2 October 2009	30 October 2009	4 December 2009
9 October 2009	6 November 2009	8 January 2010
16 October 2009	13 November 2009	15 January 2010
23 October 2009	20 November 2009

Tom Crawford, The University of Chicago

A preview of upcoming results from the South Pole Telescope  

The South Pole Telescope (SPT) is a 10-meter, millimeter-wave telescope operating at the Amundsen-Scott South Pole Station. The first camera on the SPT, a ~1000-element, three-color, bolometric receiver, has been operational since 2007 and is currently surveying hundreds of square degrees of the southern sky per year in observing bands centered on 90, 150, and 220 GHz. Analysis of the 2008 SPT data has resulted in several interesting discoveries and new results, which will be made public soon, and which I will give an informal survey of here. These results include the apparent discovery of a new population of star-forming galaxies, measurements of the SZ effect from known clusters out to unprecedented clustercentric radii, the first cosmologically interesting catalog of SZ-selected galaxy clusters, and measurements of high-l CMB power spectrum.

Dawn Erb, UCSB

Galaxies in the Young Universe: Metallicity, Kinematics, and Gas Flows  

A large fraction of the stars in the universe today formed during the redshift interval 1.5<z<3, when the universe was only about 25% of its current age. However, the quantitative study of galaxies in this redshift range from large spectroscopic samples has only recently become feasible. Such spectra offer a unique opportunity to quantify the physical conditions in these distant galaxies and their interactions with the surrounding intergalactic gas. I will discuss the results of a large near-IR spectroscopic survey of star-forming galaxies at z~2, highlighting the galaxies' kinematics, elemental abundances, and large-scale outflows and inflows of gas.

Ali Vanderveld, Caltech/JPL

Testing General Relativity on Cosmological Scales with Weak Gravitational Lensing  

Weak gravitational lensing is a powerful probe of modifications of General Relativity on cosmological scales, since such modifications can affect both how matter produces gravitational potential wells and how photons move within these wells. I will discuss alternative theories of gravitation and how we may constrain such theories using weak lensing observables, including those that could be obtained with the balloon-borne High Altitude Lensing Observatory (HALO). I will also discuss the ''parametrized-post-Friedmannian'' approach for obtaining model-independent constraints, in which new parameters are introduced to characterize the departure from General Relativity on large scales.

Jens Chluba, CITA

Signals from the Cosmological Recombination Epoch  

Very soon the Planck Surveyor will start observing the CMB temperature and polarization anisotropies with unprecedented precision. For the analysis of these data sets it will be very important to understand the ionization history of the Universe at redshift z~1100 with very high accuracy, since otherwise uncertainties in the modelling of the recombination process may lead to significant biases in the deduced values of some cosmological parameters. In addition to the simple fact that electrons are captured by protons and helium ions also some photons are released during the cosmological recombination process, leading to small distortions in the CMB blackbody spectrum which should still be present today. This recombination radiation carries valuable information about the dynamics of recombination and the underlying cosmological parameters, which until now has not been accessed. In my talk I will review some of the recent computations in connection with the ionization history of the Universe and the CMB power spectra, showing that neglecting details in the physics of recombination will lead to important biases in the values of n_s and Omega_b. Furthermore, I will try to show that one could learn a lot about cosmological parameter, details in the recombination dynamics, energy release at high redshift and possible dark matter annihilations during recombination by directly measuring the cosmological recombination radiation.

Andrew Wetzel, UC Berkeley

Satellite Galaxies in LambdaCDM: Orbits, Merging & Disruption  

Dark matter halos that merge with larger halos persist as subhalos, which host satellite galaxies. While subhalos are rapidly stripped of their dark mass, the compact luminous material remains intact longer, making the correspondence of galaxies with severely stripped suhalos unclear. I use a high-resolution, cosmological N-body simulation to explore satellite galaxy merging and tidal disruption. Satellite subhalos must be well-resolved down to ~1% of their mass at infall, and many satellites experience tidal disruption prior to merging with the central galaxy. Using abundance matching to assign stellar mass to subhalos, I compare with observed galaxy clustering, satellite fractions, and cluster luminosity functions. I also explore a simple analytic model based on dynamical friction for satellite infall. Finally, I examine the orbital distribution of infalling satellites and its evolution with halo mass and redshift.

Daniel Grin, California Institute of Technology

Cosmological hydrogen recombination: the effect of extremely high-n states and forbidden transitions  

Thanks to the ongoing Planck mission, a new window will be opened on the properties of the primordial density field, the cosmological parameters, and the physics of reionization. Much of Planck's new leverage on these quantities will come from temperature measurements at small angular scales and from polarization measurements. These both depend on the details of cosmological hydrogen recombination; use of the CMB as a probe of energies greater than 10^16 GeV compels us to get the ~eV scale atomic physics right.

One question that remains is how high in hydrogen principle quantum number we have to go to make sufficiently accurate predictions for Planck. Using sparse matrix methods to beat computational difficulties, I have modeled the influence of very high (up to and including n=200) excitation states of atomic hydrogen on the recombination history of the primordial plasma, resolving all angular momentum sub-states separately and including, for the first time, the effect of hydrogen quadrupole transitions. I will review the basic physics, explain the resulting plasma properties, discuss recombination histories, and close by discussing the effects on CMB observables.

Amit Yadav, Institute for Advanced Study, Princeton

Probing the Physics of the Beginning: Primordial Non-Gaussianity and Gravitational Waves  

In the last few decades, advances in observational cosmology have given us a standard model of cosmology. We know the content of the universe to within a few percent. With more ambitious experiments on the way, we hope to move beyond the knowledge of what the universe is made of, to why the universe is the way it is. In my talk, I will focus on what we can expect to learn about the dynamics of the universe at the very earliest moments. I will discuss theoretical predictions from inflationary models and their observational consequences in the cosmic microwave background anisotropies. In particular, I will focus on two observational signatures, primordial non-Gaussianity and gravitational waves, as probes for the physics of the beginning.

Simona Murgia, SLAC/KIPAC

Recent Results on Dark Matter Searches with Fermi  

The Fermi Large Area Telescope (LAT) has been successfully launched from Cape Canaveral on 11 June 2008. It is exploring the gamma ray sky in the energy range from 20 MeV to over 300 GeV with unprecedented sensitivity. One of the most exciting science questions that the Fermi LAT will address is the nature of dark matter. Several theoretical models have been proposed that predict the existence of Weakly Interacting Massive Particles (WIMPs) that are excellent dark matter candidates. The Fermi LAT investigates the existence of WIMPs indirectly, primarily through their annihilation or decay into photons and into electrons and positrons. I will present recent results on these searches.

Assaf Horesh, Tel-Aviv University

The lensing effciencies of X-ray versus optically selected galaxy clusters  

George Becker, Kavli Institute for Cosmology, Cambridge

Observational Signatures of Hydrogen and Helium Reionization  

The reionization of hydrogen and helium are intimately linked to the formation of the first galaxies and quasars, yet setting direct observational constraints on either process has proven to be highly challenging. Over the past few years, a variety of observations have started to shed lights on both. I will review progress made in the field, and discuss my group's recent work on metal enrichment by the first galaxies and the thermal history of the intergalactic medium. These studies are providing unique insights into the first three billion years of evolution in the IGM, and will complement upcoming observations in developing a consensus picture of hydrogen and helium reionization.

Jaiyul Yoo, Harvard University

New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects  

7 October 2009	28 October 2009	9 December 2009
14 October 2009	11 November 2009

Steven Allen, KIPAC (Stanford/SLAC)

X-ray Cluster Cosmology  

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.

Miguel A Mostafa, Colorado State University

The latest results from the Pierre Auger Observatory  

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.

Andrey Kravtsov, The University of Chicago

"Living on the Edges: Modeling Formation of the Smallest and Largest Luminous Systems in the Universe"  

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.

CANCELLED
Juan J Gomez-Cadenas, IFIC (CSIC-UV) SPAIN

Ettore Majorana meets his shadow  

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.

Claude Canizares, Massachusetts Institute of Technology

to be determined  

30 September 2009	4 November 2009	2 December 2009
21 October 2009	18 November 2009

Michael Gladders, University of Chicago

Strong Lensing by Optically-Selected Galaxy Clusters  

Gravitational lensing by galaxy clusters was predicted in the 1930s, and finally discovered in 1980s. In the two decades following the initial discovery, several dozen significant cluster lenses were found, though only a handful of these have been studied extensively. Lensing clusters probe the distribution of massive halos 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 halos. Most cluster strong lens studies to date have been 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 have found hundreds of new giant arcs. These efforts are now approximately three-quarters-complete; in this progress report I will describe some of the spectacular successes of these studies, and the remaining challenges.

Kip Thorne, California Institute of Technology

Gravitational Waves: A New Window onto the Universe  

Over the next decade or so, the gravitational-wave window onto the Universe will be opened in four frequency bands that span 22 orders of magnitude: The high-frequency band, 10 to 10,000 Hz (ground-based interferometers such as LIGO), the low-frequency band, 10^-5 to 0.1 Hz (the space-based interferometer LISA), the very-low-frequency band, 10^-9 to 10^-7 Hz (pulsar timing arrays), and the extremely-low-frequency band, 10^-18 to 10^-16 Hz (polarization of the cosmic microwave background). This lecture will describe these four bands, the detectors that are being developed to explore them, and what we are likely to learn about black holes, neutron stars, white dwarfs and early-universe exotica from these detectors' observations. [I will focus largely on LIGO and LISA but, unless you advise otherwise, I think it useful to include PTAs and CMB polarization as well.]

Josh Winn, MIT

Exoplanets and their Odd Orbital Orientations  

In the Solar system, the planets follow orbits that are aligned with the Sun's equatorial plane to within about 7 degrees. What about planets around other stars? Recently we have measured the orbital orientations (relative to their parent stars' equators) of more than a dozen different exoplanets, using a technique first theorized in the 19th century. Many systems have good alignment, as in the Solar system -- but there are a few surprises. I will discuss these results and their implications for theories of planet formation and migration.

Justin Khoury, University of Pennsylvania

Before the Big Bang  

This talk will explore the idea that our universe existed before the big bang, as an alternative to the standard big bang/inflationary model. I will show how a phase of slow contraction before the big bang can explain the observed degree of flatness and homogeneity of our universe, as well as generate a nearly scale-invariant spectrum of primordial density perturbations. I will contrast the predictions of this model with those of inflationary cosmology, and discuss observational prospects for distinguishing between the two scenarios.

Miguel Morales, University of Washington

Astronomy Colloquium  

1 December 2009

Guido D'Amico, SISSA

The effective theory of quintessence and its observational signatures  

I will study generic single-field dark energy models, by a parametrization of the most general theory of their perturbations around a given background, including higher derivative terms. In appropriate limits this approach reproduces standard quintessence, k-essence and ghost condensation. There are no general pathologies associated to an equation of state w_Q < -1 or in crossing the phantom divide w_Q = -1. Stability requires that, when w_Q < -1, dark energy behaves, on cosmological scales, as a fluid with a virtually zero speed of sound. Theoretical and stability constraints are summarized on the quintessential plane (1+w_Q) vs. speed of sound squared.
Finally, I will discuss the effect of dark energy with a zero speed of sound on non-linear scales, by calculating the halo mass function.