Influence of ion assistance on the optical properties of MgF(2).

The optical properties of MgF(2) films prepared by evaporation and ion-assisted deposition have been determined from transmittance and near-normal incidence reflectance measurements and also from electron-energy loss spectroscopy (EELS). The results show that oxygen-ion assistance leads to higher extinction coefficients for wavelengths <180 nm. Transmission electron microscopy studies show that the crystal grain size of MgF(2) films is not strongly affected by oxygen or argon-ion bombardment. The presence of MgO in the films is inferred from RBS measurements and proposed to be the major factor influencing VUV losses. EELS is also demonstrated to be a valuable technique for determination of optical properties from the near-infrared to x-ray regions of the spectrum

The Atacama Cosmology Telescope: Calibration with WMAP Using Cross-Correlations

We present a new calibration method based on cross-correlations with WMAP and apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing strategy and map making procedure allows an unbiased reconstruction of the modes in the maps over a wide range of multipoles. By directly matching the ACT maps to WMAP observations in the multipole range of 400 < ell < 1000, we determine the absolute calibration with an uncertainty of 2% in temperature. The precise measurement of the calibration error directly impacts the uncertainties in the cosmological parameters estimated from the ACT power spectra. We also present a combined map based on ACT and WMAP data that has high signal-to-noise over a wide range of multipoles

THE ATACAMA COSMOLOGY TELESCOPE: A MEASUREMENT OF THE 600 < l < 8000 COSMIC MICROWAVE BACKGROUND POWER SPECTRUM AT 148 GHz

We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz. The measurement uses maps with 1′.4 angular resolution made with data from the Atacama Cosmology Telescope (ACT). The observations cover 228 deg2 of the southern sky, in a 4°.2 wide strip centered on declination 53° south. The CMB at arcminute angular scales is particularly sensitive to the Silk damping scale, to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by radio sources and dusty galaxies. After masking the 108 brightest point sources in our maps, we estimate the power spectrum between 600 < ℓ < 8000 using the adaptive multi-taper method to minimize spectral leakage and maximize use of the full data set. Our absolute calibration is based on observations of Uranus. To verify the calibration and test the fidelity of our map at large angular scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP power spectrum from 250 < ℓ < 1150. The power beyond the Silk damping tail of the CMB (ℓ ∼ 5000) is consistent with models of the emission from point sources. We quantify the contribution of SZ clusters to the power spectrum by fitting to a model normalized to σ 8 = 0.8. We constrain the model's amplitude ASZ < 1.63 (95% CL). If interpreted as a measurement of σ 8, this implies σ 8SZ < 0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly to a six-parameter ACDM model plus point sources and the SZ effect is consistent with these results. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A

The Atacama Cosmology Telescope: cosmological parameters from three seasons of data

We present constraints on cosmological and astrophysical parameters from high-resolution microwave background maps at 148 GHz and 218 GHz made by the Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to 2010. A model of primary cosmological and secondary foreground parameters is fit to the map power spectra and lensing deflection power spectrum, including contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy from unresolved infrared sources, radio sources, and the correlation between the tSZ effect and infrared sources. The power ℓ2Cℓ/2π of the thermal SZ power spectrum at 148 GHz is measured to be 3.4±1.4 μK2 at ℓ = 3000, while the corresponding amplitude of the kinematic SZ power spectrum has a 95% confidence level upper limit of 8.6 μK2. Combining ACT power spectra with the WMAP 7-year temperature and polarization power spectra, we find excellent consistency with the LCDM model. We constrain the number of effective relativistic degrees of freedom in the early universe to be Neff = 2.79±0.56, in agreement with the canonical value of Neff = 3.046 for three massless neutrinos. We constrain the sum of the neutrino masses to be Σmν < 0.39 eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and Hubble constant measurements. We constrain the amount of primordial helium to be Yp = 0.225±0.034, and measure no variation in the fine structure constant α since recombination, with α/α0 = 1.004±0.005. We also find no evidence for any running of the scalar spectral index, dns/dln k = -0.004±0.012. © 2013 IOP Publishing Ltd and Sissa Medialab srl

The Atacama Cosmology Telescope: cosmological parameters from three seasons of data

We present constraints on cosmological and astrophysical parameters from high-resolution microwave background maps at 148 GHz and 218 GHz made by the Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to 2010. A model of primary cosmological and secondary foreground parameters is fit to the map power spectra and lensing deflection power spectrum, including contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy from unresolved infrared sources, radio sources, and the correlation between the tSZ effect and infrared sources. The power ℓ2Cℓ/2π of the thermal SZ power spectrum at 148 GHz is measured to be 3.4±1.4 μK2 at ℓ = 3000, while the corresponding amplitude of the kinematic SZ power spectrum has a 95% confidence level upper limit of 8.6 μK2. Combining ACT power spectra with the WMAP 7-year temperature and polarization power spectra, we find excellent consistency with the LCDM model. We constrain the number of effective relativistic degrees of freedom in the early universe to be Neff = 2.79±0.56, in agreement with the canonical value of Neff = 3.046 for three massless neutrinos. We constrain the sum of the neutrino masses to be Σmν &lt; 0.39 eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and Hubble constant measurements. We constrain the amount of primordial helium to be Yp = 0.225±0.034, and measure no variation in the fine structure constant α since recombination, with α/α0 = 1.004±0.005. We also find no evidence for any running of the scalar spectral index, dns/dln k = -0.004±0.012. © 2013 IOP Publishing Ltd and Sissa Medialab srl