Talks & Events
KICP Colloquia: 2009
Charged Cosmic Rays and Dark Matter
Dan Hooper, Fermilab/U Chicago
Recent results from the PAMELA and ATIC experiments have lead us to the conclusion that highly relativistic (10-600 GeV) electrons and positrons are surprisingly ubiquitous in cosmic ray spectrum. Although the source of these unexpected particles is currently not known, an exciting possibility is that they might be the product of dark matter particles annihilating in the local halo of the Milky Way. I will discuss what it would take for dark matter to produce these signals, and the future measurements that will enable us to identify the origin of these particles once and for all.
GLAST, HESS and Beyond, Status and Future of Gamma-ray Astronomy
Stefan Funk, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
The field of gamma-ray astronomy has received considerable attention beyond the high-energy astrophysics community in the recent years. This is in part due to the success of Imaging Atmospheric Cherenkov Telescopes such as HESS, MAGIC and VERITAS measuring gamma-rays in the energy regime above 100 GeV. All these new facilities have lifted gamma-ray astronomy in the last few years from an exotic discipline with a handful of detected sources to a solid astronomical discipline. In addition, the recent launch of the Fermi Space Telescope (FST) and its main instrument, the Large Area Telescope (LAT) measuring gamma-rays outside Earth's atmosphere the energy range beyond 100~MeV adds to the attention and excitement. The Fermi-LAT instrument will solidify the field by detecting several thousands of new sources and by bridging the energy spectra of ground-based detected VHE gamma-ray sources to well-studies objects at X-ray energies. In this seminar I will discuss the current status of the field, as well as the potential for future observatories.
Precision Cosmological Constraints from Optically-Selected Clusters
Risa Wechsler, KIPAC / Stanford University
I will present new constraints on the matter density and clustering amplitude of matter in the Universe,
based on the largest galaxy cluster catalog available to date, the SDSS maxBCG cluster catalog. When combined with CMB data, these data improve the precision of the parameter constraints by a factor of two, with comparable accuracy to the most recent determinations from X-ray clusters. Our analysis is fully self-calibrated in the sense that we do not rely on a priori determinations of the relation between the number of galaxies in a cluster and a cluster's mass. I will discuss how this approach can be extended to the next generation of photometric surveys, focusing on the Dark Energy Survey. I will discuss which aspects of the future survey are most critical, highlighting the role of uncertainties in the mass-observable relation
and the power of well-selected followup observations to improve the dark energy constraints.
Neutrinos and the dark side of the light fermions
Alexander Kusenko, UCLA
The past decade has been marked by some remarkable discoveries in the neutrino physics: the particles once believed to be massless have turned out to be massive and have shown evidence of lepton family number violation, as well as other interesting phenomena. While this is exciting, the future may hold even more dramatic discoveries, the hints for which begin to appear in astrophysics and cosmology. The observed neutrino masses imply the existence of some yet undiscovered "right-handed" states, which can be very massive and unreachable, but which can also be light enough to constitute the cosmological dark matter and to account for a number of astrophysical phenomena, from supernova asymmetries and the pulsar kicks to the peculiarities in the reionization and formation of the first stars. I will review the recent progress in neutrino physics, as well as the clues that may lead to future discoveries.
Recent Results from IceCube
Teresa Montaruli, University of Wisconsin - Madison
After two more construction seasons IceCube, the first cubic-kilometer
neutrino telescope, will be completed as initially planned. The instrumentation of this extremely large volume allows to measure neutrinos in the energy range from about 100 GeV up to energies larger than 10^17 eV. IceCube will reach sensitivites well below expected neutrino fluxes from astrophysical sources accelerating hadrons. A ground-based extensive air-shower, IceTop, measuring showers induced by primaries of energy between 10^15 - 10^17 eV, enriches the physics potential of this observatory at the South Pole operating standalone and in coincidence with the deep ice detector.
The current results of IceCube in incomplete configurations and the physics reach of the full detector will be discussed as well as the low energy extension DeepCore and possible high energy extensions.
The Radio Background from ARCADE 2
Dale J. Fixsen, University of Maryland
The ARDCADE 2 instrument has measured the absolute temperature at 3-90 GHz, with an open aperture cryogenic instrument observing at balloon altitudes with no windows with an in situ blackbody reference. The radio background is larger than expected with a temperature of 1.2 K at 1 GHz with an index of -2.6. Then CMB temperaure agrees with FIRAS.
Dark Stars, or the Effect of Dark Matter on the First Stars
Paolo Gondolo, University of Utah
The first stars in the universe may have been powered by dark matter heating rather than nuclear fusion. They were dark matter-powered stars, or for short Dark Stars. The annihilation of weakly interacting massive particles would provide the heating. This talk presents the story of Dark Stars: how they form, how long they might live, and what they might become at the end of their lives.
Early Results from the Fermi Large Area Telescope Gamma-ray Sky Survey
Rob Cameron, SLAC/KIPAC
The Fermi Gamma-ray Space Telescope was launched in June 2008. The Large Area Telescope (LAT) instrument on Fermi is designed to study the gamma-ray sky in the energy range from 20 MeV to 300 GeV. The first year of the Fermi mission is devoted to a full sky survey with the LAT, started in August 2008. I will summarize the Fermi mission capabilities and report on the survey progress with details of some interim science results.
Cosmology and Astrophysics with Galaxy Clusters
Daisuke Nagai, Yale University
Clusters of galaxies are unique probes of cosmology and astrophysics, promising to provide new insights into both the nature of dark energy and dark matter and the physics of galaxy formation. One of the key challenges facing this approach lies in our understanding of cluster physics and their impact on cluster structure and evolution. In this talk, I will review recent development of theoretical and computational modeling of galaxy cluster formation, with focus on thermodynamic of intracluster medium. Numerical simulations including gas cooling and star formation reproduce global properties of the intracluster medium (ICM) and observable-mass relations with the accuracy of ~10%. I will show that non-thermal processes, such as turbulence, cosmic-rays, and ICM plasma physics, are the dominant sources of systematic uncertainties in the current cluster mass estimate. I will discuss the future prospect for improving our understanding of cluster astrophysics and cosmological constraints with upcoming large-scale cluster surveys.
Radio detection of extensive air showers
Joerg R Hoerandel, Radboud University Nijmegen
The origin of cosmic rays, among them being the highest energy particles in the Universe is one of the main open questions in Astroparticle Physics. Air showers are induced by interactions of high-energy cosmic rays in the atmosphere. Secondary electrons (and positrons) are deflected in the Earth's magnetic field and emit synchrotron radiation. This radio emission is detected by dipole antennas. The technique has been pioneered by the LOPES experiment, operated in coincidence with the KASCADE-Grande air shower experiment.
Radio emission of ultra high-energy cosmic particles offers a number of interesting advantages. Since radio waves suffer no attenuation, radio measurements allow the detection of very distant or highly inclined showers, can be used day and night, and provide a calorimetric measure of the electromagnetic shower component.
The LOPES experiment has detected the radio emission from cosmic rays, confirmed the geosynchrotron effect for extensive air showers, and provided a good calibration formula to convert the radio signal into primary particle energy. Future steps will be the installation of a 20 km^2 radio antenna field at the Pierre Auger Observatory to measure the composition of cosmic rays in the energy region between 10^17 and 10^18 eV. In this region a transition from galactic to extra-galactic origin of the particles is expected. Prototype studies are presently conducted on site in Argentina. Future activities also include the use of the LOFAR radio telescope as cosmic-ray detector. The LOFAR telescope is presently constructed in the Netherlands and in Europe as a digital radio interferometer.
The present status of the activities is reviewed and the perspectives will be discussed. It is expected that the radio technique will develop into a mature and independent method to detect ultra high-energy cosmic rays within the next decade.
Strong Lensing by Optically-Selected Galaxy Clusters
Mike Gladders, The University of Chicago
Gravitational lensing by galaxy clusters was predicted in the 1930s, and finally discovered in 1986. Since these initial discoveries, several dozen significant cluster lenses have been discovered in a variety of ways.
Lensing clusters probe the distribution of massive haloes in the universe; the expected arc production frequency can be predicted from simulations and compared to existing data. Massive lensing clusters act as 'natural telescopes', providing highly magnified images of background sources which cannot otherwise be studied using the current generation of telescopes.
The details of the observed lensing in clusters also probes the internal properties of these massive haloes. Most cluster strong lens studies to date have been rather limited by the small number and heterogeneous nature of the sample of known lenses (most of which are one-off discoveries). I will report on efforts to take the study of strong lensing clusters to a new statistical regime, by identifying and studying two new samples of strong lenses within large catalogs of optically selected galaxy clusters from the RCS-2 and SDSS surveys. In total we expect to find hundreds of new giant arcs. These efforts are now approximately half-complete; in this mid-course report I will describe some of the successes of these studies, and the remaining challenges. Time permitting, I will also discuss a recently commissioned instrument at the Magellan telescopes which was designed specifically for studying these new lens samples.
X-ray Cluster Cosmology
Steven Allen, KIPAC (Stanford/SLAC)
X-ray observations of galaxy clusters provide powerful cosmological constraints via two independent methods. The first uses measurements of the baryonic mass fraction in the largest, dynamically relaxed clusters. This method, like type Ia supernovae studies, measures distance as a function of redshift and traces the acceleration of the Universe directly. It also provides a tight constraint on the mean matter density. The second method uses the observed evolution of the cluster mass function. It leads to tight constraints on the amplitude of mass fluctuations and powerful, complementary constraints on dark energy. I will present the latest results from our team's work using both methods, employing a rigorous, self-consistent approach that accounts for survey biases, captures fully the important degeneracies between parameters and includes conservative allowances for systematic uncertainties. I will place the results in context with other current experiments and highlight the prospects for improvements in the near-to-mid term with the incorporation of new SZ, optical and X-ray data and improved hydrodynamical simulations.
The latest results from the Pierre Auger Observatory
Miguel A Mostafa, Colorado State University
Since the first detection of a cosmic ray event with energy above 1020 eV in 1962, their nature and origin remain unknown. Due to the extreme rarity of these ultra high energy cosmic rays, they must be observed indirectly through the observation of extensive air showers, and the lack of knowledge of hadronic interactions at these energies leads to inherent difficulties in characterizing the properties of the primary particle.
A new generation cosmic ray detector, the Pierre Auger Observatory, has been designed to study cosmic rays with energy above 1018 eV and answer the crucial questions of ultra high energy cosmic ray physics. The Southern Observatory in Argentina has been collecting data since January 2004, and its exposure is larger than that of any other cosmic ray experiment. Among the first results from the Pierre Auger Collaboration are the most precise measurement of the suppression of the cosmic ray flux at the highest energies, the first anisotropy result above 6 x 1019 eV, the first photon limit with a fluorescence detector, and the best neutrino limit at EeV energies. Then, after five years of operation, a good question is, "What is left to be done?" In this colloquium, I will describe the Pierre Auger Observatory in its astrophysical context, our most recent results, and the exciting prospects for the near future.
"Living on the Edges: Modeling Formation of the Smallest and Largest Luminous Systems in the Universe"
Andrey Kravtsov, The University of Chicago
The current Cold Dark Matter paradigm of structure formation in the universe has proven its mettle in numerous stringent tests against observations over the last three decades. Nevertheless, many aspects of the theory related to the physics of baryonic component of galaxies and galaxy clusters remain relatively poorly understood and are therefore subject to continuous rigorous testing.
In this talk, I will focus on formation of the smallest luminous galaxies (some of which contain only a few hundred stars) and the largest virialized systems - galaxy clusters. These systems occupy extremes of the mass range of collapsed objects and are interesting from both astrophysical and cosmological standpoints. The faintest dwarf galaxies give us a window into the process of star formation and stellar feedback in extremely low density and low metallicity environments and, at the same time, provide constraints on the properties of dark matter particles. Clusters of galaxies are excellent laboratories for studying details of galaxy formation and interaction of galaxies with surrounding gas and, at the same time, can be used as sensitive probes of cosmological parameters. I will review some of the recent research developments in modeling these systems and will discuss implications both for our understanding of galaxy formation and for cosmology.
Ettore Majorana meets his shadow
Juan J Gomez-Cadenas, IFIC (CSIC-UV) SPAIN
Seventy years have elapsed since Majorana's bold hypothesis about the neutrinos, and almost the same time since he dissappeared in misterious circunstances, a mistery yet as unresolved as the true nature of Neutrino. Probably we will never know what happened to the physicist but neutrinoless double deta decay experiments may unravel if the neutrino is its own antiparticle. I will offer a brief review of the satus of the field and the most promising techniques for the NEXT generation of experiments.
Searching for 'Missing Baryons' in the Warm-Hot Intergalactic Medium with High Resolution X-ray Spectroscopy
Claude Canizares, Massachusetts Institute of Technology
Baryons make up 4.6% of matter and energy content of the universe, but roughly half the baryons in the current epoch have not yet been observed. Simulations suggest that the missing matter is primarily in a "cosmic web" of hot, low-density plasma that traces the large-scale structure of the universe. At temperatures above 106 K, the most promising signature of this so-called WHIM is the resonance line of He-like oxygen, O VII He α, around 20 Å. This line can be observed in absorption against background X-ray point sources with the high resolution spectrometers on the Chandra and XMM-Newton observatories (an X-ray analog to the Ly α forrest). The observations, however, are challenging and results have been controversial. This talk will review evidence for (and against) the detection of the WHIM, including a recently confirmed observation of an X-ray absorption line associated with the large-scale galaxy enhancement in the direction of Sculptor.