Measuring the Largest Angular Scale CMB B-mode Polarization with Galactic Foregrounds on a Cut Sky

We consider the e ectiveness of foreground cleaning in the recovery of Cosmic Microwave Background (CMB) polarization sourced by gravitational waves for tensor-to-scalar ratios in the range 0 < r < 0:1. Using the planned survey area, frequency bands, and sensitivity of the Cosmology Large Angular Scale Surveyor (CLASS), we simulate maps of Stokes Q and U parameters at 40, 90, 150, and 220 GHz, including realistic models of the CMB, di use Galactic thermal dust and synchrotron foregrounds, and Gaussian white noise. We use linear combinations (LCs) of the simulated multifrequency data to obtain maximum likelihood estimates of r, the relative scalar amplitude s, and LC coe cients. We find that for 10,000 simulations of a CLASS-like experiment using only measurements of the reionization peak (‘ 6 23), there is a 95% C.L. upper limit of r < 0:017 in the case of no primordial gravitational waves. For simulations with r = 0:01, we recover at 68% C.L. r = 0:012 +0:011 0:006 . The reionization peak corresponds to a fraction of the multipole moments probed by CLASS, and simulations including 30 6 ‘ 6 100 further improve our upper limits to r < 0:008 at 95% C.L. (r = 0:010 +0:004 0:004 for primordial gravitational waves with r = 0:01). In addition to decreasing the current upper bound on r by an order of magnitude, these foreground-cleaned low multipole data will achieve a cosmic variance limited measurement of the E-mode polarization’s reionization peak. Subject headings: cosmic background radiation ‐ cosmological parameters ‐ early universe ‐ gravitational waves ‐ inflation