CMB Foregrounds

Clustering of Extragalactic Sources from 151 MHz to 232 MHz: Clustering at 74MHz: Properties of Galactic Cirrus Clouds Observed by BOOMERanG:
    The physical properties of galactic cirrus emission are not well characterized. BOOMERanG is a balloon-borne experiment designed to study the Cosmic Microwave Background at high angular resolution in the millimeter range. The BOOMERanG 245 and 345GHz channels are sensitive to interstellar signals, in a spectral range intermediate between FIR and microwave frequencies. We look for physical characteristics of cirrus structures in a region at high galactic latitudes (b ~ -40 deg) where BOOMERanG performed its deepest integration, combining the BOOMERanG data with other available datasets at different wavelengths. We have detected eight emission patches in the 345 GHz map, consistent with cirrus dust in the Infrared Astronomical Satellite maps. The analysis technique we have developed allows to identify the location and the shape of cirrus clouds, and to extract the flux from observations with different instruments at different wavelengths and angular resolutions. We study the integrated flux emitted from these cirrus clouds using data from Infrared Astronomical Satellite (IRAS), DIRBE, BOOMERanG and Wilkinson Microwave Anisotropy Probe (WMAP) in the frequency range 23-3000 GHz (13 mm 100 micron wavelength). We fit the measured spectral energy distributions with a combination of a grey body and a power-law spectra considering two models for the thermal emission. The temperature of the thermal dust component varies in the 7 - 20 K range and its emissivity spectral index is in the 1 - 5 range. We identified a physical relation between temperature and spectral index as had been proposed in previous works. This technique can be proficiently used for the forthcoming Planck and Herschel missions data. Details can be found in Veneziani et al.(2010).
CMB multipole measurements in the presence of foregrounds:
    Most analysis of Cosmic Microwave Background spherical harmonic coefficients a_lm has focused on estimating the power spectrum C(l)=<|a_lm|^2> rather than the coefficients themselves. We present a minimum-variance method for measuring a_lm given anisotropic noise, incomplete sky coverage and foreground contamination, and apply it to the WMAP data. Our method is shown to constitute lossless data compression in the sense that the widely used quadratic estimators of the power spectrum C(l) can be computed directly from our a_lm-estimators. As the Galactic cut is increased, the error bars &Delta-a_lm on low multipoles go from being dominated by foregrounds to being dominated by sample variance from other multipoles, with the intervening minimum defining the optimal cut. Applying our method to the WMAP quadrupole and octopole, we find that their previously reported "axis of evil" alignment appears to be rather robust to Galactic cut and foreground contamination. Details can be found in de Oliveira-Costa & Tegmark (2006).
The Quest for Microwave Foreground X:
    The WMAP team has produced a foreground map that can account for most of the low-frequency Galactic microwave emission in the WMAP maps, tentatively interpreting it as synchrotron emission. Finkbeiner and collaborators have challenged these conclusions, arguing that the WMAP team "synchrotron" template is in fact not dominated by synchrotron radiation, but by some dust-related Galactic emission process, perhaps spinning dust grains, making dramatically different predictions for its behavior at lower frequencies. By cross-correlating this "synchrotron" template with 10 and 15 GHz CMB observations, we find that its spectrum turns over in a manner consistent with spinning dust emission, falling about an order of magnitude below what the synchrotron interpretation would predict. See de Oliveira-Costa et al.(2004).
The significance of the largest scale CMB fluctuations in WMAP:
    In de Oliveira-Costa et al.(2004), We investigate anomalies reported in the Cosmic Microwave Background maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large angular scales and discuss possible interpretations. Three independent anomalies involve the quadrupole and octopole:

    (1.) The cosmic quadrupole on its own is anomalous at the 1-in-20 level by being low (the cut-sky quadrupole measured by the WMAP team is more strikingly low, apparently due to a coincidence in the orientation of our Galaxy of no cosmological significance); (2.) The cosmic octopole on its own is anomalous at the 1-in-20 level by being very planar; (3.) The alignment between the quadrupole and octopole is anomalous at the 1-in-60 level.

    Although the a priori chance of all three occurring is 1 in 24000, the multitude of alternative anomalies one could have looked for dilutes the significance of such a posteriori statistics. The simplest small universe model where the universe has toroidal topology with one small dimension of order half the horizon scale, in the direction towards Virgo, could explain the three items above. However, we rule this model out using two topological tests: the S-statistic and the matched circle test.

Resolution Foreground Cleaned CMB Map from WMAP:
    We perform an independent foreground analysis of the WMAP maps to produce a cleaned CMB map (available online) useful for cross-correlation with, e.g., galaxy and X-ray maps. We use a variant of the Tegmark & Efstathiou (1996) technique that is completely blind, making no assumptions about the CMB power spectrum, the foregrounds, WMAP detector noise or external templates. Compared with the foreground-cleaned internal linear combination map produced by the WMAP team, our map has the advantage of containing less non-CMB power (from foregrounds and detector noise) outside the Galactic plane. The difference is most important on the the angular scale of the first acoustic peak and below, since our cleaned map is at the highest (13') rather than lowest (49') WMAP resolution. We also produce a Wiener filtered CMB map, representing our best guess as to what the CMB sky actually looks like, as well as CMB-free maps at the five WMAP frequencies useful for foreground studies. We argue that our CMB map is clean enough that the lowest multipoles can be measured without any galaxy cut, and obtain a quadrupole value that is slightly less low than that from the cut-sky WMAP team analysis. This can be understood from a map of the CMB quadrupole, which shows much of its power falling within the Galaxy cut region, seemingly coincidentally. Intriguingly, both the quadrupole and the octopole are seen to have power suppressed along a particular spatial axis, which lines up between the two, roughly towards (l,b) ~ (-80,60) in Virgo. Details about this analysis may be found in Tegmark et al.(2003).
The Large-Scale Polarization of the Microwave Background and Foreground:
    The DASI discovery of CMB polarization has opened a new chapter in cosmology. Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where Galactic foreground contamination is the worst, so a key challenge is to model, quantify and remove polarized foregrounds. We use the POLAR experiment, COBE/DMR and radio surveys to provide the strongest limits to date on the TE cross power spectrum of the CMB on large angular scales and to quantify the polarized synchrotron radiation, which is likely to be the most challenging polarized contaminant for the MAP satellite. We find that the synchrotron E- and B-contributions are equal to within 10% from 408-820 MHz with a hint of E-domination at higher frequencies. We quantify Faraday Rotation and Depolarization effects in the two-dimensional (l,&nu)-plane and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles. Details about this analysis may be found in de Oliveira-Costa et al.(2002).
A New Spin on Galactic Dust:
    We present a new puzzle involving Galactic microwave emission and attempt to resolve it. On one hand, a cross-correlation analysis of the WHAM H-alpha 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 with the Green Bank 140 ft telescope by Finkbeiner et al. failed to find the corresponding 8-sigma 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 100um only on large angular scales. A success for this grain segregation model is that we find the best spinning dust template to involve higher frequency maps in the range 12-60um, where emission from transiently heated small grains is important. Upcoming CMB experiments such as MAP with high resolution at low frequencies should allow a definitive test of this model. Details about this analysis may be found in de Oliveira-Costa et al.(2000)
Galactic Contamination in the QMAP Experiment:
    We quantify the level of foreground contamination in the QMAP Cosmic Microwave Background (CMB) data with two objectives: (a) measuring the level to which the QMAP power spectrum measurements need to be corrected for foregrounds and (b) using this data set to further refine current foreground models. We cross-correlate the QMAP data with a variety of foreground templates. The 30 GHz Ka-band data is found to be significantly correlated with the Haslam 408 MHz and Reich and Reich 1420 MHz synchrotron maps, but not with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and 100 microm maps or the Wisconsin H-Alpha Mapper (WHAM) survey. The 40 GHz Q-band has no significant template correlations. We discuss the constraints that this places on synchrotron, free-free and dust emission. We also reanalyze the foreground-cleaned Ka-band data and find that the two band power measurements are lowered by 2.3% and 1.3%, respectively. Details about this analysis may be found in de Oliveira-Costa et al.(1999).
Galactic Contamination in the Tenerife data:
    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 supports the spinning dust hypothesis. We also present a significant detection of synchrotron radiation at 10 GHz, useful for normalizing foreground contamination of CMB experiments at high-galactic latitudes. Details about this analysis may be found in de Oliveira-Costa et al.(1998).
Galactic emission at 19 GHz:
    We cross-correlate the 19 GHz full sky CMB survey with other maps to quantify the foreground contribution. Correlations are detected with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and 100 microm maps at high-latitudes (|b|>30 degrees), 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 COBE DMR and SK experiments and are consistent with both free-free and rotating dust grain emission. The latter provides a useful normalization of high-latitude synchrotron emission at CMB frequencies. Details about this analysis may be found in de Oliveira-Costa et al.(1998).
Removing point sources from CMB 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. Details about this analysis may be found in Tegmark & de Oliveira-Costa (1998).
Foreground emission in the Saskatoon data:
    We cross-correlated the SK Ka and Q-Band CMB data with different maps to quantify possible foreground contamination. We detected a marginal correlation (around 2 sigma) with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and 100 microm maps, but we found no significant correlation with point sources (PS), with the Haslam 408 MHz map (Has) or with the Reich and Reich 1420 MHz map (RR). 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 Kogut et al. (1996) 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. Details about this analysis may be found in de Oliveira-Costa et al.(1997).

  1. "Microwave Foregrounds" Ed. A. de Oliveira-Costa & M. Tegmark 1999 (ASP: San Francisco)

My papers on this subject:
  1. "Clustering of Extragalactic Sources from 151 MHz to 232 MHz: Implications for Cosmological 21-cm Observations" de Oliveira-Costa & Lazio 2010, submitted.
  2. "Clustering at 74MHz" de Oliveira-Costa & Capodilupo 2010, MNRAS 404:1962
  3. "Properties of Galactic Cirrus Clouds Observed by BOOMERanG" Veneziani & the BOOMERanG Collaboration 2010, ApJ 713:959
  4. "A model of diffuse Galactic radio emission from 10 MHz to 100 GHz" de Oliveira-Costa, Tegmark, Gaensler, Jonas, Landecker & Reich 2008, MNRAS 388:247
  5. "CMB Multipole Measurements in the Presence of Foregrounds" de Oliveira-Costa & Tegmark 2006, Phys. Rev. D. 74:023005.
  6. "The Quest for Microwave Foreground X" de Oliveira-Costa, Tegmark, Davies, Gutierrez, Lasenby, Rebolo & Watson 2004, ApJL 606:L89.
  7. "The Large-Scale Polarization of the Microwave Foreground" de Oliveira-Costa, Tegmark, O'Dell, Keating, Timbie, Efstathiou & Smoot 2003, Proceedings from "The Cosmic Microwave Background and its Polarization", New Astronomy Reviews, Eds. S. Hanany and K.A. Olive.
  8. "Significance of the largest scale CMB fluctuations in WMAP" de Oliveira-Costa, Tegmark, Hamilton & Zaldarriaga 2004, Phys. Rev. D., 69:3516.
  9. "A High Resolution Foreground Cleaned CMB Map from WMAP" Tegmark, de Oliveira-Costa & Hamilton 2003, Phys. Rev. D., 68:123523.
  10. "The Large-Scale Polarization of the Microwave Background and Foreground" de Oliveira-Costa, Tegmark, O'Dell, Keating, Timbie, Efstathiou & Smoot 2002, Phys. Rev. D., 68:083003.
  11. "A New Spin on Galactic Dust" de Oliveira-Costa, Tegmark, Finkbeiner, Davies, Gutierrez, Haffner, Jones, Lasenby, Reynolds, Tufte & Watson 2002, ApJ, 567:363.
  12. "Galactic Contamination in the QMAP Experiment" de Oliveira-Costa, Tegmark, Devlin, Haffner, Herbig, Miller, Page, Reynolds & Tufte 1999, ApJ, 542:L5.
  13. "CMB Satellites: Forecasts and Foregrounds" Eisenstein, Tegmark, Hu & de Oliveira-Costa 1999, Proceedings from "American Astronomical Society Meeting 194" (Just Abstract).
  14. "Overview of Foregrounds and their Impact" Tegmark, Eisenstein, Hu & de Oliveira-Costa 1999, Proceedings from "Microwave Foregrounds", Ed. A. de Oliveira-Costa & M. Tegmark.
  15. "Foregrounds and Forecasts for the CMB" Tegmark, Eisenstein, Hu & de Oliveira-Costa 1999, ApJ, 530:133.
  16. "Are we observing spinning dust grains?" de Oliveira-Costa, Tegmark, Gutierrez, Jones, Davies, Lasenby, Rebolo & Watson 1999, Proceedings from "Microwave Foregrounds", Ed. A. de Oliveira-Costa & M. Tegmark.
  17. "Cross-correlation of Tenerife data with Galactic templates - evidence for spinning dust?" de Oliveira-Costa, Tegmark, Gutierrez, Jones, Davies, Lasenby, Rebolo & Watson 1999, ApJ, 527:L9.
  18. "Galactic emission at 19 GHz" de Oliveira-Costa, Tegmark, Page & Boughn 1998, ApJ, 509:L9.
  19. "Removing point sources from CMB maps" Tegmark & de Oliveira-Costa 1998, ApJ, 500:L83.
  20. "Foreground contamination around the North Celestial Pole" de Oliveira-Costa, Kogut, Devlin, Netterfield, Page & Wollack 1997, Proceedings from "18th Texas Symposium on Relativistic Astrophysics: Texas in Chicago", Ed. A. Olinto, J. Frieman & D. Schramm.
  21. "Galactic emission at degree angular scales" de Oliveira-Costa, Kogut, Devlin, Netterfield, Page & Wollack 1997, ApJ, 482:L17.

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Last modified: Jan 4, 2014.