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Register a new userBICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
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The Keck Array is a system of cosmic microwave background (CMB) polarimeters, each similar to the BICEP2 experiment. In this paper we report results from the 2012 and 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as BICEP2. We again find an excess of B-mode power over the lensed-$Lambda$CDM expectation of $> 5 sigma$ in the range $30 < ell < 150$ and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with BICEP2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 $mu$K arcmin) over an effective area of 400 deg$^2$ for an equivalent survey weight of 250,000 $mu$K$^{-2}$. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of $> 6sigma$.
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(abridged for arXiv) We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around $ellsim80$. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of $approx300mumathrm{K}_mathrm{CMB}sqrt{s}$. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes $Q$ and $U$. We find an excess of $B$-mode power over the base lensed-LCDM expectation in the range $30< ell< 150$, inconsistent with the null hypothesis at a significance of $> 5sigma$. Through jackknife tests and simulations we show that systematic contamination is much smaller than the observed excess. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power $sim(5-10)times$ smaller than the observed excess signal. However, these models are not sufficiently constrained to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed and its spectral index is found to be consistent with that of the CMB, disfavoring dust at $1.7sigma$. The observed $B$-mode power spectrum is well fit by a lensed-LCDM + tensor theoretical model with tensor-to-scalar ratio $r=0.20^{+0.07}_{-0.05}$, with $r=0$ disfavored at $7.0sigma$. Accounting for the contribution of foreground dust will shift this value downward by an amount which will be better constrained with upcoming data sets.
We present measurements of polarization lensing using the 150 GHz maps which include all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including the 2014 observing season (BK14). Despite their modest angular resolution ($sim 0.5^circ$), the excellent sensitivity ($sim 3mu$K-arcmin) of these maps makes it possible to directly reconstruct the lensing potential using only information at larger angular scales ($ellleq 700$). From the auto-spectrum of the reconstructed potential we measure an amplitude of the spectrum to be $A^{phiphi}_{rm L}=1.15pm 0.36$ (Planck $Lambda$CDM prediction corresponds to $A^{phiphi}_{rm L}=1$), and reject the no-lensing hypothesis at 5.8$sigma$, which is the highest significance achieved to date using an EB lensing estimator. Taking the cross-spectrum of the reconstructed potential with the Planck 2015 lensing map yields $A^{phiphi}_{rm L}=1.13pm 0.20$. These direct measurements of $A^{phiphi}_{rm L}$ are consistent with the $Lambda$CDM cosmology, and with that derived from the previously reported BK14 B-mode auto-spectrum ($A^{rm BB}_{rm L}=1.20pm 0.17$). We perform a series of null tests and consistency checks to show that these results are robust against systematics and are insensitive to analysis choices. These results unambiguously demonstrate that the B-modes previously reported by BICEP / Keck at intermediate angular scales ($150lesssimelllesssim 350$) are dominated by gravitational lensing. The good agreement between the lensing amplitudes obtained from the lensing reconstruction and B-mode spectrum starts to place constraints on any alternative cosmological sources of B-modes at these angular scales.
A linear polarization field on the sphere can be uniquely decomposed into an E-mode and a B-mode component. These two components are analytically defined in terms of spin-2 spherical harmonics. Maps that contain filtered modes on a partial sky can also be decomposed into E-mode and B-mode components. However, the lack of full sky information prevents orthogonally separating these components using spherical harmonics. In this paper, we present a technique for decomposing an incomplete map into E and B-mode components using E and B eigenmodes of the pixel covariance in the observed map. This method is found to orthogonally define E and B in the presence of both partial sky coverage and spatial filtering. This method has been applied to the BICEP2 and the Keck Array maps and results in reducing E to B leakage from LCDM E-modes to a level corresponding to a tensor-to-scalar ratio of $r<1times10^{-4}$.
We explore the thermal light sterile neutrino situation from cosmological perspective in the $Lambda textrm{CDM} + r_{0.05} + N_{textrm{eff}} + m^{textrm{eff}}_{textrm{s}}$ model using combinations of latest data sets available. Here, $r_{0.05}$ is the tensor-to-scalar ratio at the pivot scale of $k_*=0.05h$ Mpc$^{-1}$, $N_{textrm{eff}}$ is the effective number of relativistic species during recombination, and $m^{textrm{eff}}_{textrm{s}}$ is the effective mass of the sterile neutrino. Among Cosmic Microwave Background (CMB) datasets, we use Planck 2015 temperature and low-$l$ ($l <$ 30) polarization data and the latest data release on the B-mode polarization up to and including 2014 from the BICEP2/Keck collaboration (BK14). We also use the latest BAO data from SDSS-III BOSS DR12, MGS, and 6dFS; and a Gaussian prior (HST) on the Hubble constant ($H_0 = 73.24 pm 1.74$ km/sec/Mpc) from direct measurements. We find that inclusion of BK14 data makes the constraints on the effective mass of sterile neutrino ($m^{textrm{eff}}_{textrm{s}}$) slightly stronger by preferring higher $sigma_8$ values. The bound of $m^{textrm{eff}}_{textrm{s}} <$ 0.46 eV (95% C.L.) is found for the combination of Planck 2015, BAO and BK14 datasets, whereas the bound is $m^{textrm{eff}}_{textrm{s}} <$ 0.53 eV (95% C.L.) without the BK14 data. Our most aggressive bound of $m^{textrm{eff}}_{textrm{s}} <$ 0.28 eV (95% C.L.) is obtained with Planck 2015, HST and BK14. However, the HST prior also leads to very high $N_{textrm{eff}}$ which might be in conflict with bounds from BBN. Our analysis indicates that fully thermalized sterile neutrinos with mass $sim 1$ eV are slightly more disfavoured with the inclusion of BK14 data. It also seems to make the agreement between Planck 2015 and CFHTLenS (weak gravitational lensing data) worse due to the higher $sigma_8$ values (abstract abridged).
BICEP2 and the Keck Array are polarization-sensitive microwave telescopes that observe the cosmic microwave background (CMB) from the South Pole at degree angular scales in search of a signature of inflation imprinted as B-mode polarization in the CMB. BICEP2 was deployed in late 2009, observed for three years until the end of 2012 at 150 GHz with 512 antenna-coupled transition edge sensor bolometers, and has reported a detection of B-mode polarization on degree angular scales. The Keck Array was first deployed in late 2010 and will observe through 2016 with five receivers at several frequencies (95, 150, and 220 GHz). BICEP2 and the Keck Array share a common optical design and employ the field-proven BICEP1 strategy of using small-aperture, cold, on-axis refractive optics, providing excellent control of systematics while maintaining a large field of view. This design allows for full characterization of far-field optical performance using microwave sources on the ground. Here we describe the optical design of both instruments and report a full characterization of the optical performance and beams of BICEP2 and the Keck Array at 150 GHz.
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