Special Astrophysics Seminar

The Cosmology Large Angular Scale Surveyor (CLASS)

Katie Harrington

John Hopkins

The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to detect and characterize relic primordial gravitational waves from inflation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on large angular scales. The frequency bands of the CLASS telescopes, one at 40 GHz, two at 90 GHz, and one dichroic system at 150/220 GHz, are chosen to avoid regions of high atmospheric emission and span the minimum of the polarized galactic foregrounds: synchrotron emission at lower frequencies and polarized dust emission and higher frequencies. Low noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique level of high sensitivity, stability, and control of systematics. The CLASS site, at high altitude in the Chilean Atacama desert, allows for daily mapping of up to 70% of the sky and enables the observation of the largest angular scales. Using this combination of a broad frequency range, large sky coverage, control over systematics, and high sensitivity, CLASS will observe the reionization and recombination peaks of the CMB E- and B-mode power spectra. CLASS will make a cosmic variance limited measurement of the optical depth to reionization and will measure or place upper limits on the tensor-to-scalar ratio, r, down to a level of 0.01 (95% C.L.).