November 28, 2017
Astronomy Tuesday Seminar
Yong Zheng
Columbia
The Cycle of Gaseous Baryons between the Disk and Halo   [Abstract]
November 29, 2017
Astronomy Colloquium
Adam Burrows
Pennsylvania State University
Core-Collapse Supernova Explosion Physics   [Abstract]
December 6, 2017
Wednesday colloquium
TBA TBA
Latest Results from the Pierre Auger Observatory
December 8, 2017
Friday noon seminar
Ami Choi
The Ohio State University
Towards Accurate Cosmology with Galaxy Lensing Surveys
January 24, 2018
Wednesday colloquium
Silvia Galli
IAP
Cosmology results from Planck
February 7, 2018
Wednesday colloquium
Peter Adshead
University of Illinois at Urbana-Champaign
TBA
May 23, 2018
Wednesday colloquium
Brian Keating
UC San Diego
The Simons Observatory
 
WEDNESDAY COLLOQUIA
KICP Wednesday Colloquia: Unless otherwise noted, all talks are held in ERC 161 at 3:30 PM on Wednesdays. A reception will be held in the ERC 401 following the talk.

  • September 27, 2017 | 3:30 PM | ERC 161
    First observation of coherent elastic neutrino-nucleus scattering
    Grayson C Rich, Triangle Universities Nuclear Lab

    Video
    The process of coherent elastic neutrino-nucleus scattering (CEvNS) was predicted in 1974 by D.Z. Freedman, who suggested that attempts to detect CEvNS “may be an act of hubris” due to several profound experimental challenges. More than 40 years after its initial description, the world’s smallest functional neutrino detector has been used by the COHERENT Collaboration to produce the first observation of the process: a 14.6-kg CsI[Na] scintillator was deployed to the Spallation Neutron Source of Oak Ridge National Lab and observed, with high significance, evidence for a CEvNS process in agreement with the prediction of the Standard Model. I will discuss CEvNS and its connection to a range of exciting physics, including: its potential role in supernova dynamics; the possibility to use neutrinos as a tool for studying nuclear structure and neutron stars; its relationship to upcoming direct searches for WIMP dark matter; and the ways in which CEvNS could offer insight into physics beyond the Standard Model. The experimental program and the recent result from the COHERENT Collaboration will be presented along with ongoing efforts within the collaboration and future plans.
  • October 11, 2017 | 3:30 PM | ERC 161
    The Limits of Cosmology
    Joe Silk, IAP/JHU

    Image courtesy: J. Lazio
    Video
    One of our greatest challenges in cosmology is understanding the origin of the structure of the universe, and in particular the formation of the galaxies. I will describe how the fossil radiation from the beginning of the universe, the cosmic microwave background, has provided a window for probing the initial conditions from which structure evolved and seeded the formation of the galaxies, and the outstanding issues that remain to be resolved. I will address our optimal choice of future strategy in order to make further progress on understanding our cosmic origins.
  • October 25, 2017 | 3:30 PM | ERC 161
    Probing Cosmology with the Dark Energy Survey
    Josh Frieman, The University of Chicago

    Video
    I will overview the Dark Energy Survey (DES) project and highlight its early science results, focusing on the recently released cosmology results from the first year of the survey. The DES collaboration built the 570-megapixel Dark Energy Camera for the Blanco 4-meter telescope at NOAO's Cerro Tololo Inter-American Observatory in Chile to carry out a deep, wide-area, multi-band optical survey of several hundred million galaxies and a time-domain survey to discover several thousand supernovae. The survey started in Aug. 2013 and is now in its fifth observing season. DES was designed to address the questions: why is the expansion of the Universe speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? DES is addressing these questions by measuring the history of cosmic expansion and the growth of structure through multiple complementary techniques: galaxy clusters, the large-scale galaxy distribution, gravitational lensing, and supernovae, as well as through cross-correlation with other data sets. I will also discuss how the DES data are being used to make a variety of other astronomical discoveries, from the outer Solar System to ultra-faint dwarf galaxies to the kilonova counterpart of a binary neutron star gravitational-wave source.
  • November 8, 2017 | 3:30 PM | ERC 161
    Journey to the Beginning of Time: Turning Metaphysics into Physics
    Lawrence M Krauss, Arizona State University

    Video
    Even a generation ago, fundamental existential questions such as, "How did the Universe Begin?, How will it End?, Are we Alone, and, Are there OTHER Universes?," and other less grand but no less interesting questions such as "Do Black Holes Exist?" may have appeared as forever inaccessible metaphysical questions. Gravitational waves have now been discovered by LIGO, opening up a vast new window on the Universe. I will explain how we might eventually unambiguously detect a gravitational signal from moments after the Big Bang, pushing our direct empirical handle on the Universe back in time by 49 orders of magnitude, and revealing what we might learn about own origins, the nature of gravity, grand unification, and even the possible existence of other universes.
  • December 6, 2017 | 3:30 PM | ERC 161
    Latest Results from the Pierre Auger Observatory
    TBA TBA,
  • January 24, 2018 | 3:30 PM | ERC 161
    Cosmology results from Planck
    Silvia Galli, IAP
    Note: Reception at 4:30 PM in the ERC 401.
  • February 7, 2018 | 3:30 PM | ERC 161
    TBA
    Peter Adshead, University of Illinois at Urbana-Champaign
  • May 23, 2018 | 3:30 PM | ERC 161
    The Simons Observatory
    Brian Keating, UC San Diego
    Note: Reception at 4:30 PM in the ERC 401.

 
FRIDAY NOON SEMINARS
KICP Friday noon seminar: Unless otherwise noted, all talks are held in ERC 401 at Noon on Fridays.

  • September 29, 2017 | 12:00 PM | ERC 401
    Machine Learning and Signal Processing for Weak Lensing Science: from galaxy image simulations to 3D mass maps
    Francois Lanusse, Carnegie Mellon University

    The next generation of large-scale cosmological surveys, such as LSST, WFIRST and Euclid, aim at answering fundamental questions on the nature of dark energy and dark matter by measuring the weak lensing signal (gravitationally induced deformation of galaxy images) over large areas of the sky. In this talk, I will illustrate how the most recent advances in Machine Learning and Statistical Signal Processing open new perspectives for addressing some of the challenges faced by these new surveys as well as exploiting this wealth of data in new and exciting ways. In particular, I will focus on our work with Deep Generative Models in two different settings: simulating realistic galaxy images for shape measurement calibration purposes, and modeling the intrinsic alignment signal (the tendency of galaxies to align with the large scale structure) in hydrodynamical simulations, with the aim of producing realistic mock galaxy catalogs. Both of these applications aim to address some of the main systematics of future wide field lensing surveys. Finally, I will present an application of sparse signal processing which makes possible the reconstruction of high-resolution 3D weak lensing mass maps, with the ability to disentangle structures along the line of sight and resolve individual clusters.
  • October 6, 2017 | 12:00 PM | ERC 401
    Aspects of field theory with higher derivatives
    Adam Solomon, University of Pennsylvania

    I will discuss related aspects of field theories with higher-derivative Lagrangians but second-order equations of motion, with a focus on the Lovelock and Horndeski classes that have found use in modifications to general relativity. In the first half I will discuss how non-perturbative effects, like domain walls and quantum tunneling, are modified in the presence of these kinetic terms. In the second half I will investigate when restricting to such terms is and is not well-justified from an effective field theory perspective.
  • October 13, 2017 | 12:00 PM | ERC 401
    Efficient Evaluation of Cosmological Statistics Using FFTLog
    Marko Simonovic, Institute for Advanced Study

    The FFTLog algorithm can be seen as a way to decompose the linear power spectrum onto a basis of complex power-law functions. On the other hand, many important integrals in cosmology that involve power spectra have simple analytical solutions for a power-law universe. In this talk I will show how to combine these two ideas in practice. I will discuss applications to evaluation of the angular power spectrum and bispectrum of arbitrary observables, as well as evaluation of the loop integrals in cosmological perturbation theory of large-scale structure.
  • October 27, 2017 | 12:00 PM | ERC 401
    The status of sterile neutrino dark matter
    Shunsaku Horiuchi, Virginia Tech

    The sterile neutrino is a warm dark matter candidate with a host of observable signatures that have recently been sensitively tested. I will first review the sterile neutrino before introducing constraints arising from structure formation and high-energy astrophysics. These offer important complementarity in covering the sterile neutrino parameter space and I will highlight some of the recent rapid progress. I will also discuss ways forwards to test whether the 3.5 keV line detected in multiple dark matter concentrations may be arising from sterile neutrino dark matter.
  • November 3, 2017 | 12:00 PM | ERC 401
    Surprises in the small scale CMB
    Simone Ferraro, UC Berkeley

    Information about the late-time Universe is imprinted on the small scale CMB as photons travel to us from the surface of last scattering. Several processes are at play and small scale fluctuations are very rich and non-Gaussian in nature. I will review some of the most important effects and I will focus on the Sunyaev-Zel'dovich (SZ) effect and gravitational lensing. I will discuss how a combination of measurements can probe velocity fields at cosmological distances, inform us on cluster energetics and feedback processes, and detect the properties of patchy reionization. If time allows, I will describe new approaches to CMB lensing reconstruction on small scales.
  • November 10, 2017 | 12:00 PM | ERC 401
    Clarifying the Hubble constant tension
    Stephen Feeney, Flatiron Institute

    Hubble constant estimates from measurements of the local distance ladder and the cosmic microwave background (assuming a flat LCDM cosmology) are discrepant at the 2.8 to 3.4-sigma level. Interpreting this tension correctly requires a model-comparison calculation which depends strongly on the precise tails of the likelihoods in addition to the traditional ''n-sigma'' discrepancy. This model-comparison approach requires evaluation of the full distance-ladder likelihood, as opposed to a Gaussian or least-squares approximation to it. I will discuss our reframing of the distance ladder as a Bayesian Hierarchical Model (BHM), in which the Cepheids and supernovae (SNe) that comprise the ladder are fitted simultaneously and self-consistently. This highly flexible framework incorporates non-Gaussian anchor measurements, marginalizes over all relevant nuisance parameters and allows the use of heavy-tailed intrinsic scatter distributions to obtain robust inferences even in the presence of outliers, without resorting to unstable clipping methods. Using this BHM, I will clarify the Hubble constant tension by comparing LCDM to a model designed to predict the observed discrepancy.
  • November 17, 2017 | 12:00 PM | ERC 401
    Excluding a thin dark matter disk in the Milky Way with Gaia DR1
    Katelin Schutz, UC Berkeley

    If a component of the dark matter has dissipative interactions, it could collapse to form a thin dark disk in our Galaxy coincident with the baryonic disk. It has been suggested that dark disks could explain a variety of observed phenomena, including mass extinction events due to periodic comet impacts. Using the first data release from the Gaia space observatory, I will present the results of a search for a dark disk via its effect on stellar kinematics in the Milky Way. I will discuss our strong new limits that disfavor the presence of a thin dark matter disk and present updated measurements on the total matter density in the solar neighborhood.
  • December 8, 2017 | 12:00 PM | ERC 401
    Towards Accurate Cosmology with Galaxy Lensing Surveys
    Ami Choi, The Ohio State University

 
SPECIAL SEMINARS


 
OPEN GROUP SEMINARS

  • September 29, 2017 | 4:00 PM | ERC 419
    Large-scale fluctuations in the cosmic ionising background
    Teresita Suarez Nogue, University College London

    Effects of non-uniform cosmic ionizing background from quasars on statistics of the Ly alpha forest.
  • October 9, 2017 | 10:30 AM | ERC 419
    Cosmology in a University with Bose-Einstein-Condensed Scalar Field Dark Matter
    Bohua Li, University of Texas at Austin

    We consider an alternative to WIMP cold dark matter (CDM), ultralight bosonic dark matter (m≥10^-22eV) described by a complex scalar field (SFDM) with global U(1) symmetry, for which the comoving particle number density is conserved after particle production during standard reheating. We allow for a repulsive self-interaction. In a ΛSFDM universe, SFDM starts relativistic, evolving from stiff (w=1) to radiation-like (w=1/3), before becoming nonrelativistic at late times (w=0). Thus, before the familiar radiation-dominated era, there is an earlier era of stiff-SFDM-domination, during which the expansion rate is higher than in ΛCDM. SFDM particle mass m and coupling strength λ, of a quartic self-interaction, are therefore constrained by cosmological observables, particularly N_eff and z_eq. Furthermore, since the stochastic gravitational-wave background (SGWB) from inflation is amplified during the stiff era, it can contribute a radiation-like component large enough to affect these observables by further boosting the expansion rate. Remarkably, this same amplification makes detection of the SGWB possible at high frequencies by current laser interferometer experiments, e.g., aLIGO/Virgo and LISA. For SFDM particle parameters that satisfy these cosmological constraints, the amplified SGWB is detectable by LIGO for a broad range of reheat temperatures T_reheat, for values of tensor-to-scalar ratio r currently allowed by CMB polarization measurements. The SGWB is maximally detectable if modes that reentered the horizon when reheating ended have frequencies today in the LIGO sensitive frequency band. Upper limits on the SGWB reported by aLIGO O1 are used to place a new kind of cosmological constraint on SFDM. A wider range of SFDM parameters and T_reheat should be accessible to aLIGO/Virgo O5. For r=0.01 and λ/(mc^2)^2=10^-18 eV^-1 cm^3, 3σ detection is predicted for 600≤T_reheat(GeV)≤10^7 by O5.
  • November 13, 2017 | 3:00 PM | ERC 401
    Extreme Astrophysics with Novel Observables
    Nachiketa Chakraborty, Max-Planck-Institute fuer Kernphysik

    Despite intensive research, some fundamental properties of the most luminous particle accelerators and transients like AGNs, GRBs, etc. are unknown. Location and mechanisms of particle acceleration, connection to flaring and quiescent states, leptonic vs hadronic emission are open questions. Complexity of environments and processes make it hard to disentangle different scenarios. This suggests complementing conventional observables like the broadband spectrum with novel statistical observables like power spectral density (PSD) and the flux probability distribution (PDF) extracted from lightcurves, high and low energy polarisation, etc. While the PSD encodes the temporal structure of dynamical processes, particle acceleration and radiation and observing cadence, the PDF encodes the fundamental form of the emission processes (additive vs multiplicative). Polarised emission provides independent constraints on region geometry, magnetic fields, scattering processes, etc. to those from the above observables. These observables and related methods are also relevant for population studies. For e.g., time series methods used to compute the PSD, can be used in principle, estimate transient detection probability and resultant changes in source flux distribution, $frac{dN}{dF}$. A detailed theoretical framework capable of predicting these statistical observables from first principles in these sources is currently in nascency. Finally, they are complementary and potentially crucial crosschecks to neutrino and gravitational wave observations in the multi-messenger era. In this presentation, I demonstrate the potential of using such novel observables and related methods to probe physics of individual particle accelerators and the population at large by applying it to prominent blazars like Mrk 421, PKS 2155, etc.

 
THURSDAY LUNCH DISCUSSIONS
KICP's Thunch: KICP Cosmology Lunch (Thunch) Weekly on Thursdays, Noon, ERC 401A.

Please join us for an informal lunch discussion, led by KICP fellows, of recent news and papers in cosmology. Topics range from experiment and observations to theory in all areas of KICP science. To submit or view papers for this week's Thunch please visit the Thunch website.


 
ASTRONOMY COLLOQUIA
Colloquia of the Department of Astronomy & Astrophysics: Unless otherwise noted, all talks are held in ERC 161 at 3:30 PM on Wednesdays. A reception will be held in Hubble Lounge (ERC 501) following the talk.

  • October 4, 2017 | 3:30 PM | ERC 161
    AGN-driven outflows at z~2
    Alison Coil, University of California, San Diego

    AGN-driven outflows are assumed to be a key driver of galaxy evolution, determining the shape of the galaxy stellar mass function at high masses and regulating, perhaps even quenching, star formation as galaxies become quiescent. However, the details of how common this feedback is and how it impacts the host galaxy are generally unclear. I will present new results using Chandra data in the CANDELS and UltraVISTA surveys showing which galaxies host AGN of a given accretion rate and how this correlates with star formation in the host galaxy from z~0 to z~4. I will further present new results from the MOSDEF survey on AGN-driven outflows at z~2, discussing their incidence, kinematics, and physical extent. We find that fast, galaxy-wide AGN-driven outflows are common in typical star-forming galaxies at z~2 and that they likely help regulate star formation at the cosmic peak of galaxy growth.
  • October 18, 2017 | 3:30 PM | ERC 161
    Imaging All the Sky All the Time in Search of Radio Exoplanets
    Gregg Hallinan, Caltech

    All the magnetized planets in our solar system, including Earth, produce bright emission at low radio frequencies, predominantly originating in high magnetic latitudes and powered by auroral processes. It has long been speculated that similar radio emission may be detectable from exoplanets orbiting nearby stars, which would provide the first direct confirmation of the presence, strength and extent of exoplanetary magnetospheres, as well as informing on their role in shielding the atmospheres of potentially habitable exoplanets. Despite 4 decades of observations, no detection has been achieved. Surprisingly, however, brown dwarfs have been found to produce both radio and optical emissions that are strikingly similar to the auroral emissions from solar system planets, albeit 10,000 times more luminous, bolstering the continued search for similar emission from exoplanets. I will discuss the auroral radio emission from exoplanets and brown dwarfs and introduce a new radio telescope, consisting of 352 antennas spaced across 2.5 km, that images the entire viewable sky every ten seconds at low radio frequencies, thereby monitoring thousands of stellar systems simultaneously in the search for radio emission from exoplanets.
  • November 1, 2017 | 3:30 PM | ERC 161
    The WIMP is dead. Long live the WIMP!
    Dan Hooper, University of Chicago

    Although weakly interacting massive particles (WIMPs) have long been the leading class of candidates for the dark matter of our universe, the lack of a confirmed detection of these particles has left the community increasingly skeptical of their existence. In this talk, I will ask the following questions: How surprised should we be that WIMPs have not yet been detected? What assumptions might we change in order to explain the lack of any clear signals of dark matter? In light of the current experimental situation, what are the prospects for future direct, indirect and collider searches for dark matter? And lastly, may we already be observing evidence of annihilating WIMPs in the gamma-ray sky?
  • November 15, 2017 | 3:30 PM | ERC 161
    Pulsar Magnetosphere: The Incredible Machine
    Anatoly Spitkovsky, Princeton

    Pulsars are rotating magnetized neutron stars that emit repeating pulses of radiation spanning all of the electromagnetic spectrum. 50 years after their discovery, more than 2000 pulsars are known, and they have been used as sensitive astronomical probes of diverse phenomena ranging from the properties of interstellar medium to the predictions of general theory of relativity. Despite great observational successes, our theoretical understanding of how pulsar magnetospheres work is woefully incomplete. Pulsars bring together aspects of classical and quantum electrodynamics, coupled with strongly magnetized plasma physics in curved rotating spacetime of a massive compact object. The nonlinear interplay of these effects makes it a very difficult but rewarding problem to study. I will review the status and progress of pulsar magnetospheric modeling in various approximations, including force-free and relativistic magnetohydrodynamics, culminating with recent developments of fully kinetic simulations of pulsar magnetospheres. These simulations allow us to find the shape of the magnetosphere and the location of particle acceleration regions, constraining the origin of high energy emission. The pulsar magnetosphere is a prototype for other strongly magnetized astrophysical objects, and I will discuss how the lessons from pulsar modeling can be useful in understanding the physics of black hole disks and in predicting electromagnetic counterparts to gravitational wave sources.
  • November 29, 2017 | 3:30 PM | ERC 161
    Core-Collapse Supernova Explosion Physics
    Adam Burrows, Pennsylvania State University
    Note: Refreshments served at 4:45 PM, Hubble Lounge

    Core-collapse supernovae have challenged theorists and computational science for more than half a century. Such explosions are the source of many of the heavy elements in the Universe and the birthplace of neutron stars and stellar-mass black holes. However, determining the mechanism of explosion remains the key goal of theory. Recently, there have been breakthroughs in understanding and simulating these explosions, and I will describe our recent calculations that lead to robust explosions and the physics behind them. All these events have gravitational-wave and neutrino signatures that could be diagnostic of the internal dynamics of the mechanism and explosion phenomenology in real time. I will discuss such signatures and how their detection might bear on a definitive experimental resolution of the core-collapse puzzle.

 
ASTRONOMY TUESDAY SEMINARS

  • October 3, 2017 | 12:00 PM | ERC 576
    Unconscious Bias: How It Works and How to Counter It
    Alison Coil, University of California, San Diego

    PDF
    Unconscious or implicit bias is a preference for groups that operates outside of our awareness and is based on stereotypes or attitudes that we hold and have been taught. I will present results from a variety of studies that show how unconscious bias plays out, and how systemic it is, with a focus on academia. While I will mainly discuss faculty hiring, I will also touch on graduate admissions, review panels, recommendation letters, and interruptions during talks. I will discuss how the use of rubrics can help counter unconscious bias and other techniques to use when evaluating candidates.
  • October 24, 2017 | 12:00 PM | ERC 576
    The first detection of warm ionized disk around the Galactic Center Black Hole SgrA*
    Lena Murchikova, Caltech

    Image Credit Armitage and Christopher S. Reynolds, MNRAS, 341, 1041 (2003)
    The Milky Way's own supermassive black hole SgrA* is our best hope for studying black holes' immediate environments and their growth. There is a wide variety of accretion models, but the only thing we know with certainty is that the amount of the material around SgrA* is small and its accretion is very low. I report the first detection of the warm 10^4 K ionized disk within 0.015pc the black hole with recombination line of Hydrogen (n=31 -> 30 transition) with ALMA. I will discuss the disk dynamics, and describe our future observations making use of the close flyby of the S2 star by the galactic center in April 2018. We will be able to determine the presence of neutral hydrogen in the accretion zone and study the disk dynamics. Image Credit Armitage and Christopher S. Reynolds, MNRAS, 341, 1041 (2003)
  • November 7, 2017 | 12:00 PM | ERC 576
    Hot Jupiters from Alternative High-eccentricity Migration Scenarios
    Adrian Hamers, IAS

    One of the proposed formation origins of hot Jupiters (HJs) is high-eccentricity (high-e) migration. In high-e migration, the eccentricity of the orbit of a planet initially beyond the ice line is dynamically excited, leading to strong tidal dissipation occurring near periapsis and eventually resulting in a tight orbit. Previously-studied secular variants of high-e migration involve an inclined and/or eccentric binary companion (star or massive planet). However, the predicted formation rates are too low compared to observations, by a factor of ~ 10. Therefore, alternative scenarios are needed. Recently, an alternative scenario was proposed by Lithwick & Wu involving secular chaos with three or more planets. This scenario can potentially produce many HJs because the initial conditions to achieve high eccentricities are less stringent compared to the case of an inclined binary companion. Until recently, studies of this scenario were limited to small phase space due to the prohibitive nature of direct N-body integrations. Here, we use a new secular method to study the formation of HJs driven by secular chaos in multiplanet systems. Also, we consider scenarios in which HJs are formed through high-e migration in stellar triple systems, and discuss how secular evolution suggests the presence of unseen planetary companions to hot Jupiters in stellar binaries. Lastly, we briefly discuss the possibility of forming HJs through encounter-driven high-e migration in dense stellar systems like globular clusters.
  • November 14, 2017 | 12:00 PM | ERC 576
    The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys
    Sumit Sarbadhicary, UPitt

    Our understanding of the progenitors of many stellar species, such as supernova, massive stars, and low mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. A critical reappraisal of stellar evolution theories is therefore in order. In this talk, I will discuss a method to recover delay-time distributions (DTDs) - the hypothetical rate of occurrence of an object vs time since a brief burst of star formation - which can pose powerful observational constraints on stellar evolution timescales for progenitor models of various stellar objects. To calculate DTDs, one needs a catalog of objects and a map of the star-formation histories of the host galaxy. The technique is particularly effective in the Local Group, where reliable star-formation histories from resolved stellar populations, and high quality surveys are available. I will discuss the application of this method to pulsating variable stars like RR Lyrae and Cepheids. I will also discuss my progress towards calculating a supernova (SN) DTD from Local Group supernova remnants, with the hope of constraining the long-standing progenitor problems of thermonuclear and core-collapse SNe, and quantifying momentum feedback from supernovae in nearby galaxies.
  • November 28, 2017 | 12:00 PM | ERC 576
    The Cycle of Gaseous Baryons between the Disk and Halo
    Yong Zheng, Columbia

    The disks of galaxies closely interact with their circumgalactic media (CGM) through the disk-halo interfaces. The disks grow by inflows from the CGM, while the CGM is enriched, stirred, and heated by outflows from the disks. Recent years have seen great breakthroughs in observations of the inflows/outflows at the disk-halo interfaces; however, inflow detections are still rare and the structure of the disk-halo interface is unclear. In my talk, I will first show HST/COS observations of ionized gas inflows at M33s disk-halo interface, which is among the first to unambiguously reveal the existence of disk-wide galactic inflows. Then I will present a 3D kinematic model of the disk-halo interface of the Milky Way (MW), which incorporates co-rotation, halo lagging, inflow, and turbulence broadening. I will show that the MW's low-velocity (|v|<100 km/s) ionized gas contents seen toward background quasars are not only from its interstellar medium and disk-halo interface; there is a significant fraction (~70%) of gas contributed by the MW's CGM moving at low velocities. Order-of-magnitude estimates on the mass of the low-velocity MW's CGM suggest that the MW's CGM may be as massive as those of L~L* star-forming galaxies at z~0.2.

 
ASTRONOMY SPECIAL SEMINARS