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Colloqiua & Seminars
Colloquia & Seminars, 2014
Dwarf Galaxies: The Nexus of Dark Matter and Chemical Evolution
Evan Kirby, University of California, Irvine
The Local Group's dwarf galaxies are near enough for exquisitely detailed, resolved stellar spectroscopy and diverse enough to conduct experiments on dark matter and chemical evolution. I have collected medium-resolution spectra for thousands of stars in many dwarf galaxies in the Local Group. Innovative techniques applied to these spectra recover velocities precise to a few km/s and detailed abundances precise to 0.1 dex. Although Milky Way satellites and field dwarf galaxies are different in many ways, their velocity dispersions show that both types of galaxy pose a serious challenge to cold dark matter. Both types also obey the same mass-metallicity relation despite the large diversity of star formation histories and detailed abundance ratios.
First WIMP search results from the Large Underground Xenon experiment
Blair NV Edwards, Yale University
The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. An overview of the experiment and detection techniques will be provided followed by results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg, demonstrating the path to the world-leading sensitivity of the LUX experiment.
From Reionization to Dark Matter with the Lyman-alpha Forest
George Becker, Institute of Astronomy, University of Cambridge
Absorption lines in the spectra of distant quasars offer one of the most powerful probes of cosmic structure. The Lyman-alpha forest traces the baryons in the intergalactic medium (IGM) over several decades in scale. The properties of the baryons, in turn, reflect the ongoing interaction between luminous objects and the IGM, as well as the nature of dark matter itself. I will present recent results from a suite of projects focused on determining some of the most basic properties of the high-redshift IGM, including its temperature, ionization state, and small-scale density structure. These measurements are providing new insights into when and how the IGM was reionized, the properties of high-redshift galaxies, as well as the viability of warm dark matter. I will also discuss how upcoming IGM studies with current and next-generation facilities will advance our understanding of these and other topics.
Star Formation in a Galactic Context
Adam Leroy, National Radio Astronomy Observatory
Gas accretion from the cosmic web and its transformation into stars drives the evolution of galaxies. Consequently, the formation of molecular clouds and then stars are significant steps in our cosmic origins. Understanding these processes in a galactic context represents a major, long-standing goal of astronomy. New facilities across the spectrum, including ALMA, at last give us the tools to identify the physical drivers of these processes across the galaxy population. I will discuss our current knowledge and future prospects focusing on three key steps: the emergence of a molecular interstellar medium, the formation of dense gas within this medium, and the formation of stars from this dense gas. Each of these processes represents a limiting step across a key part of the galaxy population, from dwarf galaxies to starbursts. In particular, I will show how an interplay of metallicity and gravity drives the molecular abundance and show how dense, turbulent superclouds drive the enhanced efficiency in starbursts. Finally, I will highlight the exciting prospects for rapid progress in this field using the awesome spatial resolution and sensitivity to physical conditions of the next generation of long wavelength instruments.
To Build an Elliptical Galaxy
Jenny Greene, Princeton University
I will discuss two essential aspects of elliptical galaxy formation: how they get their stars, and how they lose their gas. For the former, I use integral-field observations of local massive galaxies to study the stellar populations and kinematics of stars at large radius, to understand the origin of the size growth of elliptical galaxies. Then I focus on black hole feedback as a means of clearing gas from massive galaxies. I show that luminous obscured quasars have ubiquitous, round ionized outflows with very high gas dispersions of nearly 1000 km/s out to 20 kpc. Finally, if time permits I will combine these two themes and present our recent search for sub-pc supermassive black hole binaries.
The chemo-dynamical structure of the Milky Way
Jo Bovy, Institute for Advanced Study
Observations of the structure and dynamics of different stellar populations in the Milky Way's disk provide a unique perspective on disk formation, evolution, and dynamics. I will review our current knowledge of the chemo-orbital structure of the disk and its implications for our understanding of how the Milky Way formed and evolved. In particular, I will show recent results from a dissection into mono-abundance populations (MAPs) of the Galactic disk based on SDSS/SEGUE data. These results show that the individual components are simple, but exhibit very different spatial and kinematic structure, with important implications for the formation and evolution of the Milky Way's disk. I will further present a new dynamical measurement of the MW's surface density between 4 and 10 kpc, obtained by rigorous 3-integral modeling of the vertical kinematics of MAPs. Combined with the latest measurements of the MW's rotation curve, this allows us to separate the disk and halo contributions to the gravitational potential and to measure the mass of the MW's stellar disk.
Direct Imaging of Extrasolar Planets
Bruce Macintosh, LLNL
With current technology, young (<100 Myr) planets can be directly imaged - resolved from their parent star - in the near-infrared with adaptive optics. I will discuss the first system of extrasolar planets to be imaged - the four planets orbiting the young F0 star HR8799. The outer two planets have been characterized spectroscopically using adaptive optics on the Keck telescope, showing non-equilibrium chemistry as well as evidence of composition enhanced in C/O from the original stellar nebula. The supply of young stars in the solar neighborhood suitable for such searches has been essentially exhausted. Providing a statistically significant sample of planets, and accessing Jupiter-like masses and separations, will require dedicated instruments. The Gemini Planet Imager is one such facility, combining advanced adaptive optics with a coronagraph and near-infrared integral field spectrosgraph. Designed to be an order of magnitude more sensitive than current instruments, GPI had first light in November 2011. I will present results here.
Assessing the Role of Stellar Feedback from Small to Large Scales
Friday noon seminar
Laura Lopez, Massachusetts Institute of Technology
Stellar feedback has a profound influence in many astrophysical phenomena, yet it is often cited as one of the biggest uncertainties in galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) where feedback occurs and the large scales (>1 kpc) of galaxies that are shaped by this feedback. In this talk, I will show how multiwavelength observations can be used to overcome these challenges and to assess the role of many stellar feedback mechanisms (e.g., radiation, photoionization, stellar winds, supernovae, protostellar outflows, and cosmic rays). I will present results from the application of this approach to a variety of sources and discuss the implications regarding the dynamics of star-forming regions. Finally, I will highlight the exciting prospects of using current and upcoming facilities to explore feedback in the diverse conditions of nearby galaxies and to probe the effect of feedback on molecular gas properties.
The role of ultra-luminous galaxies in galaxy formation and evolution
Scott Chapman, Dalhousie University (Canada)
I will provide an overview of ultra-luminous galaxies (L_IR>10^12 Lsun) at high redshift, and the different roles and properties they appear to exhibit as a function of their luminosity. I will focus on the molecular gas properties of the galaxies as the crucial fuel available for star formation, emphasizing our recent work with ALMA and the IRAM Plateau-de-Bure, where we have studied galaxies preselected at various wavelengths, and conducted blind surveys for CO gas. I will conclude with wide field surveys that are uncovering the most extreme specimens of star forming galaxies in the universe, and point to future facilities which will push the field to a new level of understanding.
Very High Energy Photons from Distant Blazars and the Potential for Cosmological Insight
Amy Furniss, Stanford University
Gamma-ray blazars are among the most extreme astrophysical sources, harboring energetic phenomena far beyond that attainable by terrestrial accelerators. These galaxies are understood to be active galactic nuclei that are powered by accretion onto supermassive black holes and have relativistic jets pointed along the Earth line of sight. The very high energy photons emitted by these extragalactic sources are detectable with ground based imaging atmospheric Cerenkov telescopes such as VERITAS. As these photons propogate extragalactic distances, the interaction with the diffuse starlight that pervades the entire Universe results in a distance and energy dependent gamma-ray opacity, offering a unique method for probing photon densities on cosmological scales. These galaxies have also been postulated to be potential sources of ultra-high-energy cosmic rays, a theory which can be examined through the deep gamma-ray observations of sources which probe moderate gamma-ray opacities.
Steve Kahn, Stanford National Accelerator Laboratory
Rest-frame Optical Spectra: A Window into Galaxy Formation at z~2
Alice Shapley, UCLA
Rest-frame optical spectroscopy provides basic insight into the stellar and gaseous contents of galaxies. Until now, our knowledge of the rest-frame optical spectroscopic properties of galaxies at 1.5<=z<=3.5 has been extremely limited, despite the critical importance of this cosmic epoch for the assembly of galaxies and the growth of black holes. The recent commissioning of the MOSFIRE spectrograph on the Keck I telescope represents a major development for the study of the rest-frame optical properties of high-redshift galaxies. The MOSFIRE Deep Evolution Field (MOSDEF) Survey fully exploits the new capabilities of MOSFIRE, charting the evolution of the rest-frame optical spectra for ~2000 galaxies in three distinct redshift intervals spanning 1.5<=z<=3.5 -- more than an order of magnitude improvement over existing surveys. With MOSDEF, we address key questions including: What are the physical processes driving star formation in individual galaxies? How do galaxies exchange gas and heavy elements with the intergalactic medium? How are stellar mass and structure assembled in galaxies (in situ star formation vs. mergers)? What is the nature of the co-evolution of black holes and stellar populations? In this talk I will present early science results from the MOSDEF survey.
Chasing the Cosmic Dawn with 21 cm Tomography
Joshua S Dillon, MIT
Realizing the promise of 21 cm cosmology to provide an exquisite probe of astrophysics and cosmology during the cosmic dark ages and the epoch of reionization has proven extremely challenging. We're looking for a small signal buried under foregrounds orders of magnitude stronger. We know that we're going to need very sensitive, and thus very large, low frequency interferometers, which present their own set of difficulties. And, as I will explain, we're going to need a rigorous statistical analysis of the maps we make to extract interesting cosmological information. I will discuss the steps we've taken to overcome these obstacles with prototype data from the Murchison Widefield Array by isolating foregrounds to a region of Fourier space outside a clean ''epoch of reionization window.'' Additionally, I will present some of most recent and exciting predictions for what 21 cm cosmology can tell us as we move to larger telescopes and higher redshifts.
Dark Energy Survey: Early Results
Brian D Nord, Fermilab
The expansion of the universe is accelerating, a discovery that earned the 2011 Nobel Prize in physics. Is cosmic acceleration due to "dark energy," or do we need to modify Einstein's General Relativity? If it is a new form of energy, is it constant or changing in time? Addressing these questions is the primary goal of the Dark Energy Survey (DES). After achieving first light in 2012, followed by months of commissioning and science verification, DES has just completed its first season of science observations at the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The DES Collaboration built a new 570-megapixel digital imager, the Dark Energy Camera (DECam), to carry out a deep, wide survey over the course of five (5) years---observing thousands of Type-Ia supernovae and hundreds of millions of galaxies. The thick, red-sensitive imager will allow us to see more supernovae and galaxies at higher redshift than previous surveys, like the Sloan Digital Sky Survey (SDSS). These observations will provide a suite of cosmological signatures: the Supernova Hubble diagram, galaxy cluster number counts, large-scale galaxy clustering and weak gravitational lensing. With this data, we will probe both the cosmic expansion history and the growth of large-scale structures, and thus explore the nature of dark energy. I will discuss the motivation for DES, the first years of operation and early results.
Axions and Moduli in Cosmology: from the Primordial Epoch to Galaxy Formation
David J. E. Marsh, Perimeter Institute
Axions and Moduli are ubiquitous in theories of beyond the standard model particle physics, in particular those containing SUSY and/or extra dimensions. The mass scales of these particles are unknown and so priors are important and can be motivated by various considerations, including naturalness, least information, or even within string theory. When masses span a large range, so do the cosmological phenomena produced. In this talk I will explore two aspects of the physics of axions and moduli with relevance to cosmology and astrophysics. Firstly, I will discuss the generation of perturbations in dark matter and dark radiation during and following inflation, and how, using CMB data, these constrain the inflationary epoch and SUSY. In the second half of the talk I will discuss late time dark matter phenomenology of axions. Ultra-light axions can behave as "Fuzzy" dark matter, and imprint a characteristic scale on structure formation. For a particular range of masses this scale is relevant to the small-scale problems of cold dark matter, and can out-perform a warm dark matter solution. I will close with discussing future prospects from data and challenges for theoretical techniques.
News from the Extreme Energy Cliff
Angela Olinto, The University of Chicago
Thanks to giant extensive air-showers observatories, such as the Pierre Auger Observatory and the Telescope Array, we now know that the sources of ultrahigh energy cosmic rays (UHECRs) are extragalactic. We also know that either they interact with the CMB as predicted or they run out of energy at the same energy scale of the CMB interactions! Their composition is either surprising (dominated by heavier nuclei at the highest energies) or the hadronic interactions at 100 TeV are not a standard extrapolation of LHC interaction energies. Hints of anisotropies begin to appear as energies reach 60 EeV, just when statistics become very limited.
Basic questions remain unanswered: What generates such extremely energetic particles that reach above 10^20 eV (100 EeV)? Where do they come from? How do they reach these energies? What are they? How do they interact on their way to Earth and with the Earth's atmosphere?
To answer these questions larger statistics at the highest energies is necessary. Space-based observatories can significantly improve the exposure to these extremely energetic particles. The first step to answer these questions is to place a wide field UV telescope at the International State Station to monitor the Earth's atmosphere from above. This is the goal of the JEM-EUSO mission: the Extreme Universe Space Observatory (EUSO) at the Japanese Experiment Module (JEM).
Cosmology with the Cosmic Microwave Background
Friday noon seminar
John Carlstrom, The University of Chicago
From its discovery 50 years ago through recent measurements of its fine angular scale anisotropy, the study of the cosmic microwave background (CMB) has led to surprises and spectacular progress in our quest to understand the origin, make up and evolution of our universe. We now have a standard cosmological model, LCDM, that fits all cosmological data with only six parameters -- although tensions in the data are beginning to surface. Far from being the last word in cosmology, the model points to exciting times ahead using the CMB to explore new physics, i.e., inflation, dark matter, dark energy, neutrino masses and possibly extra relativistic species, or dark radiation. This talk will review the current status of CMB measurements, with an emphasis on recent results from the South Pole Telescope, and discuss ongoing work and future plans for increasingly sensitive polarization and fine angular scale anisotropy measurements.
Taking the Measure of Dark Energy with DESI
Natalie Roe, LBNL
Cosmology from the Lyman-alpha Forest
Anze Slosar, Brookhaven National Laboratory
I will discuss recent results from measurements of the Lyman-alpha forest in the spectra of distant quasars by the Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS-III). Our main success to date is detection of the baryon acoustic oscillation feature at z ~ 2.4 in the three-dimensional correlation function of the transmitted flux fraction. This result is derived from a sample of ~60k quasars in Data Release 9. In a striking confirmation of the standard cosmological model, the position of the baryonic peak is measured with 2% statistical and 1% systematic error and is consistent with the LCDM model. Pending permission from the collaboration, I will present results for the ~140k high redshift quasars in the Data Release 11. In addition and somewhat unexpectedly, we have also detected BAO in the cross-correlation between Lyman-alpha forest and quasar positions. Combination of low and high-redshift BAO measurements allow us to put non-trivial constraints on the cosmological model without inclusion of the CMB data. Finally, I will mention some of the other developments: measurement of the 1D power spectrum of flux fluctuations, first measurements of the Lyman-beta forest power spectrum and renewed efforts to simulate the intergalactic medium responsible for the forest.
Exciting results from BICEP2
Clem Pryke, Chris Sheehy and Abigail Vieregg
A Tale of Two Collaborations: A New Precise Measurement of Cosmological Parameters Using Type Ia Supernovae
Rick Kessler, The University of Chicago
Excess of Diffuse Gamma-ray Emission from the Inner Galaxy: Bubbles, Jets, and Dark Matter
Meng Su, MIT
Our analysis of data from the Fermi Gamma-ray Space Telescope revealed a pair of large gamma-ray bubble structures, named the Fermi bubbles, each extending ~10 kpc above and below the Galactic center. I will present new results using five years Fermi-LAT data and multi-wavelength observations of the Fermi bubbles in X-ray, microwave, and radio, including updates from dedicated observations. New observations help us to distinguish hadronic from leptonic origin of the cosmic-ray electrons emitting gamma-ray/radio emission, and constrain the magnetic field within the Fermi bubbles. I will also show our numerical simulations which demonstrate that the bubble structure could be evidence for past accretion events and outflow from the central supermassive black hole. Furthermore, we recently found gamma-ray evidence for large-scale collimated jet-like structure penetrating through the bubbles from the Galactic center, which might provide further evidence of a past activity in the Galactic center. We have proposed to change the survey strategy of Fermi to increase the exposure at the inner Galaxy by more than a factor of 2. This new survey strategy has been initiated since December 2013 and will last for at least one year. I will end up with a discussion of future gamma-ray space missions.
The GMT Project: Science and Status
Rebecca Bernstein, Carnegie Observatories
In this talk, I will give an overview of the GMT project and the science cases and goals that are driving its design. I will also describe the current status of the project and the first generation instruments that are now under development.
Science with CMB Spectral Distortions: a New Window to Early-Universe Physics
Jens Chluba, JHU
Since COBE/FIRAS we know that the CMB spectrum is extremely close to a perfect blackbody. There are, however, a number of processes in the early Universe that should create spectral distortions at a level that is within reach of present day technology. I will give an overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open up an unexplored window to early-universe and particle physics, with possible non-standard surprises but also guaranteed signals awaiting us.
Measuring the Power Spectrum of Dark Matter Substructure with Gravitational Lensing
Yashar Hezaveh, Stanford University
The abundance of substructure within dark matter halos surrounding galaxies has been an area of intensive study for over a decade.
Quantifying the small-scale structure of dark matter halos, which is influenced by the spectrum of primordial density fluctuations and the micro-physics of dark matter, can allow us to probe multiple areas of fundamental physics. Observationally, however, very little is known about the true abundance and the structure of dark matter sub-halos.
In this talk, I will discuss the promising prospects of using ALMA and the recently discovered populations of strong gravitational lenses in mm/submm-wave surveys (SPT, Herschel, ACT, Planck) for mapping the small-scale structure of galaxy halos. In particular, I will show that we can measure the power spectrum of dark matter substructure by analyzing the correlations in perturbations of strongly lensed images.
I will show that the large number of discovered lenses and the spectacular power of ALMA paint a bright future for a robust characterization of the small-scale structure of dark matter halos.
Asteroseismology and Exoplanets: A Kepler Success Story
Daniel Huber, NASA
Asteroseismology - the study of stellar oscillations - is a powerful observational tool to probe the structure and evolution of stars. In addition to the large number of newly discovered exoplanets, the Kepler space telescope has revolutionized asteroseismology by detecting oscillations in thousands of stars from the main-sequence to the red-giant branch. In this talk I will highlight recent asteroseismic discoveries by Kepler, focusing in particular on studies of exoplanet host stars and the application of asteroseismology to measure stellar spin-orbit inclinations. I will furthermore discuss current efforts to improve fundamental properties (such as temperatures, masses, and radii) of Kepler targets, and their importance for deriving accurate planet occurrence rates using the Kepler sample. Finally, I will give a brief overview on first results by Kepler's ecliptic plane follow-up mission, K2.
Searches for Particle Dark Matter
Tim M.P. Tait, UC Irvine
Dark Matter is all around us, a clear sign of physics beyond the Standard Model, and yet we will have not understood what it is and how it fits into the larger picture. In this talk, I will discuss what we know about dark matter and how different kinds of searches, including searches for its collision with heavy nuclei, production at accelerators, and signs of its annihilation in our galaxy, combine together to give us information about how it (doesn't) interact with ordinary matter. The picture that will emerge is one where different searches complement each other, offering rich opportunities to understand the nature of dark matter in the near future.
The Weak Lensing Signal and Clustering of SDSS-III CMASS Galaxies
Hironao Miyatake, Princeton University
Weak gravitational lensing is a powerful tool to understand how galaxies populate dark matter halos. In this talk, I report a weak lensing measurement of SDSS-III/CMASS galaxies, which is a luminous, high redshift (z~0.5), spectroscopic galaxy sample. For this analysis, I use the publicly-available CFHTLenS galaxy catalog for shapes and photometric redshifts of source galaxies. After performing systematic tests carefully, I find a highly significant detection of the CMASS weak lensing signal with signal-to-noise ratio of 28. Combining with clustering signals, I fit a halo model to the measurements. Based on this result, I will discuss details of matter properties of the CMASS galaxies such as stellar mass and halo concentration. In addition, I will introduce preliminary results of cosmological constraints obtained by combining the lensing and clustering measurements.
Turbulence and dynamo action in accretion flows
Fausto Cattaneo, University of Chicago
The most remarkable thing about accretion discs is that they accrete. The rate at which material can be accreted from a disc onto a central compact object is controlled by the rate at which angular momentum can be transported out of the disc. Thus efficient accretion requires efficient angular momentum transport, typically many orders of magnitude larger than what could be accounted by viscous processes alone. Consequently, it has long been assumed that astrophysical discs must be turbulent, and that the turbulence is what causes the enhanced transport. Yet, basic considerations indicate that discs with near-Keplerian velocity profiles should be hydrodynamically stable. Thus the accretion disc conundrum: how can a stable system be turbulent?
One possible resolution is that, in an electrically conducting disc, the presence of a weak magnetic field drastically alters the stability property of the disc. A powerful, rapidly growing instability—the magneto-rotational-instability (MRI), can develop, lead to turbulence and efficiently transport angular momentum outwards. Better still, there is evidence that turbulence driven by the MRI can, through dynamo action, regenerate the very magnetic field necessary for the instability to develop in the first place.
In this talk I shall introduce the basic physics underpinning the MRI, present some numerical models of MRI-driven turbulence and show how it can lead to the self-driven magnetization of a disc.
The first three years of AMS-02 experiment on the International Space Station
Veronica Bindi, University of Hawaii
The Alpha Magnetic Spectrometer (AMS-02) is a precision large-acceptance high energy particle detector which was successfully deployed in 2011 on the International Space Station (ISS) where it will operate for the next decades. To date, the detector has collected over 40-billion cosmic ray events. Among the physics objectives of AMS are a search for the understanding of Dark Matter, Antimatter, the origin of cosmic rays and the exploration of new physics phenomena. An overview of the operations and performance of the AMS-02 detector as well as the results based on data collected during the first three years of operations in space will be presented.
The GeV Excess in the Inner Galaxy: Pulsars or Dark Matter?
Douglas P Finkbeiner, Harvard University
Seeking Gravity and Light from Binary Supermassive Black Holes
Sarah Burke Spolaor, California Institute of Technology
In a major merger, two supermassive black holes will meet at the center of the merger remnant. Before their eventual coalescence, the giant black hole pair endures prolonged interaction with its environment, which may produce electromagnetic emissions. If observed, these would represent direct probes of late-stage merger dynamics, and could provide a smoking gun for gravitational wave emitters detectable by "Pulsar Timing Arrays".
No small-orbit binary systems have yet been conclusively confirmed. We are investigating the use of both electromagnetic observations and Pulsar Timing Arrays to constrain, support, or disprove the binary SMBH hypothesis in current candidate binary systems. We will present results from ongoing searches for binary supermassive black holes, and will consider the prospects of Pulsar Timing Arrays to place physically interesting gravitational wave limits on target systems.
Lessons from two success stories
Gabriele Veneziano, College de France
Our present understanding of Nature is based on the Concordance Model of gravity and cosmology and on the Standard Model for the constituents of matter and their non-gravitational interactions. Their amazing successes --and puzzles-- may carry some important lessons for our quest of a truly unified theory of space, time, and matter.
Towards a first measurement of pp neutrinos in real time
Pablo Mosteiro, Princeton University
The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. Neutrinos produced by these nuclear reactions exit the Sun and reach Earth within minutes, providing us with key information about what goes on at the core of our star. This talk presents progress towards the rst measurement of pp neutrinos in the Borexino detector, which would be the rst direct real-time measurement of pp neutrinos independent of other experiments. This would be, furthermore, another validation of the LMA-MSW model of neutrino oscillations. In addition, it would complete the spectroscopy of pp chain neutrinos in Borexino, thus validating the experiment itself and its previous results.
The Dynamic Universe: Palomar Transient Factory
Shri Kulkarni, California Institute of Technology
That occasionally new sources ("Stella Nova") would pop up in the heavens was noted more than a thousand years ago. The earnest study of cosmic explosions began in earnests less than a hundred years ago. Over time, astronomers have come to appreciate the central role of supernovae in synthesizing new elements (and making life as we know possible).
The Palomar Transient Factory (PTF), an innovative 2-telescope system, was designed to explicitly chart the transient sky with a particular focus on events which lie in the nova-supernova gap. PTF can find an extragalactic transient every 20 minutes and a galactic (strong) variable every 10 minutes. The results so far: classification of 2000 supernovae; identification of an emerging class of ultra-luminous supernovae; the earliest discovery of a la supernovae; discovery of luminous red novae; the most comprehensive UV spectroscopy of la supernovae; discovery of low energy budget supernovae; clarification of sub-classes of core collapse and thermo-nuclear explosions; mapping of the systematics of core collapse supernovae; identification of a trove of eclipsing binaries and the curious AM CVns.
Supernova neutrinos at present and future underground detectors
Cecilia Lunardini, Arizona State University
A core collapse supernova is a very powerful source of ~ 10-20 MeV neutrinos. In the extreme environment of the collapsing star, the phenomenology of these neutrinos is very rich, and, in many respects, unique. I will first review the theory of neutrino emission and propagation inside a supernova, with focus on the physics of neutrino oscillations. In the second part of the talk, I will discuss what fundamental properties might be learned from future detections of supernova neutrinos. I will emphasize the potential of studying the diffuse flux of neutrinos from all the supernovae in the universe. This flux is constant in time and therefore it is a guaranteed signal at a detector of mass 0.1 Mt or higher. It also offers a unique possibility to study the whole population of supernovae, including those with failed or very dim explosions.
From Hot Jupiters to Habitable Worlds: A Survey of Exoplanet Atmospheres
Heather Knutson, California Institute of Technology
Although the space-based Kepler survey has dominated discussions of exoplanet statistics in recent years, ground-based surveys have been undergoing a quiet renaissance of their own. This has resulted in an ever-growing sample of lower-mass and longer-period planets transiting bright, nearby stars. Such systems provide a unique opportunity to extend the current statistical studies of hot Jupiter atmospheres down to smaller and cooler planets (so-called "super-Earths") that are still favorable for detailed characterization. The best-studied planets in this regime have puzzling properties that have yet to be adequately explained; in my talk I will present new measurements from Hubble and Spitzer that aim to place these planets in a larger statistical context and to illuminate their formation and migration histories. These studies also serve to illustrate the crucial role of space-based infrared telescopes (both present and future) in addressing some of the most exciting and pressing questions related to low-mass exoplanets.
Planck Data Reconsidered
Renee Hlozek, Princeton University
We re-analyse the Planck data and find that the 217GHz x 217GHz detector set spectrum used in the Planck analysis is responsible for some of the tension between the Planck parameters and other astronomical measurements. We will describe our map-based foreground cleaning procedure, which relies on a combination of 353 GHz and 545 GHz maps to reduce residual foregrounds in the intermediate frequency maps used for cosmological inference. While in broad agreement with the results reported by the Planck team, the parameters we obtain using our foreground cleaning imply a universe with a lower matter density of Omega_m=0.302 +- 0.015, and parameter values generally more consistent with pre-Planck CMB analyses and astronomical observations. We compare our cleaning procedure with the foreground modelling used by the Planck team and find good agreement. The difference in parameters between our analysis and that of the Planck team is mostly due to our use of cross-spectra from the publicly available survey maps instead of their use of the detector set cross-spectra which include pixels only observed in one of the surveys. We show evidence suggesting residual systematics in the detector set spectra used in the Planck likelihood code, which is substantially reduced for our spectra.
Gravitational wave astrophysics with LIGO
Daniel Holz, University of Chicago
Gravitational waves were first predicted by Einstein almost a century ago, and the Laser Interferometer Gravitational wave Observatory (LIGO) should be finally on the verge of directly detecting these waves. The most likely sources are the inspirals and mergers of stellar mass binary systems, such as pairs of neutron stars and/or black holes. In addition to being extraordinarily loud in gravitational waves, these coalescences may be associated with short gamma-ray bursts, and thus hold out the promise of multi-messenger astronomy: combining gravitational wave and electromagnetic observations to elucidate the physics and astrophysics of the sources. We present estimates for the event rate of binary systems, showing that LIGO can expect the first detections within months of operation. We examine the sky localization of LIGO sources, and explore some of the results that can be expected from gravitational wave astronomy, including shedding light on the process of black hole formation and precision measurements of the Hubble constant. We also discuss the loudest gravitational wave sources, and the potential to use these for internal calibration as well as for science. The era of gravitational-wave astronomy is rapidly approaching; a revolutionary new probe of our Universe awaits.
Weighing the Giants: Accurate Weak Lensing Mass Measurements for Cosmological Cluster Surveys
Friday noon seminar
Anja von der Linden, DARK + KIPAC
Surveys of galaxy clusters provide a sensitive probe of cosmology by measuring the evolution of the halo mass function. With a number of surveys at optical, millimeter, and X-ray wavelengths on-going or starting in the near futures, cluster count experiments will be one the most important cosmological probes over the next decade. However, none of the typical survey observables (X-ray luminosity, optical richness, SZ flux) directly measures the cluster mass. Already current cluster surveys are systematically limited by uncertainties in the relation between cluster mass and observables. Cluster weak lensing is the most promising observational method to calibrate the mass scaling to the required precision, but requires the control of systematic errors to a few percent each. I will review our "Weighing the Giants" project to measure accurate individual weak lensing masses for the largest sample of clusters to date, and discuss its first cosmological applications for cluster count experiments as well as the baryonic mass fraction test.
Exoplanets in HD
Jacob Bean, University of Chicago
Exoplanet surveys have revealed an amazing diversity of planets orbiting other stars in the last two decades. Studying the atmospheres of representative exoplanets is the key next step in leveraging these detections to further transform our understanding of planet formation and planetary physics. Additionally, atmospheric studies are critical for determining if any of the small habitable zone exoplanets that are now being detected are truly habitable, and even inhabited. In this talk I will describe a vision for how we can pursue the compelling opportunities in exoplanet atmospheres today and in the future. One crucial need in this area is spectroscopy to reveal planets in high definition. I will present new results from intensive observational campaigns with the Hubble Space Telescope that serve as a model for the proposed program, including a definitive constraint on the atmosphere of the super-Earth archetype GJ1214b, a precise measurement of the water abundance in a giant planet, and the inference of the thermal structure of an exoplanet atmosphere as a function of longitude. A fundamental component of the envisioned approach for the future is the need for a strategic program combining observations with multiple ground- and space-based telescopes using a suite of techniques to investigate the question of habitability. I will conclude by discussing how future facilities like the Giant Magellan Telescope are poised to play a crucial role in the identification of the first Earth twin as part of this plan.
Effective field theories for cosmic acceleration
Raquel H Ribeiro, Case Western Reserve University
In this era of precision cosmology we are relying more than ever on our theories to decode observations. Models phrased in an Effective Field Theory (EFT) language are particularly useful, since they rely on the existence of a decoupling limit which makes the low energy physics phenomena largely independent of short distance physics. Why is such description desirable? It means we don't need to know the full behaviour of the theory, but only its low energy limit to make predictions for observables at the scale of the experiment we are interested in.
In this talk I will discuss a different reorganisation of EFTs describing single-field models for cosmic acceleration (in the early and late universe) with large derivative interactions. The decoupling limit in these theories relies on a derivative hierarchy, rather than a hierarchy between energy scales. Examples include Dirac--Born--Infeld inflation and galileon models in the context of modified gravity. I will discuss the criterion of predictivity of these theories and identify the scales up to which the predictions of these theories are reliable to decode observational data.
Cosmological Imprints of Dark Matter Produced During Inflation
Daniel Chung, University of Wisconsin, Madison
Dark matter produced during inflation can naturally leave observable isocurvature imprints in the inhomogeneities of our universe. I survey the progress in theoretically cataloging such imprints, along with their connections with high energy theory and observations.
Bridging the gap between cosmology and star formation: Feedback on galactic and cosmological scales
Claude-Andre Faucher-Giguere, Northwestern University
Star formation is observed to be very inefficient, both within galaxies and cosmologically. Feedback from massive stars and growing black holes has emerged as the most promising solution to explain these facts and broadly bring galaxy formation models in agreement with observations. However, most galaxy formation models to date have had to rely on significant simplifying assumptions and parameters must typically be tuned to obtain realistic galaxy populations. I will argue that the predictive power of cosmological simulations of galaxy formation can now be greatly improved by directly resolving the main structures in the interstellar medium of galaxies and bridging the historical gap between cosmological models and detailed studies of star formation and feedback on galactic scales. I will present new high-resolution simulations of supernova remnant evolution in an inhomogeneous medium and show how the results can be used to model supernova feedback more accurately in cosmological simulations. I will then introduce the FIRE ("Feedback In Realistic Environments") cosmological simulation project and present early results on the predicted stellar mass function of galaxies, galactic winds, and properties of halo gas around high-redshift galaxies.
Two milestones in the history of the Universe: last scattering surface and black body photosphere of the Universe
Rashid Sunyaev, Max-Planck Institute for Astrophysics
Reception at 4 PM in the LASR conference room.
Exploiting the non-linear regime of galaxy clustering in SDSS-III BOSS
Beth A Reid, UC Berkeley
The size of both galaxy redshift surveys and N-body simulations of dark matter clustering have grown tremendously over the past few decades, which provides the opportunity to exploit the quasi- and non-linear regime for cosmological information. I will discuss the observational and theoretical challenges in measuring and modeling the small-scale redshift space clustering of galaxies in SDSS-III BOSS, as well as its great promise -- we infer the growth rate of cosmic structure at z=0.57 to 2.5% precision and robustly predict the impact of "galaxy" physics on clustering in the quasi-linear regime. I will demonstrate quantitatively the importance of precise models for broadband clustering in the quasi-linear regime for future redshift survey constraints on dark energy and neutrino mass.
Merging Compact Binaries
Dong Lai, Cornell University
The merger of binary systems containing neutron stars, black holes or white dwarfs can lead to various extreme phenomena that are observable throughout the universe. I will discuss recent works on merging neutron star/black hole binaries and white dwarf binaries, focusing on dynamical processes in the pre-merger phase, gravitational waves, tidal and electromagnetic interactions, and potential constraint on dense nuclear matter.
The Curious Case of the 3.57 keV Emission Line
Esra Bulbul, Harvard-Smithsonian Center for Astrophysics
We recently detected an unidentified emission line at 3.57 keV in the Chandra observations of the Perseus cluster and the stacked XMM-Newton observations of 73 galaxy clusters. This line was detected at >3sigma statistical significance in five independent samples of XMM-Newton. The lack of any atomic transitions at this energy in thermal plasma, hints that the line could be a signature of decaying sterile neutrinos. I will discuss the search for this line in the stacked observations of galaxy clusters and provide an update on active searches for this feature in other dark matter rich astrophysical systems.
Science Highlights from the Nuclear Spectroscopic Telescope Array (NuSTAR): Bringing the High Energy Universe into Focus
Fiona Harrison, California Institute of Technology
The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray (3 - 79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate. With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants. I will describe the mission and present recent science highlights.
Directional Detection of the Cosmic Neutrino Background
Benjamin R. Safdi, MIT
The cosmic neutrino background (CvB), produced about one second after the Big Bang, permeates the Universe today. New technological advancements make neutrino capture on tritium a promising path forward towards the detection of the CvB. I will show that gravitational focusing by the Sun causes the expected neutrino capture rate to modulate annually. The amplitude and phase of the modulation depend on the phase-space distribution of the local neutrino background, which is perturbed by structure formation. Gravitational focusing is the only source of modulation for neutrino capture experiments, in contrast to dark-matter direct-detection searches where the Earth's time-dependent velocity relative to the Sun also plays a role. I will also show that CvB observatories may measure anisotropies in the cosmic neutrino velocity and spin distributions by polarizing the tritium targets. The polarized-target measurements may constrain non-standard neutrino interactions, such as neutrino magnetic dipole moment interactions, that would induce larger anisotropies and help discriminate between Majorana versus Dirac neutrinos.
The Fermi Gamma-Ray Space Telescope: An Update
Peter F Michelson, Department of Physics, Stanford University
The Fermi Gamma-Ray Space Telescope was launched in 2008. After 6 years in orbit, Fermi continues to bring new insights into the sources of high-energy radiation in the Galaxy and beyond. In this talk, I will describe upgrades to the science performance of Fermi (aka Pass 8) and highlights of recent discoveries.
The Fermi bubbles
Anna Franckowiak, SLAC / KIPAC
The Fermi bubbles are two large structures in the gamma-ray sky extending up to 55 deg above and below the Galactic center. I will present the analysis of 50 months of Fermi-LAT data from 100 MeV to 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. I will show results on the spectral shape, spatial substructure, variability of the spectrum as a function of latitude and an estimate of the width of the bubble boundary. I will discuss the modeling of the gamma-ray spectrum with hadronic and leptonic models and the possible relation to the microwave haze.
Luminous neutron stars
Andrei Beloborodov, Columbia University
Neutron stars were discovered as radio pulsars in 1967. At a glance, pulsars are merely fast-rotating magnetized spheres. They are observed to generate powerful beams of coherent radio waves and huge luminosity in gamma-rays; their emission mechanism has remained a puzzle for four decades. Today, this puzzle can be fully resolved using first-principle numerical experiments. I will describe such an experiment and its first results.Then I will discuss the most fascinating class of neutron stars -- magnetars, whose activity is fed by the dissipation of magnetic energy. I will describe the mechanism of X-ray emission from magnetars, their giant gamma-ray flares, and the behavior of the solid crust broken by magnetic stresses. Finally, I will describe the NuSTAR discovery of a new class of ultra-luminous accreting neutron stars and discuss the implications of this discovery.
Conformal Fermi coordinates and the local universe formalism
Friday noon seminar
Liang Dai, Johns Hopkins University
In an inhomogeneous Universe, the physical effect of long-wavelength perturbation on short distances should be such that short-wavelength perturbations effectively evolve in a modified homogeneous universe. We explicitly construct the so-called conformal Fermi normal coordinates (CFNC) through an expansion around the observer's geodesic, which describe the local spacetime as a quasi-FRW metric and are valid at all times. The CFNC formalism demonstrates that the zeroth-order picture is that local expansion rate and spatial curvature are renormalized by long-wavelength perturbations, and the general condition for the spatial curvature to be a constant is derived. Beyond this "separate universe" picture, CFNC allows for systematic survey of additional local effects from long-wavelength perturbations that cannot be attributed to a re-definition of the background FRW cosmology. The formalism can be useful in the studies of tracer bias, intrinsic alignment and gravitational-wave "fossil" effect.
From Plasma Microphysics to Global Dynamics in Clusters of Galaxies, Hot Accretion Flows, and the Solar Wind
Matthew Kunz, Princeton University
Many astrophysical systems are magnetized and weakly collisional. As such, their mean, global properties are vastly separated in both space and time from the detailed kinetic microphysics that governs the transport of momentum, heat, and magnetic fields. Elucidating this physics is a vital step towards understanding why the intracluster medium avoids catastrophic cooling, how angular momentum is transported in hot accretion flows, and what shapes the observed distribution function in the solar wind. In this talk, I will present a unified description of these systems in terms of the pressure anisotropy, a directional bias in thermal pressure caused by adiabatic evolution in a magnetized plasma. Its impact on both micro- and macro-scales is examined using analytical theory and numerical simulations, the latter made possible by a new hybrid-kinetic particle-in-cell code, Pegasus (Kunz et al. 2014, JCoP, 259, 154). Pioneering studies of kinetic solar-wind turbulence, collisionless magnetorotational instability, and of fast-growing Larmor-scale instabilities will be placed within the larger context of formulating a pragmatic framework for modeling astrophysical multiscale plasma dynamics.
Do WIMPs Rule? The LUX & LZ Experiments and the Search for Cosmic Dark Matter
Daniel Akerib, SLAC
Dark Matter remains a profound mystery at the intersection of particle physics, astrophysics, and cosmology. One of the leading candidates, the Weakly Interacting Massive Particle, or WIMP, may be detectable using terrestrial particle detectors. Recent technological advances are enabling very rapid increases in sensitivity in the search for these particles. I will talk about the LUX experiment, a liquid xenon time projection chamber, which currently holds the best upper limit over much of the mass range. I will also discuss plans for a larger follow up experiment, LZ, which will just begin to measure a background neutrino signal that will set a fundamental limit our ability to search for WIMP dark matter.
Results from Planck 2014
Brendan Crill, Jet Propulsion Laboratory
Planck is the third-generation space mission aimed at measuring the Cosmic Microwave Background, a relic of the hot big bang. Launched in May 2009 Planck has surveyed the full sky in intensity and polarization with a broad range of frequencies from 30 to 857 Ghz at a resolution as fine as 5 arcminutes above 143Ghz. This month, the Planck collaboration is releasing science results and data from polarization maps of the sky from 30 to 353 GHz. In this talk, I will present the new polarized sky maps from Planck and give an overview of their impact on our understanding of the standard Lambda-CDM cosmological model. I will also discuss what Planck's data can tell us about Galactic polarized foreground emission that potentially impacts current and future searches for the imprint of inflationary gravitational waves on B-mode polarization.