Feb 27

"String Axions and other Bosons: New Prospects for Astronomical Constraints on Ultra-Light Particle Dark Matter"
Tanja Rindler-Daller, University of Texas at Austin

Various extensions of the Standard Model of Particle Physics predict the existence of ultra-light bosonic particles, ranging from about 1 eV down to 10^(-33) eV. These particles form a Bose-Einstein condensate within a substantial part of the particle parameter space, determined by mass and possibly self-interaction coupling strength, and are plausible candidates for part or all of the cold dark matter (CDM) in the Universe. I will present an overview on how these CDM candidates can be constrained by current and future cosmological and astronomical observations. I will particularly focus on the mass window between around 10^(-25) - 10^(-21) eV, in which particles exhibit quantum coherence on the scales of galactic halos. Thereby, these alternative dark matter models can resolve the shortcomings of standard CDM on small scales, while preserving its success on large scales. The differing nature of this form of dark matter results in characteristic imprints on the galactic dynamics with potentially observable consequences. I will review expected signature effects, including our own work on the formation of vortices and their effects in rotating halos, as well as work in progress on halo formation scenarios with this form of dark matter.

Mar 26

"Measuring the Large-Scale Flow of X-ray Luminous Clusters from WMAP Data"
Alexander Kashlinsky, NASA, Goddard Space Flight Center (TCC Visiting Speaker)

In standard cosmological paradigm, large-scale peculiar velocities arise from gravitational instability due to mass inhomogeneities seeded during inflationary expansion. On sufficiently large scales, > 100 Mpc, this leads to a robust prediction of the amplitude and coherence length of these velocities independently of cosmological parameters or evolution of the Universe. For clusters of galaxies, their peculiar velocities can be measured from the kinematic component of the Sunyaev-Zel'dovich (SZ) effect produced by Compton scattering of cosmic microwave background (CMB) photons off the hot intracluster gas. I will discuss results from new measurements of the large scale peculiar flows using a large X-ray cluster catalog and all-sky CMB maps from the WMAP satellite. The results cast doubt that the gravitational instability from the observed mass distribution is the sole - or even dominant - cause of the detected motions. Instead it appears that the flow extends across the observable Universe and may be indicative of the primeval preinflationary structure of space-time and its landscape.

Apr 16

"Kinetic Sunyaev-Zel’dovich Effect as the Probe of the Reionization Epoch"
Hyunbae Park, University of Texas at Austin

We present a calculation of the kinetic Sunyaev-Zel'dovich (kSZ) effect on of the Comic Microwave Background fluctuation. We focus on the scale at the multipole moment of l = 3000 ~ 10000 that is currently being probed by the South Pole Telescope (SPT) and the Atacama Cosmology Telescope. For the post-reionization contribution of the total signal, we use the 3rd order perturbation theory (3PT) to model non-linearity of post-reionization epoch. We evaluate a non-linear expression for momentum powerspectrum in Ma and Fry (2002) with the 3PT density and velocity powerspectrum. And, we use the 3PT momentum powerspectrum to calculate the kSZ signal. We show that the 3PT is a reasonable approximation by comparing our result with previous work by Zhang, Pen and Trac (2004). For reionization contribution, we use our N-body radiative transfer simulations to take patchiness of ionization of intergalactic medium in reionization epoch into account. Using ionized fraction field in the simulation, we calculate the momentum field of the ionized gas. And, we correct for the missing power in finite size boxes of simulations. Finally, we show the kSZ calculation for different simulations with reionization scenarios. With contributions from each epoch, we predict total kSZ signal for different reionization history and put constraint on reionization scenario using an upper bound of the signal from recent SPT measurement.

Apr 23

"New Probes of Weak Lensing"
Fabian Schmidt, California Institute of Technology (TCC Visiting Speaker)

Weak gravitational lensing is one of the most promising observational tools in cosmology, as it measures the underlying total matter distribution rather than just the luminous baryonic matter. Commonly, weak lensing is measured using shear through galaxy ellipticities, or using the effect of magnification bias on galaxy number densities. I will report on the first detection of weak lensing magnification with a new, independent technique using the distribution of galaxy sizes and magnitudes. Our first application of this technique to an X-ray selected sample of galaxy groups in the COSMOS HST survey yields results consistent with shear measurements, and at roughly 40% of the signal-to-noise of the latter. I will discuss systematic issues and challenges to realizing the potential of this new probe of weak lensing.

May 7

"The First Dwarf Galaxies: Assembly of Disks and the Start of Reionization"
Andreas Pawlik, University of Texas at Austin

The first galaxies are thought to have started the reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present ionized state that occurred during the first few hundred million years after the Big Bang. Reionization is a watershed event in the history of galaxy formation and evolution. A number of observational projects are therefore underway to unravel the astrophysics at these early times. Prominently amongst them is the James Webb Space Telescopes (JWST), which will hunt for the light from the first galaxies. Cosmological simulations are the most powerful tools for gaining theoretical insight into the properties of the first galaxies that is urgently needed to interpret the upcoming observations. I will present results from zoomed cosmological simulations of the assembly of galaxies in halos reaching masses as large as one billion solar as early as five hundred million years after the Big Bang. These so-called first dwarf galaxies are thought to be amongst the main drivers of reionization. A characteristic outcome of the simulations is the assembly of rotationally supported galactic disks. I will address the impact of feedback from star formation on the disk assembly and discuss the prospects for observations of the first galaxies with the JWST.