Feb 1

"Cosmic Voids as a Probe of Cosmology"
Jounghun Lee, Seoul National University, South Korea

Recent galaxy surveys have revealed that on the largest scale the Universe looks like a collection of bubble-like voids wrapped by filaments and sheets. The voids refer to the large almost empty regions in the Universe with extremely low number density of galaxies. In this talk I will explain how these cosmic voids can be a potentially powerful probe of the background cosmology. I will also describe the characteristic properties of the void galaxies and explain what new insights they can provide into the puzzle of the galaxy formation.

Feb 8

"Two Breakthroughs in Cosmic Shear Measurement (Weak Lensing)"
Jun Zhang, University of Texas at Austin

An important issue in weak gravitational lensing is about how to accurately measure the cosmic shear signals using galaxy images. The method has to work in the presence of the point spread function, the photon noise, the pixelation effect, etc.. In this direction, I have made two advancements recently:

1. I find (with a rigorous proof) that cosmic shear estimators do not exist in an ideal way, i.e., for each cosmic shear component, one cannot construct a single quantity from each galaxy image, whose ensemble average is the true shear. Alternatively, for each shear component, one can construct two quantities from each image, and the ratio of their ensemble averages yields the true shear. This conclusion demands a change in the way the n-point shear correlation functions are measured.

2. By extending the method in my earlier work, I have found that shear measurement can be made accurate to the second order in shear. This is important for cluster lensing mass measurement and future weak lensing surveys. The shear recovery accuracy in the newest version of my method can at least reach a sub-percent level in the presence of photon noise for galaxies and PSF's of arbitrary morphologies.

For both topics, I will provide numerical examples.

Feb 22

"The 7-year WMAP Observations: Cosmological Interpretation"
Eiichiro Komatsu, University of Texas at Austin, Director, Texas Cosmology Center

We have announced the results from 7 years of observations of the Wilkinson Microwave Anisotropy Probe (WMAP) on January 26. In this talk we will present the cosmological interpretation of the WMAP 7-year data, including the detection of primordial helium, images of polarization of microwave background around temperature peaks, and new limits on inflation and properties of neutrinos. We also report a significant detection of the Sunyaev-Zel'dovich effect and discuss implications for the gas pressure in clusters of galaxies.

Apr 12

"Can We Explain Core-Collapse Supernova Explosions?"
Adam Burrows, Princeton University, Tinsley Visiting Professor

At the intersection of much of 20th-Century physics, lies an astrophysical puzzle that has taxed theorists and computational science for almost half a century. Supernova explosions, the source of much of the heavy elements in the Universe and the birthplace of neutron stars and stellar-mass black holes, are still not understood. However, using sophisticated numerical tools and platforms, theorists have been able to conduct multi-dimensional simulations with increasing physical fidelity that have provided insight into the variety of phenonoma that attend stellar death and explosion. The core of the emerging theoretical synthesis is the centrality of asphericity and the breaking of spherical symmetry. In this talk, I will review the state of the field, the contending explosion models, and the connections with other exotic objects, such as gamma-ray bursts and hypernovae. In the process, I will highlight the state-of-the-art computational astrophysics which has been applied to date, and which may be necessary in the future, to credibly unravel this mystery.

Apr 19

PhD Defense: "Multidimensional Multiscale Dynamics of High-Energy Astrophysical Flows"
Sean Couch, University of Texas at Austin

Astrophysical flows have an enormous dynamic range of relevant length scales. The physics occurring on the smallest scales often influences the physics of the largest scales, and vice versa. I will discuss a detailed study of the multiscale and multidimensional behavior of jet-driven supernovae. Both theory and observations of core-collapse supernovae indicate these events are not spherically-symmetric; however, the observations are often modeled assuming a spherically-symmetric explosion. I present an in-depth exploration of the effects of aspherical explosions on the observational characteristics of supernovae. This is accomplished in large part by high-resolution, multidimensional numerical simulations of jet-driven supernovae.