April 3, 2013 | 3:00 PM | BSLC 115 | Wednesday colloquium Towards 1% measurements of cosmological distances with cosmic sound Nikhil Padmanabhan, Yale University
Measuring the accelerated expansion of the Universe with the goal of better understanding its underlying physics is one of the leading programs in cosmology today. The baryon acoustic oscillation technique is one of the foremost tools in our toolbox today. This talk will explain the underlying physics of this method and the reasons it is extremely robust to observational and theoretical systematic errors. I will then present the latest results from the SDSS and BOSS surveys, currently the most precise distance constraints from this method. These will include a new analysis technique to undo the effects of the nonlinear evolution of the density field and partially ''reconstruct'' the initial density field, and can reduce the distance errors by a factor of 1.7. I will discuss the implications of these measurements, and will conclude by discussing prospects for improvements in the immediate and not-so-immediate future.
April 10, 2013 | 3:00 PM | BSLC 115 | Wednesday colloquium Effective Field Theories for Fluids and Superfluids Alberto Nicolis, Columbia University
I will present a novel field theoretical framework that captures the long-distance and low frequency dynamics of hydrodynamical systems. The approach is that of effective field theories, whose building blocks are the long-distance degrees of freedom and symmetries. Possible applications include questions in condensed matter physics, heavy-ion collisions, astrophysics, cosmology, and quantum hydrodynamics. Finally, this formulation naturally invites (and answers) new questions in classical hydrodynamics.
April 24, 2013 | 3:00 PM | BSLC 115 | Astronomy Colloquium High redshift starburst galaxies revealed by SPT, ALMA, and gravitational lensing Joaquin D. Vieira, California Institute of Technology
The South Pole Telescope (SPT) has systematically identified a large number of high-redshift strongly gravitationally lensed starburst galaxies in a 2500 square degree cosmological survey of the millimeter (mm) sky. These sources are selected by their extreme mm flux, which is largely independent of redshift and lensing configuration. The flux magnification provided by the gravitational lensing enabled us to perform a spectroscopic redshift survey with the recently commissioned Atacama Large Millimeter Array (ALMA). We targeted 26 SPT sources and obtained redshifts via molecular carbon monoxide (CO) lines. We determine that roughly 40% of these sources lie at z>4, indicating the fraction of dusty starburst galaxies at high-redshift is far higher than previously thought. Two sources are at z=5.7, placing them among the highest redshift starbursts known, and demonstrating that large reservoirs of molecular gas and dust can be present in massive galaxies near the end of the epoch of cosmic reionization. These sources were additionally targeted with high resolution imaging with ALMA, unambiguously demonstrating them to be strongly gravitationally lensed by foreground structure. We are undertaking a comprehensive and systematic followup campaign to use these "cosmic magnifying glasses" to study the infrared background in unprecedented detail, inform the condition of the interstellar medium in starburst galaxies at high redshift, and place limits on dark matter substructure. I will discuss the scientific context and potential for these strongly lensed starburst galaxies, give an overview of our team's extensive followup efforts, and describe our latest science results.
May 1, 2013 | 3:00 PM | BSLC 115 | Wednesday colloquium Dark Matter at Colliders Shufang Su, University of Arizona
While 27% of the Universe is made of dark matter, the particle identity of the dark matter still remains a mystery. Collider studies offers a complementary tool to explore the nature of the dark matter, in addition to dark matter direct and indirect detections. In this talk, I will discuss the collider studies of the dark matter, focusing on how to observe dark matter signals, and how to distinguish dark matter scenarios. In the first part of the talk I will discuss the model-independent approach for the monojet/monophoton plus missing ET signals, as well as model-dependent signatures of dark matter produced in the cascade decay chain of parent particles. The second part of the talk will focus on the study of distinguishing multiple component dark matter with traditional single particle dark matter.
May 8, 2013 | 3:00 PM | KPTC 106 | Astronomy Colloquium Infalling groups and galaxy evolution in the IMACS Cluster Building Survey Alan Dressler, Carnegie Institution of Washington Observatories
From a photometric/spectroscopic study of galaxy clusters at z~0.4, using the wide field of the IMACS instrument on the Magellan-Baade telescope, we have studied infalling galaxies that were building typical rich clusters 4 billion years ago, and compared them to field galaxies at that epoch over the full range of galaxy environment. The results emphasize the important role of infalling groups of galaxies in building a cluster, and provide evidence that significant quenching of starforming galaxies occurs in such groups --- in both the cluster and field environment. Our study also suggests a new interpretation of the role that starbursts play in galaxy evolution.
May 15, 2013 | 3:00 PM | KPTC 106 | Astronomy Colloquium Status and Future of the APOGEE Project Steven R. Majewski, University of Virginia
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) in Sloan Digital Sky Survey III (SDSS-III) is a large-scale, near-infrared, high-resolution (R ≥ 22,500) spectroscopic survey of the Milky Way (MW) using a 300-fiber, cryogenic spectrograph operating over 1.51-1.70 µm (i.e., a large fraction of the H-band). Because of the lower H band dust extinction compared to that at optical wavelengths (AH / AV = 0.16), APOGEE effectively pierces through dust obscuration and will provide a vast, uniform database of chemical abundances and radial velocities for stars across all Galactic populations (bulge, thin and thick disks, halo). APOGEE started observations in May 2011 and in 3 years of SDSS-III bright time intends to observe of order 100,000 giant star candidates selected from the Two Micron All-Sky Survey (2MASS) across hundreds of sight lines with field limits ranging over H=11-13.5. With its high resolution and S/N (>100 per Nyquist-limit-sized pixel), APOGEE will determine precision radial velocities (presently at 100 m/s absolute accuracy and 30 m/s relative precision) and accurate abundances for numerous chemical species, including C, N, O and Fe, as well as other α, odd-Z, and iron-peak elements for its primary targets. About 5% of the APOGEE targeting is dedicated to a number of ancillary science programs that are already yielding interesting results. To date the APOGEE survey has collected more than 350,000 spectra of over 65,000 distinct stars. I will give an overview of APOGEE and some of its initial findings, and lay out our plans to expand the APOGEE survey for another 6 years and in both the Northern and Southern Hemispheres in SDSS-IV.
May 22, 2013 | 3:00 PM | BSLC 115 | Astronomy Colloquium Making Hay with ALFALFA John Salzer, Indiana University
The recently completed ALFALFA blind HI survey has produced an unprecedented catalogue of 21-cm detected objects in the local universe out to z = 0.06. With a sensitivity more than an order of magnitude better than previous wide-field blind HI surveys, ALFALFA represents the current state-of-the-art in neutral hydrogen searches. In this talk I will give a brief overview of the ALFALFA survey, then will describe two optical follow-up projects led by our group at Indiana. The first is a large narrow-band H-alpha imaging study of a volume-limited sample of ALFALFA sources. The second is a deep imaging study of nearby HI clouds that have the characteristics of being low-mass dark matter halos. One of the objects uncovered in this latter study is a nearby dwarf galaxy with fairly unique properties that we dubbed Leo P.
May 29, 2013 | 3:00 PM | KPTC 106 | Wednesday colloquium Observation of High Energy Neutrinos at IceCube Nathan Whitehorn, University of Wisconsin - Madison
Cosmic rays above the ankle (10^18 eV) are the universe's most energetic particles and must be produced in the universe's most energetic objects -- but which ones? and how? Neutrinos should be produced in whatever the cosmic accelerators are and should provide unique insights into their production mechanisms. Recent searches for high-energy (> 100 TeV) neutrinos at the antarctic IceCube neutrino observatory have produced the first evidence for a neutrino population beyond what is readily explained by neutrino production in the Earth's atmosphere from cosmic ray interactions, including the observation of several events with energies above 1 PeV -- the highest energy neutrinos ever observed. This talk will discuss the current status of these astrophysical neutrino searches in IceCube and prospects for the future.
March 29, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Symmetries of primordial perturbations Austin Joyce, University of Pennsylvania
Image credit: Planck collaboration
We will explore the symmetries underlying the statistics of the primordial perturbations which seeded the temperature anisotropies of the Cosmic Microwave Background. I will show how symmetry considerations lead us to three broad classes of theories to explain these perturbations: single-field inflation, multi-field inflation, and the conformal mechanism. We will discuss the symmetries in each case and derive their model-independent consequences.
April 5, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Exploring the properties of galaxy clusters with hydrodynamical simulations: the MUSIC dataset Federico Sembolini, Universidad Autonoma de Madrid (Spain)
I will introduce the MUSIC dataset (Marenostrum-MUltiDark Simultations of galaxy Clusters) - presently the largest sample of hydrodynamically simulated galaxy clusters, comprised of more than 700 clusters and 2000 groups. The objects have been selected from two large N-body simulations and have been resimulated at high resolution using Smoothed Particle Hydrodynamics (SPH) together with relevant physical processes that include; cooling, UV photoionization, star formation and different feedback processes associated with Supernovae explosions. The analysis of the baryon content (gas and stars) of the most massive clusters of the MUSIC dataset, performed as a function of aperture radius and redshift, is compared with the most recent observational estimates of the gas fraction in galaxy clusters, showing a good agreement when the effects of cooling and stellar feedbacks are included. A clear dependence of the gas fraction with the total cluster mass is also evident. I will present a detailed analysis of the scaling relations of the thermal SZ (Sunyaev-Zel'dovich) effect derived from MUSIC clusters. The integrated SZ brightness, Y, is one of the best observational proxies used to infer the total cluster mass, M, as SZ observations allow exploration of regions of clusters not reachable by present X-ray experiments. The analysis of the SZ scaling relations confirm the validity of the self-similar model with a very low scatter and shows a good agreement with the latest observational results, such as Planck. Furthermore, I will explore the presence of a possible redshift dependence on the Y-M scaling relation. In this scope, I extend the analysis to protoclusters, objects typically at redshift higher than 1. Under the assumption of defining a protocluster only as the largest progenitor present at a specific redshift, we are able to estimate the spherical thermal component of SZE, integrated inside the virial radius, and similarly the total mass. The analysis of the scaling relations of MUSIC clusters is completed by estimating the X-ray properties of the objects using PHOX. The X-band is considered to be the observational counterpart of the SZ effect. Beside the standard X-ray scaling relations, like the Lx-M and the T-M relations, a comparison between the X-rays and SZ properties of MUSIC clusters (focusing on scaling relations like the YX-Y and the Y-T relations) will be performed, in order to explore the relationship between galaxy cluster's properties with different observational approaches. Finally, I will use large N-body simulations, such as MultiDark and Big MultiDark, to check the evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel'dovich (kSZ) effect measured by ACT (Atacama Cosmology Telescope). Taking advantage of the extensive statistics provided by such large simulations, I will discuss the mean pairwise momentum of clusters from the bulk velocity and the mass of simulated clusters, studying its variation as a function of the cluster mass and of the distance between pairs of objects and underscoring that the observability of the signal grows as the separation decreases.
In this seminar, I will describe the Holometer, a small experiment currently under construction at Fermilab to study gravitational microphysics at the Planck scale 10^-33 cm. Black hole thermodynamics already provides some clues to what form this microphysics might take. The Bekenstein-Hawking entropy formula suggests that all information in our universe may be stored holographically on 2-dimensional surfaces rather than in 3-dimensional volumes. Even more startling to our world-view is the notion this formula implies, that the universe has a bandwidth limit of 1 bit per Planck area. Philosophical issues aside, the universal bandwidth limit may produce diffractive effects which become observable when the diffraction is allowed to grow over macroscopic distances to magnify the Planck-scale fuzziness of space-time. The Holometer is a Michelson interferometer-based device optimized to detect the resulting, characteristic position noise spectrum of objects apparently at rest in the space-time. Its relatively small 40 meter size, compared to that of large gravitational wave detectors, allows flexibility of reconfiguration to probe detailed properties of the predicted holographic noise.
April 19, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar The Imprint of the Extragalactic Background Light in the gamma-ray spectra of blazars Marco Ajello, Space Sciences Laboratory, University of California Berkeley
The light emitted by stars throughout the history of the Universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL is important for understanding the nature of star formation and galaxy evolution. Direct measurements of the EBL are very difficult due to the intense zodiacal light and the Galactic foreground emission. High-energy gamma rays may interact with photons of the EBL and generate positron-electron pairs. This introduces an attenuation feature in the spectra of distant gamma-ray sources that has been used in the past to set upper limits on the opacity of the Universe and the energy density of the EBL. In this talk, we will report the first detection of an absorption feature seen in the combined spectra of a sample of gamma-ray blazars detected by the Fermi Large Area Telescope (LAT) out to a redshift of z>1.6. This feature is caused by attenuation of gamma rays by the EBL at optical to UV frequencies, and points to a minimal level of EBL, consistent with the observed star formation rate and with low-opacity EBL models. We will present the Fermi observations and discuss the implications for the generation of a diffuse UV background at high redshifts. We will also discuss recent measurements of the (nIR) EBL and present the prospects for a refined measurement of the EBL up to higher redshifts.
April 26, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Successes and Limitations of Cosmological N-body Simulations Raul Angulo, KIPAC, Stanford
In this talk I will discuss recent advances in simulating the spatial distribution and properties of galaxies in the Universe. I will start by showing how numerical simulations will help us to understand and exploit the precise measurements of upcoming galaxy surveys. As an example of this, I will discuss the predicted distortions in the baryonic acoustic oscillation signal when it is measured in the galaxy distribution. In the second part of my talk, I will discuss some limitations of N-body simulations and how some results might be misleading due to numerical artifacts. As an example of this, I will discuss the case of Warm Dark Matter cosmologies and I will present a possible solution to these problems.
May 3, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar The High Altitude Water Cherenkov Gamma Ray Observatory: Current Status and Future Prospects Thomas Weisgarber, University of Wisconsin - Madison
The High Altitude Water Cherenkov (HAWC) Observatory is currently under construction on the slopes of Sierra Negra in the Mexican state of Puebla. Scheduled for completion in August 2014, HAWC is designed to record air showers initiated by gamma rays and cosmic rays in the energy range from 100 GeV to 100 TeV. Of the full design of 300 water tanks, 30 are presently instrumented and have been taking data since September 2012. HAWC operates as a survey instrument with a large instantaneous field of view of 2 sr, complementing both ground-based gamma ray detectors such as VERITAS and space-based detectors such as the Fermi Telescope. I will summarize the design and construction of HAWC, discuss preliminary observations of the moon shadow and cosmic-ray anisotropy, and outline prospects for HAWC to contribute to gamma-ray and cosmic-ray science in the near future.
May 10, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Multiple-Field Inflation in the Post-Planck Era Joel Meyers, Canadian Institute for Theoretical Astrophysics
The results from the Planck satellite have provided excellent constraints on many cosmological parameters allowing us to constrain the physics of inflation. While all observations are currently consistent with the simplest models of inflation, many more complicated scenarios are also consistent with the data. In this talk, I will focus on the theoretical aspects of multiple field inflation in light of the Planck data. I will give particular attention to the local bispectrum which is tightly constrained by Planck giving us non-trivial information about the physics of the early universe.
May 17, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Final Results from Three Years of Observations with the BICEP Telescope Colin Bischoff, Harvard-Smithsonian Center for Astrophysics
The BICEP telescope, which operated at the South Pole from 2006 to 2008, was the first instrument designed specifically to search for inflation by targeting the B-mode polarization of the Cosmic Microwave Background at large angular scales. Results from the first two seasons, published in Chiang et al. (2010), have so far provided the tightest upper limits on B-modes. We report on new results that incorporate the full three year data set to improve this constraint. Besides including more data, the new analysis uses a novel method to deproject the largest source of systematic contamination in BICEP data.
The successful design of BICEP is the basis of BICEP2, which operated at the South Pole from 2010 through 2012, and the Keck Array, which began observations in 2011 and is still operating. These experiments are currently producing extremely deep maps of CMB polarization.
May 24, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar The Influence of Baryons in Interpreting the Cosmological Model Alyson Brooks, U Wisconsin Madison
The cosmological model based on cold dark matter (CDM) and dark energy has been hugely successful in describing the observed evolution and large scale structure of our Universe. However, at small scales (in the smallest galaxies and at the centers of larger galaxies), a number of observations seem to conflict with the predictions CDM cosmology, leading to recent exploration of Warm Dark Matter (WDM) and Self-Interacting Dark Matter (SIDM) models. These small scales, though, are also regions dominated by baryons. The more complex physics of baryons make them more difficult to model. I will show results from some of the highest resolution cosmological galaxy simulations ever produced that include both baryons and dark matter to show that baryonic physics can significantly alter the dark matter structure of galaxies, revolutionizing our expectations for the observed structure of galaxies. I will make the case that baryons have the potential to solve the crisis within CDM, but may also make it difficult to identify CDM vs WDM vs SIDM.
May 31, 2013 | 12:00 PM | LASR Conference Room | Friday noon seminar Low-mass WIMPs: Confessions of a Nihilist Juan Collar, The University of Chicago
I will review the present state of confusion concerning the ~10 GeV region in WIMP parameter space, with emphasis on the experimental uncertainties. Lots of those. We'll briefly allow ourselves to look at the light at the end of this tunnel (i.e., will discuss incoming information that should lead us out of the present impasse).
May 20, 2013 | 10:30 AM | LASR Conference Room | Open Group seminar The Continuing Story of Massive Gravity Rachel Rosen, Columbia University
Recent progress has led to the development of consistent theories of massive spin-2 particles. In this talk I will show how these theories lead naturally to theories of many interacting spin-2 particles. I will also discuss the search for a non-linear theory of "partially massless" gravity -- an exotic spin-2 representation with potential to address the cosmological constant problem.