Talks & Events
KICP Friday Noon Seminars: 2010
The Atacama Cosmology Telescope: Spectrum and parameters from the 2008
The Atacama Cosmology Telescope (ACT) has mapped the microwave sky to arcminute scales. We will present the spectrum at 148 and 218 GHz from the 2008 season of the Southern Survey of the Atacama Cosmology Telescope. Improved map-making and efficient spectrum estimation allow us to recover the second through seventh acoustic peaks, and provide independent confirmation of the LCDM paradigm. After discussing the telescope and tests of the spectra, we will describe constraints on both primary cosmological parameters and secondary parameters from the small-scale power spectrum, including diffuse SZ emission and foregrounds.
How uncertain is our interpretation of cosmic ray data at high energy?
Precision Cosmology from Optical Galaxy Clusters
Dark energy constraints from future optical galaxy cluster surveys will depend on how various systematic errors are controlled. I will first focus on the observable-mass distribution, discussing self-calibration and follow-ups for constraining cluster mass. I will then talk about theoretical uncertainties, discussing how precise calibrations of the dark matter halo mass function, bias function, and assembly history using N-body simulations will impact precision cosmology.
Results from the ANITA Search for Ultra-High Energy Neutrinos
The ANITA (ANtarctic Impulsive Transient Antenna) experiment is a balloon-borne radio telescope, designed to detect coherent Cherenkov emission from cosmogenic ultra-high energy neutrinos with energy greater than 10^18 eV. The second flight of the ANITA experiment launched on December 21st, 2008, and collected data for 30 days. This new data set allows for the most sensitive search to date for GZK neutrinos, which would reveal information about the source of the highest energy cosmic rays. I will present the results from the second flight of ANITA and discuss calibration techniques, analysis methods, and background rejection.
Constraining the dawn of cosmic structure and the epoch of reionization with the 21 cm line
The first billion years of the Universe contains the formation of the first galaxies and reionization. This period lies beyond the current observational frontier presenting challenges to theory and observation. Low frequency observations of the redshifted 21 cm line of neutral hydrogen will be key in developing our understanding of this period. In this talk, I will describe two aspects of the 21 cm signal from the period of ''cosmic dawn'': the global 21 cm signal and 21 cm fluctuations. I will discuss what can be learnt about the first galaxies and reionization from this technique and explore some of the challenges and opportunities ahead for the first observations.
Low Threshold Dark Matter Search Using Charge Coupled Devices
The IMF, the UV bump, and AGB stars: New Insights From Stellar Population Synthesis
Stellar population synthesis (SPS) combines stellar evolution and atmosphere calculations, an initial mass function, a dust model, and a star formation history in order to `predict' the emergent spectrum of a galaxy. SPS techniques have proliferated in the past decade, resulting in the routine estimation of stellar masses, star formation rates, and metallicities of large samples of galaxies. In this talk I will focus instead on the basic SPS ingredients, including the IMF, dust properties, and evolution of AGB stars, and demonstrate that these uncertain inputs can actually be constrained directly from the integrated light of galaxies. By confronting a flexible SPS model with a variety of data, I will show that the low-mass IMF is not universal, the 2175A dust feature seen in our Galaxy also exists in typical star-forming galaxies, and that AGB stars contribute substantially less light in the near-IR than state-of-the-art stellar evolution calculations predict. Implications of these results will also be highlighted.
Simulations of the Magellanic Stream in a First Infall Scenario
Recent high precision proper motions from the Hubble Space Telescope (HST) suggest that the Magellanic Clouds are either on their first passage or on an eccentric long period (>6 Gyr) orbit about the Milky Way (MW). This differs markedly from the canonical picture in which the Clouds travel on a quasi-periodic orbit about the MW (period of ~2 Gyr). Without a short period orbit about the MW, the origin of the Magellanic Stream, a young (1-2 Gyr old) coherent stream of HI gas that trails the Clouds ~150 degrees across the sky, can no longer be attributed to stripping by MW tides and/or ram pressure stripping by MW halo gas. We propose an alternative formation mechanism in which material is removed by LMC tides acting on the SMC before the system is accreted by the MW. Both Clouds are modeled as N-body systems using cosmologically motivated density profiles and infall masses. The orbit of the SMC about the LMC is chosen such that resonances maximize the efficiency of LMC tides. Contrary to previous models, the orbit of the LMC about the MW is not assumed to be a free parameter and is instead determined by the HST proper motions. The N-body simulations demonstrate that it is possible to explain the origin of the Stream under the assumption that the Clouds have not been long term satellites of the MW. More generally, they show that gas stripping is expected to occur between any gas-rich dwarf galaxy pair.
Overcoming astrophysical uncertainties to constrain fundamental physics with LSS measurements
Large scale structure (LSS) measurements complement CMB observations in constraining fundamental physics parameters, such as neutrino properties and non-Gaussianity. However, our uncertainties in how galaxies trace the underlying matter density field complicate our interpretation of LSS observations in terms of these fundamental parameters. I will discuss how these uncertainties were (partially) overcome in our analysis of the SDSS Luminous Red Galaxy sample. In the second part of the talk, I will show that a dependence of galaxy properties on its host halo's assembly history can introduce significant uncertainties in the interpretation of large-scale clustering in terms of the non-Gaussianity parameter f_NL.