January 10, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium From Emergent Gravity to Dark Energy and Dark Matter Erik P. Verlinde, University of Amsterdam
Video The observed deviations from the laws of gravity of Newton and Einstein in galaxies and clusters can logically speaking be either due to unseen dark matter or due to a change in the way gravity works. Until recently there was little reason to doubt that general relativity correctly describes gravity in these circumstances. In the past few years insights from black hole physics and string theory have lead to a new theoretical framework in which the gravitational laws are derived an underlying microscopic quantum description of spacetime. An essential ingredient in the derivation of the Einstein equations is that the quantum entanglement of the vacuum obeys an area law, a condition that is known to hold in Anti-de Sitter space. In a Universe that is dominated by positive dark energy, like de Sitter space, the microscopic entanglement entropy contains, in addition to the area law, a volume law contribution whose total contribution equals the Bekenstein-Hawking entropy associated with the cosmological horizon. We will argue that this extra volume law contribution leads to modifications in the emergent laws of gravity, and provide evidence for the fact that these modifications explain the observed phenomena in galaxies and clusters currently attributed to dark matter. We end with a discussion of the possible implications for early cosmology, the CMB and structure formation.
January 17, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium WFIRST: Where Things Stand with the First Exoplanet Direct Imaging Flight Mission Maggie Turnbull, SETI
The WFIRST mission will be the first demonstration of exoplanet coronagraphy in space, and is intended to demonstrate several key technologies that are on the critical path to larger missions that will eventually find and spectrally characterize planets that could be habitable to life as we know it. WFIRST entered Phase A in January of 2016, and is expected to enter Phase B in April of this year. This talk will describe the entertaining story of how this mission came to be, where things currently stand in terms of predicted imaging performance, the potential for a starshade rendezvous mission, and what to expect for guest observer opportunities. I'll also describe how the two coronagraph science teams are working to maximize the scientific output of what is categorized as a "technology demonstration" instrument. Finally, I'll offer some of my personal take-aways from the experience of watching such a large and challenging mission come together.
January 24, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Citizen Science Frontiers: Efficiency, Engagement, and Serendipitous Discovery with Human-Machine Systems Laura Trouille, The Adler Planetarium and Northwestern University
Video The Zooniverse is the world's largest and most successful scientific crowdsourcing platform, engaging more than 1.6 million volunteers in tasks including classifying galaxies, discovering planets, transcribing artist's notebooks, and tracking resistance to antibiotics. Processing our increasingly large datasets poses a bottleneck for producing real scientific outcomes. Citizen science - engaging the public in research - provides a solution, particularly when coupled with machine learning algorithms and sophisticated task allocation. Faced with a rapidly growing demand for citizen science projects, Zooniverse launched its 'Project Builder' which allows you, the researcher, to build your own project in-house for free using the Zooniverse infrastructure and tools. In this talk I will discuss the frontiers of citizen science, including Zooniverse innovations in human-machine integration coupled with community engagement -- and the related open questions. I will also provide a brief tutorial on building your own crowdsourcing project.
January 31, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium The Basis for Cosmic Ray Feedback Ellen Zweibel, University of Wisconsin-Madison
There is strong observational and theoretical evidence that star formation in galaxies is inherently self limiting, and that the interaction of galaxies with their environments plays a significant role in galactic evolution. Cosmic rays - the relativistic particles that pervade our galaxy and account for about 1/3 of the energy density in the interstellar medium - have emerged as a likely agent of these forms of feedback. The basis of cosmic ray feedback is scattering of cosmic rays by plasma waves, a microscale process that ultimately transfers energy and momentum between cosmic rays and thermal gas. The image, from Ruszkowski, Yang, & Zweibel 2017, shows a simulation of an outflow driven from a galaxy by this process.
February 14, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Galactic Winds: Phenomenology, Physics, and Implication Tim Heckman, Johns Hopkins University
I will discuss the nature of galactic winds driven by the energy and momentum supplied by populations of massive stars. I will give an overview of the basic physical processes that lead to the formation and propagation of galactic winds. I will then give a "guided tour" of the multi-phase galactic wind driven by the prototypical starburst galaxy M 82. Next, I will describe how the basic parameters of winds can be inferred from the data and summarize the systematic dependences of these parameters on the key properties of the galaxy and the starburst. I will then discuss how well these systematic properties compare to assumptions used in cosmological simulations of galaxy evolution. Finally, I will describe the implications of winds for galaxy evolution, specifically in the context their impact on the circum-galactic medium and on the chemical evolution of galaxies.
February 21, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Discovering the Highest Energy Neutrinos Using a Radio Phased Array Abby Vieregg, The University of Chicago
Video Ultra-high energy neutrino astronomy sits at the boundary between particle physics and astrophysics. The detection of high energy neutrinos is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. IceCube has detected astrophysical neutrinos at lower energies, but the best limit to date on the flux of ultra-high energy neutrinos comes from the ANITA experiment, a NASA balloon-borne radio telescope designed to detect coherent radio Cherenkov emission from cosmogenic ultra-high energy neutrinos. The future of high energy neutrino detection lies with ground-based radio arrays, which would represent an large leap in sensitivity. I will discuss a new radio phased array design that will improve sensitivity enormously and push the energy threshold for radio detection down to overlap with the energy range probed by IceCube.
February 28, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Heavy element synthesis in the Universe Enrico Ramirez-Ruiz, University of California, Santa Cruz
The source of about half of the heaviest elements in the Universe has been a mystery for a long time. Although the general picture of element formation is well understood, many questions about the nuclear physics processes and particularly the astrophysical details remain to be answered. Here I focus on recent advances in our understanding of the origin of the heaviest and rarest elements in the Universe.
March 7, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Origins of Super-Earths in Inner Solar Systems Bekki Dawson, Pennsylvania State University
Origins of Super-Earths in Inner Solar Systems
Over the past decade, exoplanet surveys have discovered that many other solar systems teem with super-Earths on sub-Mercury orbits. A major open question is whether these super-Earths formed on their observed close-in orbits or formed at a wider separations and migrated in. I will present recent work on what the orbital and compositional properties of super-Earths in inner solar systems can reveal about super-Earths' origins and more generally about the physical processes driving the formation and evolution of planetary systems.
March 14, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Dark Matter in the Universe Katherine Freese, University of Michigan
Video "What is the Universe made of?" This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.
January 12, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Topics in weak lensing Patricia Larsen, Argonne National Laboratory
Gravitational weak lensing has emerged in recent years as a powerful probe of cosmology, giving important constraints on both dark and luminous matter. This has led to a number of ambitious future surveys, which promise to revolutionise the field if theoretical challenges can be met. In this talk I will discuss some of my recent work in the field of weak lensing, spanning a range of topics including combined probe analysis, intrinsic alignment contamination and delensing.
January 19, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Discussion on old and new mechanisms of leptogenesis Jessica M Turner, Fermi National Accelerator Laboratory
In the first half of the talk, I will present preliminary results which indicate the scale of thermal leptogenesis may be several orders of magnitude lower than previously thought.
In the second half of this talk I will present a mechanism of leptogenesis which is based on the vacuum CP-violating phase transition. This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This
mechanism provides strong connections with low-energy neutrino experiments.
January 26, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Mass' not the only thing: Secondary effects in the galaxy-halo connection Yao-Yuan Mao, University of Pittsburgh
Dark matter halos are the building blocks of our universe. The story we have been telling is that the galaxies live in halos, and that brighter galaxies live in bigger halos. This story is mostly consistent with our observation and hydrodynamical simulations, and has shed light on our understandings of galaxy formation and evolution. However, it is also clear that this simple, zeroth-order galaxy-halo connection is not the whole story. The assembly history of halos affects the galaxies reside in, and also affects the clustering properties of halos. This effect, usually known as "assembly bias," has brought new challenges to our ability to accurately model the galaxy-halo connection. A class of galaxy-halo connection models that take assembly bias into account has emerged, but it at the same time highlights the complex nature of assembly bias. In this talk I will discuss a few different aspects of assembly bias, focusing on how it affects the galaxy-halo connection and also its implications.
February 2, 2018 | 12:00 PM | ERC 401 | Friday noon seminar High redshift 21cm intensity mapping Past, Present, and Future Daniel Jacobs, Arizona State University
The redshifted 21 cm line from neutral hydrogen provides a direct, cosmological scale, probe of the epochs of reionization and heating. In the past decade, multiple experimental arrays have worked towards detection and characterization of this spectral line signal at redshifts 6 and higher. HERA is a second generation instrument probing 21cm emission and absorption at redshifts from 6 to 20. The use of large static dishes provides sensitivity which is predicted to be roughly an order of magnitude larger than first generation experiments while advances in instrumentation and technique aim for reduced foreground contamination. The raw sensitivity provided by dishes is high enough that forecasts of astrophysical parameter constraint precision is limited mainly by model uncertainty not sensitivity, and that for the first time direct imaging of features is theoretically possible. HERA is proceeding with construction while observing in parallel with new dishes being added as they become available. The 2017-2018 observing season with 40 dishes is forecasted to have roughly double the sensitivity of previous experiments. Here we report the ongoing commissioning of this array and present early results of experiments in calibration and imaging.
February 9, 2018 | 12:00 PM | ERC 401 | Friday noon seminar The impact of massive neutrinos on cosmological observables Francisco Villaescusa-Navarro, Center for Computational Astrophysics
Neutrinos are one of the most mysterious particles in nature. The discovery that they are massive has revolutionized our understanding of fundamental physics. Unfortunately, we still don't know their nature, masses or hierarchy. A worldwide effort is underway trying to answer these questions through laboratory experiments. In this seminar I will show how neutrino's unique nature leaves signatures on many different cosmological observables such as the properties of matter, halos, galaxies, voids, redshift-space distortions, the Lya-forest, baryonic acoustic oscillations and 21cm. I will discuss how those signatures can be used to weigh neutrinos and what are the main problems to obtain an unbiased measure of their masses.
February 16, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Project 8: Towards a Direct Measurement of the Neutrino Mass with Tritium Beta Decays Noah S Oblath, Pacific Northwest National Laboratory
Cyclotron Radiation Emission Spectroscopy, a frequency-based method for deter- mining the energy of relativistic electrons, has recently been demonstrated by the Project 8 collaboration. Applying this technique to the tritium endpoint provides a new avenue for measuring the absolute mass-scale of the neutrino. The proof of principle was done in a small waveguide detector using gaseous 83mKr as a source of monoenergetic electrons. As the next step towards a neutrino mass measurement, we are upgrading the existing detector to operate using a molecular tritium source, and to have enhanced radiofrequency properties. These upgrades are the next research and development steps needed to design a larger scale experiment that will approach the existing neutrino mass limits. I will discuss the expected physics reach of this second phase of Project 8 with molecular tritium, based on data from its commissioning with 83mKr. I will also present the plans for Phases III and IV, and the challenges being addressed for each phase.
March 2, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Innovations in Big Data and HPC for Cosmology Deborah Bard, NERSc, LBNL
Cosmological ''big data'' problems go beyond the simple volume of data stored on disk. Our observations of the universe are necessarily finite, and the challenge we face is how we can extract the maximum amount of information from the observations and simulations we have available to us.
High Performance Computing (HPC) is increasingly being used to enable complex analyses that were previously inaccessible to scientists. NERSC is the mission computing center for the DOE Office of Science, and we sit at the intersection of HPC, algorithmic development and cutting-edge science. I will discuss some of the cosmology projects we lead in this space, such as Galactos (calculating the anisotropic three-point correlation function for 20 billion galaxies), Celeste (cataloguing the visible universe through Bayesian inference using Julia), CosmoGAN (developing a cosmological emulator using generative adversarial networks) and CosmoFlow (learning the structure of the universe through 3D deep learning techniques).
These projects showcase a combination of computer science, HPC advances and real problems in cosmology, with the overarching theme of how we can scale computing tools (including machine learning and inference) to enable new techniques in data analysis, and to accelerate time-to-discovery.
January 16, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Surveying Spotted Stars with Photometric, Spectroscopic, and Interferometric Observations Rachael Roettenbacher, Stockholm University
For stars with convective outer layers, stellar magnetism manifests as dark starspots -- localized regions of stifled convection. Starspots affect measurements of fundamental stellar parameters, including temperature and radius, which lead to inaccurate estimates of age and mass. Additionally, starspots have been shown to mimic and obscure detections of planets. By imaging stellar surfaces, we begin to disentangle the signatures of stellar magnetism. The imaging efforts discussed here feature aperture synthesis imaging using interferometric data collected with the Michigan Infrared Combiner (MIRC) at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array with sub-milliarcsecond resolution. We characterize active RS CVn binary systems and detect magnetic structures across the surface of the giant primary stars. We compare the results to simultaneous Doppler and light curve inversion imaging. The observed global regions of suppressed convection likely affect stellar parameter estimates by altering the structure of the photosphere. Extensions of this study will survey spotted stars in order to understand how stellar magnetism affects stellar parameters, impacts the evidence of companions and their characterization, accounts for long-term changes in the flux of active stars, and differs from the Sun for stars with large convective envelopes.
January 30, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar The deaths of galaxies and the growth of supermassive black holes: implications for galaxy evolution and tidal disruption events Decker French, Carnegie Observatories
Post-starburst (or "E+A") galaxies are in transition between star-forming galaxies and early-types, and represent a clear path for galaxies to transform from star-forming to quiescence. Many show signs of a recent galaxy-galaxy merger and a newly-evolved stellar bulge, and most have LINER-like emission, which may indicate low luminosity AGN activity. Thus, the study of this short-lived phase of galaxy evolution can address the connections among mergers, star formation history, and the evolution of the nucleus as a galaxy evolves onto the red sequence. Surprisingly, we have discovered that many these galaxies have significant reservoirs of molecular gas, yet low dense gas fractions. We have also found that post-starburst galaxies host a disproportionate number of Tidal Disruption Events, in which a star is accreted onto the black hole. The recent starburst in these galaxies allows us to put strong constraints on the details of their recent star formation histories, and to place them on a timeline post-burst. I will discuss these results and other new work detailing how their stellar populations, gas content, and black hole properties evolve.
February 13, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Relativistic Jets: Particle Accelerators of the Universe Maria Petropoulou, Princeton University
The image shows an artist impression of the quasar ULAS J1120+0641
Image credit: ESO/M. Kornmesser
Relativistic jets, i.e., collimated outflows of plasma traveling with speeds approaching the speed of light, are ubiquitious in the Universe. They are unique laboratories for studying the physics of magnetized plasmas, particle acceleration, and radiation processes in extreme conditions that can never be achieved with terrestrial experiments. Some of the most powerful astrophysical jets are those emerging from the centers of active galaxies (AGN). It is commonly accepted that AGN jets can accelerate particles to ultra-relativistic energies which then radiate up to TeV energies. Yet, there are many unresolved issues with this well established paradigm: How is the jet energy converted into radiation? Are the radiating particles electrons or protons? Where and how are these particles accelerated? In this talk, I will discuss how we can combine multiple messengers, such as photons and neutrinos, with state-of-the-art numerical simulations to obtain insights into the physical processes operating in relativistic jets. The image shows an artist impression of the quasar ULAS J1120+0641 Image credit: ESO/M. Kornmesser
February 20, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Making a Universe with Axions and Inflatons Chanda Prescod-Weinstein, University of Washington
How can new approaches to quantum fields illuminate astrophysics on all scales? The discovery of the Higgs boson reinforces the possibility that other similar, scalar particles may exist in nature and could drive cosmological inflation. In this talk, I will discuss one such dark matter and sometime inflaton candidate, the axion. I will talk about the increasingly popular claim that dark matter axions form an exotic state of matter called a Bose-Einstein condensate and my own work on this idea. This unique intersection of early universe cosmology with an idea from atomic physics is but one example of the exciting ways in which we are still exploring the dynamics of established and proposed particles in the early universe, especially those that may drive inflation. Thus I will also describe efforts to understand different inflationary models through the lens of reheating -- particle production at the end of inflation -- and how techniques developed for this work can be applied in other arenas such as studying modified gravity. I will discuss how these ideas make contact with data from direct detection experiments and astrophysical observations, and my participation in the planned space missions STROBE-X and eXTP.
February 27, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Cosmic Surveys in the Next Decade: Mapping the Landscape of the Universe Chihway Chang, University of Chicago/KICP
Cosmology in the next decade will be driven by data. Exploiting the information one can extract from the ongoing and upcoming large surveys will give us the power to stress-test the LCDM model with unprecedented precision and open up windows for new physics. In this talk I will present some of our work in the Dark Energy Survey Collaboration and the Large Synoptics Survey Telescope Dark Energy Science Collaboration, to analyse state-of-the-art galaxy survey data as well as getting ready for the next generation of data. I will focus on topics surrounding weak lensing analyses, including cosmology from 2-point functions, generating weak lensing mass maps, and measuring the mass profiles at the outskirts of galaxy clusters.
March 13, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar Physics of Hot Gas in Galaxy Clusters on Macro and Micro Scales Irina Zhuravleva, Stanford University
Physics of Hot Gas in Galaxy Clusters on Macro and Micro Scales
X-ray observations of hot gas in galaxy clusters revealed a variety of physical processes occurring on a broad range of spatial scales. Studying the physics of these processes is important for cluster cosmology, understanding the evolution of the most massive galaxies and testing plasma kinetic theory. The advancement in observations and theory led to significant progress in the field over the past decade. However, despite the progress, many important questions remain poorly understood. What are the properties of turbulence and bulk motions of the gas? How valid is the assumption of hydrostatic equilibrium and how strong is the mass bias? How is the AGN-injected energy thermalized in the cluster cores preventing vigorous star formation? How are non-thermal electron accelerated and what is the origin of radio halos? In my talk, I will discuss recent progress that has been done to resolve these problems. In particular, I will talk about gas velocity measurements and the equation of state of gas perturbations in cluster cores. Both provide interesting insights about the physics of radio-mode AGN feedback. I will highlight recent results from the Hitomi observatory. Finally, I will discuss current efforts to directly measure the effects of magnetic fields and plasma instabilities on the hot gas as well as future perspectives in the field.
March 20, 2018 | 12:00 PM | ERC 576 | Tuesday Seminar From Exotic to Familiar: Observing Exoplanet Atmospheres in the Coming Decade Caroline Morley, Harvard University
Observations of exoplanets to date have used the Hubble and Spitzer Space Telescopes to reveal exotic exoplanet atmospheres. Substantial resources have been dedicated to characterizing the handful of planets with radii between Earth's and Neptune's -- for which we have no counterparts in the solar system -- that are accessible to current telescopes. Observations of their transmission spectra reveal a diversity of worlds, some shrouded in clouds and others with molecular features. I will discuss the types of clouds and hazes that can obscure transmission spectra, and show the effect that these thick hazes have on the thermal emission of small exoplanets. I will discuss some of my plans for new observations during the first cycle of JWST to measure the thermal emission of these planets. The new frontier of exoplanet atmosphere studies is characterizing the atmospheres of planets more familiar to Earthlings: cold gas giants and temperate Earths. I will discuss my current work to reveal the atmosphere of a cold free-floating giant planet, and my plans for detecting a host of interesting molecules in its atmosphere with JWST. Furthermore, we will soon be able to access Earth-sized, temperate worlds for the most favorable 3 systems orbiting the small stars. I will discuss the recent discoveries of Earth-sized planets around bright M dwarfs and how we might use JWST to detect their atmospheres. Last, I will explain how we might detect oxygen and other molecules in these terrestrial atmospheres in the coming years using ground-based telescopes including the GMT.
February 8, 2018 | 12:00 PM | ERC 576 | Special Seminar Debris Disks as Probes of Planetary System Evolution Meredith MacGregor, Carnegie Department of Terrestrial Magnetism
At least 20% of nearby main sequence stars are surrounded by disks of dusty material resulting from the collisional erosion of planetesimals, larger bodies similar to asteroids and comets in our own Solar System. The resulting dust can be observed via scattered light at visible to near-infrared wavelengths or thermal emission at mid-infrared to millimeter wavelengths. Since the dust-producing planetesimals are expected to persist in stable regions like belts and resonances, the locations, morphologies, and physical properties of dust in these "debris disks" provide probes of planet formation and subsequent dynamical evolution. Observations at millimeter wavelengths are especially critical to our understanding of these systems, since the large grains that dominate emission at these long wavelengths do not travel far from their origin and therefore reliably trace the underlying planetesimal distribution. I will present ongoing work that uses observations of the angularly resolved brightness distribution and the spectral dependence of the flux density to constrain both the structure and grain size distribution of nearby debris disks. In particular, I will show new ALMA observations that place constraints on the position, width, surface density gradient, and any asymmetric structure of several well-known debris disks (including Fomalhaut, HD 32297, and HD 61005). Together these results provide an exciting foundation to investigate the dynamical evolution of planetary systems through multi-wavelength observations of debris disks.
March 8, 2018 | 12:00 PM | ERC 576 | Special Seminar Measuring Dark Energy With Supernovae and Kilonovae Dan Scolnic, KICP/University of Chicago
The next decade will be the golden age of cosmology with transients. In this talk, I will present new analyses of Type Ia Supernovae that mark the most precise measurement of dark energy to date. I will go over how this analysis ties together with the analysis of the local value of the Hubble constant, for which tension persists with the inferred value from the CMB - an exciting hint at possible departures from the standard cosmological model. I will then discuss the first measurements of the Hubble constant with kilonovae and gravitational waves. I will review the large amount of overlap between the issues that must be tackled for future progress using supernovae and kilonovae to measure cosmological parameters. Finally, I will discuss the roles that surveys like LSST and WFIRST will play and how we can harness the millions of transients discovered to make generation-defining cosmological measurements.