April 6

Renee Hlozek (Princeton)

New Results fro the Atacama Cosmology Telescope

The Atacama Cosmology Telescope (ACT) has mapped the microwave sky to arcminute scales. Combining measurements made with ACT at 148 and 218 GHz with data from the Wilkinson Microwave Anisotropy Probe (WMAP), we recover the second through seventh acoustic peaks of the Cosmic Microwave Background anisotropy spectrum. We detect the presence of relativistic energy density at early times, and place limits on the power spectrum of initial conditions in the universe and models of inflation. We also measure the abundance of Helium and constrain the cosmic string tension in certain models.

In addition, the CMB illuminates all structures that formed since the Big Bang, providing other ways to study the evolution of the universe. The distribution of matter inferred purely from ACT observations of the gravitational deflection of CMB light, gives significant evidence for a dark energy component in the universe, independent of Type Ia Supernova data. ACT has discovered previously-unknown galaxy clusters, the largest bound objects in the Universe including an early cluster dubbed "El Gordo," is so massive that approximately only one such object at that epoch should be found on the entire sky, though just seven percent of the sky has been searched by ACT and similar instruments.

We will highlight the new results from ACT that open up a window to the early universe at small scales.