1 October 2004	22 October 2004	12 November 2004
8 October 2004	29 October 2004	19 November 2004
15 October 2004	5 November 2004	3 December 2004

Ian McCarthy, University of Victoria

Harvard University 'Models of the ICM with Heating and Cooling: Explaining the Global and Structural X-ray Properties of Clusters'  

Non-radiative numerical simulations and self-similar scaling arguments fail to reproduce the observed X-ray scaling relations of clusters. As a result, there has recently been increased interest in models in which either radiative cooling or entropy injection (and/or redistribution) play a central role in mediating the thermal and spatial properties of the intracluster medium. Both sets of models produce results which have been shown to be in good agreement with the mean global properties of clusters. Radiative cooling alone, however, results in fractions of cold/cooled baryons in excess of observationally established limits. And, the simplest entropy injection models, by design, do not treat the ``cooling core'' structure present in many clusters and cannot account for declining entropy profiles towards cluster centers revealed by recent high resolution X-ray observations. We consider models that marry radiative cooling with entropy injection, and confront model predictions for the global and structural properties of massive clusters with the latest X-ray data. The models successfully and simultaneously reproduce the observed L-T and L-M relations, yield detailed entropy, surface brightness, and temperature. Profiles in excellent agreement with observations, and predict cooled gas fraction that is consistent with observational constraints. More interestingly, the model provides a possible explanation for the significant intrinsic scatter present in the L-T and L-M relations, which is crucial if clusters are to be used as probes for precision cosmology studies, such as the determination of sigma_8. Our model also offers a natural way of distinguishing between clusters classically identified as "cooling flow" clusters and relaxed "non-cooling flow" clusters. The former correspond to systems that experienced only mild levels (<300 keV cm^2) of entropy injection while the latter are identified as systems that suffered much higher entropy injection. The dividing line in entropy injection between the two categories corresponds roughly to the cooling threshold for massive clusters. This finding suggests that entropy injection may be an important, if not the primary, factor in determining which class a particular cluster will belong to. These results also suggest that the previously identified relationship between inferred cooling flow strength and the dispersion in the L-T relation is a manifestation of the distribution of entropy injections levels experienced by clusters. This is borne out by the entropy profiles derived from Chandra and XMM-Newton. Finally, we demonstrate that there is a tight observational trend between a cluster's central entropy and its core radius size which may also be accounted for by the model.

Naoshi Sugiyama, National Astronomical Observatory

Alternate Models for Reionization  

The evidence for early reionization from WMAP presents a challenge for the standard models for reionization. I will discuss several alternative ideas that might explain early reionization: decaying particles, non-Gaussian initial conditions, and isocurvature perturbations. I will also briefly summarize my recent work on a variety of other topics.

Beth Willman, University of Washington

The observed and predicted Milky Way satellite population  

Dorothea Samtleben, Kavli Institute for Cosmological Physics

CAPMAP and QUIET: Measuring the Polarization of the Cosmic Microwave Background  

CAPMAP is an experiment measuring the E-mode CMB Polarization in the l-range from 200 to 2000 with multiple W-band (90GHz) and Q-band (40GHz) correlation receivers on the 7m Crawford Hill telescope in NJ. Data has been taken for the past 2 years with 4 and then 8 receivers and we are about to deploy a total of 16 for this coming season. Experience from the last data taking periods, first results and the potential of CAPMAP will be presented. Plans for a large array, using miniaturized correlation polarimeters (QUIET), will be shown. QUIET intends to increase the sensitivity of current experiments to unprecedented precision, using in its first season 91 W-band receivers with a later upgrade to 1000.

Christopher Gordon, Kavli Institute for Cosmological Physics

Possible evidence for spatial fluctuations in dark energy.  

The WMAP cosmic microwave background (CMB) first year data was anomalously smooth on the largest spatial scales. We have recently shown that spatial fluctuations in the dark energy, that is causing the expansion of the Universe to speed up, may partially cancel the fluctuations in the CMB on the largest scales. This would imply that the residual fluctuations that are observed on large scales would be due to the integrated Sachs Wolfe effect which is caused by the effect of large scale structure on the CMB at a redshift of about 1. We found that the current WMAP data provides a two sigma detection of the dark energy fluctuations. As this effect only operates at and after about redshift of one, we predict that the EE polarization fluctuations will be unsuppressed on large scales. Reference: Christopher Gordon, Wayne Hu, astro-ph/0406496

Edward Baltz, Kavli Institute for Particle Astrophysics and Cosmology at Stanford University

Understanding Dark Matter: from Accelerators to Galaxies  

Many types of astronomical observations indicate that most of the clustering matter in the universe is non-baryonic and unobserved except for gravitational effects. This material seems to behave as a collisionless gas. Understanding the nature of this component is one of the biggest problems in physics. I briefly describe experimental efforts to understand dark matter, then describe a few recent theoretical developments that may help shed light on the issue.

Chris Vale, UC Berekeley

Weak Lensing and Dark Energy  

Since the first detection four years ago, weak gravitational lensing by large scale structure has emerged as an increasingly powerful probe of cosmology. I examine the current state of the art from a theorists point of view using numerical simulations, and speculate on the improvements that will be required if we are to constrain dark energy using future weak lensing surveys.

Jordi Miralda-Escude, Ohio State University

A new model for quasars and the M-sigma relation  

A quasar model is presented in which the accretion disk around the black hole is constantl replenished by matter from stars near the nucleus of a galaxy, as the stars are captured by the accretion disk and are destroyed inside it. The model implies a relation between the mass of the black hole and the central velocity dispersion of the stars that matches the observed relation.

Roman Scoccimaro, New York University

Galaxy Clustering: From HOD's to Brane-Induced Gravity  

I discuss how we can use galaxy clustering at large scales to constrain galaxy bias and the galaxy halo occupation distribution (HOD), the matter density from redshift-space distortions, primordial non-Gaussianity from inflation, and large-scale modifications of gravity that explain the acceleration of the universe.

6 October 2004	17 November 2004
20 October 2004	1 December 2004

Richard Ellis, Caltech

Detecting and Studying the Sources which ended the Dark Ages  

The final frontier in understanding the origin of stellar systems lies beyond a redshift of 5. Sources of ultraviolet radiation during this period of cosmic history may have played a key role in ending the "dark ages" when the bulk of hydrogen was neutral. The dominant radiating sources in this era will doubtless be faint and probably of low mass making their detection a considerable challenge. I will discuss various ways of making progress in this area with current facilities, prior to the completion of new facilities such as the James Webb Space Telescope and the Thirty Meter ground-based telescope.

Uros Seljak, Princeton University

Observational cosmology as a probe of fundamental physics  

I will review recent results from Sloan Digital Sky Survey (SDSS) on galaxy clustering, weak lensing and Ly-alpha forest. In combination with WMAP results on cosmic microwave background these tracers of large scale structure give us an unprecedented view of the universe over a broad range of scales and epochs. I will describe how we can test fundamental theories of the universe with these observations, focusing on three questions: do neutrinos have mass? what provided initial seeds of structure in the universe? what is the nature of the dark energy? Existing data and corresponding analyses already greatly improve the precision of these tests, which will be improved further in the future. The progress in observations requires a parallel progress in our theoretical understanding of astrophysical processes such as physics of galaxy formation and physics of inter-galactic medium. I will describe recent developments in these areas.

Allison Coil, UC Berkeley

First Large-Scale Structure Results from the DEEP2 GalaxyRedshift Survey: Galaxy Clustering, Environment, Groups and Voids at z=1  

I will discuss the first large-scale structure results from the z=1 DEEP2 Galaxy Redshift Survey. We study both galaxy clustering and environment as a function of color, spectral type, and luminosity and find that red, absorption-dominated, passively-evolving galaxies are more strongly clustered than blue, emission-line, actively star-forming galaxies. The implied galaxy bias in our sample is b~1.0-1.2. I will show initial results on the relationship between galaxy properties and environment in the DEEP2 sample and compare our results to similar studies recently completed in the SDSS. Finally, I will present our first group catalog and our measured void probability distribution function and discuss their implications.

Andrew Hamilton, University of Colorado, Boulder

Inside Black Holes  

What really happens inside black holes? If you fell into one, what would you see, what would you experience? It is well known that, except for the single case of the Schwarzschild solution, the vacuum solutions for the interiors of black holes are inconsistent as endpoints of gravitational collapse, because the cores of vacuum black holes are gravitationally repulsive. Instead, black holes must contain matter. In this talk I consider self-similar solutions for charged spherical black holes, taking charge as a surrogate for angular momentum. The black holes are allowed to accrete a mix of baryons and non-baryonic Dark Matter. I show how details such as the electrical conductivity, and the cross-section for interaction between baryons and Dark Matter, play crucial roles in determining the internal structure of a black hole, which proves to be surprisingly complex. Real time visualizations of such black holes will be shown.

21 October 2004	18 November 2004
11 November 2004	2 December 2004

Jeremy Tinker, Ohio State University

Constraining Cosmology with the Halo Occupation Distribution  

The halo occupation distribution (HOD) is a method of characterizing bias by parameterizing the occupation of galaxies within dark matter halos. It has been used effectively to model the correlation function for SDSS galaxies. These models make predictions for other statistics and measures that depend on the assumed cosmology. In my talk I will apply these HOD models to dynamical measures which are sensitive to the underlying mass scale of halos. Specifically, I will focus on mass-to-light (M/L) ratio of clusters, and redshift-space distortions of the correlation function. For M/L ratios, I will show that the observed clustering and M/L values imply constraints on Omega_m and sigma_8 that are in conflict with the concordance model. For redshift-space distortions, I will present numerical results based on HOD analysis and a calibrated analytic model. Preliminary comparisons to SDSS data agree with the implications of the M/L results to best match observations, either sigma_8 or Omega_m needs to be lower than their concordance values of 0.9 and 0.3.

Alexander Conley, UC Berkeley

Measurement of $Omega_m$, $Omega_{Lambda}$ from an analysis of Type Ia supernovae with CMAGIC: Using color information to check the acceleration of the Universe  

Several years ago, measurements of the apparent luminosity of distant Type Ia supernovae resulted in the surprising discovery that the acceleration of the Universe is accelerating. Because of the profound effect this has on our knowledge of the future fate of the Universe, as well as on our understanding of fundamental physics, it is extremely important to attempt to cross-check this result. In this talk I will discuss some of the outstanding concerns about these measurements, and describe a new technique (CMAGIC) (first introduced in Wang '03) for fitting multi-color lightcurves of SNe Ia which has several advantages over more standard maximum magnitude techniques with respect to these concerns.I will then describe a blind analysis of current supernova data using CMAGIC, which allows me to provide a powerful cross-check of previous supernova results.

Joanna Dunkley, Oxford University

Non-adiabatic models: CMB constraints using fast MCMC  

Stelios Kazantzidis, Institute for Theoretical Physics, U. Zurich, Kavli Instiute of Chicago, (KICP)

The Effect of Baryons on Cosmic Structures  

The effect of baryons on cosmic structures is investigated using high-resolution gasdynamical simulations of galaxies and clusters in the LCDM cosmology combined with controlled numerical experiments. In particular, I will discuss the vital role of baryons for crucial issues in galaxy formation research, including the fate of supermassive black holes and the evolution of the M(BH)-sigma relation in binary disk galaxy mergers, the structural evolution of substructure in cold dark matter models, and the shapes of dark matter halos. I will argue that baryons play a role out of proportion to their relatively modest contribution to the total mass,thus making them essential for understanding the formation and evolution of structure in the Universe and comparing theory with observations.

7 December 2004

Yago Ascasibar, Center for Astrophysics, Harvard

Numerical simulations of cluster mergers  

In this talk, I suggest that minor mergers may produce structures that resemble the "cold fronts" (contact discontinuities) observed in the cores of apparently relaxed systems. I will also discuss the possibility of tracing the evolution of substructure in clusters (or galaxies) by means of halo finder in phase space. Such algorithm, dubbed HOT+FiEstAS, can also be applied to more general classification problems, both supervised and unsupervised(e.g. finding clusters in observational surveys, selecting AGN,or filtering spam).