Angelica de Oliveira-Costa

Foregrounds and Forecasts for the Cosmic Microwave Background

One of the main challenges facing upcoming cosmic microwave background (CMB) experiments will be to distinguish the cosmological signal from foreground contamination. We present a comprehensive treatment of this problem and study how foregrounds degrade the accuracy with which the Boomerang, MAP, and Planck experiments can measure cosmological parameters. Our foreground model includes not only the normalization, frequency dependence, and scale dependence for each physical component, but also variations in frequency dependence across the sky. When estimating how accurately cosmo- logical parameters can be measured, we include the important complication that foreground model parameters (we use about 500) must be simultaneously measured from the data as well. Our results are quite encouraging: despite all these complications, precision measurements of most cosmological param- eters are degraded by less than a factor of 2 for our main foreground model and by less than a factor of 5 in our most pessimistic scenario. Parameters measured though large-angle polarization signals suUer more degradation: up to 5 in the main model and 25 in the pessimistic case. The foregrounds that are potentially most damaging and therefore most in need of further study are vibrating dust emission and point sources, especially those in the radio frequencies. It is well known that E and B polarization contain valuable information about reionization and gravity waves, respectively. However, the cross- correlation between polarized and unpolarized foregrounds also deserves further study, as we —nd that it carries the bulk of the polarization information about most other cosmological parameters. Subject headings: cosmic microwave backgrounddiUuse radiationmethods: numerical ¨ polarization

A model of diffuse Galactic radio emission from 10 MHz to 100 GHz

Understanding diffuse Galactic radio emission is interesting both in its own right and for minimizing foreground contamination of cosmological measurements. cosmic microwave background experiments have focused on frequencies ≥ 10 GHz, whereas 21-cm tomography of the high-redshift universe will mainly focus on ≤0.2 GHz, for which less is currently known about Galactic emission. Motivated by this, we present a global sky model derived from all publicly available total power large-area radio surveys, digitized with optical character recognition when necessary and compiled into a uniform format, as well as the new Villa Elisa data extending the 1.42-GHz map to the entire sky. We quantify statistical and systematic uncertainties in these surveys by comparing them with various global multifrequency model fits. We find that a principal component based model with only three components can fit the 11 most accurate data sets (at 10, 22, 45 and 408 MHz and 1.42, 2.326, 23, 33, 41, 61, 94 GHz) to an accuracy around 1-10 per cent depending on frequency and sky region. Both our data compilation and our software returning a predicted all-sky map at any frequency from 10 MHz to 100 GHz are publicly available at http://space.mit.edu/home/angelica/gsm.

Galactic Microwave Emission at Degree Angular Scales

We cross-correlate the Saskatoon Ka- and Q-band cosmic microwave background (CMB) data with different maps to quantify possible foreground contamination. We detect a marginal correlation (2 σ) with the Diffuse Infrared Background Experiment (DIRBE) 240, 140, and 100 μm maps, but we find no significant correlation with point sources, with the Haslam 408 MHz map, or with the Reich and Reich 1420 MHz map. The rms amplitude of the component correlated with DIRBE is about 20% of the CMB signal. Interpreting this component as free-free emission, this normalization agrees with that of the 1996 works of Kogut et al. and supports the hypothesis that the spatial correlation between dust and warm ionized gas observed on large angular scales persists to smaller angular scales. Subtracting this contribution from the CMB data reduces the normalization of the Saskatoon power spectrum by only a few percent.

Removing Point Sources from Cosmic Microwave Background Maps

For high-precision cosmic microwave background (CMB) experiments, contamination from extragalactic point sources is a major concern. It is therefore useful to be able to detect and discard point source contaminated pixels using the map itself. We show that the sensitivity with which this can be done can often be greatly improved (by factors between 2.5 and 18 for the upcoming Planck mission) by a customized hi-pass filtering that suppresses fluctuations due to CMB and diffuse galactic foregrounds. This means that point source contamination will not severely degrade the cleanest Planck channels unless current source count estimates are off by more than an order of magnitude. A catalog of around 40,000 far infra-red sources at 857 GHz may be a useful by-product of Planck.For high-precision cosmic microwave background (CMB) experiments, contamination from extragalactic point sources is a major concern. It is therefore useful to be able to detect and discard point-source-contaminated pixels using the map itself. We show that the sensitivity with which this can be done can often be greatly improved (by factors between 2.5 and 18 for the upcoming Planck mission) by a customized high-pass filtering that suppresses fluctuations due to the CMB and diffuse galactic foregrounds. This means that point-source contamination will not severely degrade the cleanest Planck channels unless current source count estimates are off by an order of magnitude. A catalog of around 40,000 sources at 857 GHz may be a useful by-product of Planck.

Cross-Correlation of Tenerife Data with Galactic Templates-Evidence for Spinning Dust?

The recent discovery of dust-correlated diffuse microwave emission has prompted two rival explanations: free-free emission and spinning dust grains. We present new detections of this component at 10 and 15 GHz by the switched-beam Tenerife experiment. The data show a turnover in the spectrum and thereby support the spinning dust hypothesis. We also present a significant detection of synchrotron radiation at 10 GHz, which is useful for normalizing foreground contamination of cosmic microwave background experiments at high galactic latitudes.

How to measure CMB polarization power spectra without losing information

We present a method for measuring CMB polarization power spectra given incomplete sky coverage and test it with simulated examples such as Boomerang 2001 and MAP. By augmenting the quadratic estimator method with an additional step, we find that the E and B power spectra can be effectively disentangled on angular scales substantially smaller than the width of the sky patch in the narrowest direction. We find that the basic quadratic and maximum-likelihood methods display an unneccesary sensitivity to systematic errors when

A NEW SPIN ON GALACTIC DUST

T\ensuremath{-}E

Galactic Emission at 19 GHz

cross-correlation is involved, and show how this problem can be eliminated at negligible cost in increased error bars. We also test numerically the widely used approximation that sample variance scales inversely with sky coverage, and find it to be an excellent approximation on scales substantially smaller than the sky patch.

Mapping the Cosmic Microwave Background Anisotropy:Combined Analysis of QMAP Flights

We present a new puzzle involving Galactic microwave emission and attempt to resolve it. On one hand, a cross-correlation analysis of the Wisconsin Hα Mapper map with the Tenerife 10 and 15 GHz maps shows that the well-known DIRBE correlated microwave emission cannot be dominated by free-free emission. On the other hand, recent high-resolution observations in the 8-10 GHz range with the Green Bank 140 foot telescope by Finkbeiner et al. failed to find the corresponding 8 σ signal that would be expected in the simplest spinning-dust models. So what physical mechanism is causing this ubiquitous dust-correlated emission? We argue for a model predicting that spinning dust is the culprit after all, but that the corresponding small grains are well correlated with the larger grains seen at 100 μm only on large angular scales. In support of this grain-segregation model, we find that the best spinning-dust template involves higher frequency maps in the range 12-60 μm, in which emission from transiently heated small grains is important. Upcoming cosmic microwave background experiments such as ground-based interferometers, the Microwave Anisotropy Probe, and the Planck low-frequency interferometer with high resolution at low frequencies should allow a definitive test of this model.

A Limit on the Large Angular Scale Polarization of the Cosmic Microwave Background

We cross-correlate a 19 GHz full sky cosmic microwave background survey with other maps to quantify the foreground contribution. Correlations are detected with the DIRBE 240, 140, and 100 μm maps at high latitudes (|b| > 30°), and marginal correlations are detected with the Haslam 408 MHz and the Reich & Reich 1420 MHz synchrotron maps. The former agree well with extrapolations from higher frequencies probed by the COBE Differential Microwave Radiometer and Saskatoon experiments and are consistent with both free-free and rotating dust grain emission.