Background:

When reducing a Cosmic Microwave Background (CMB) data set, one usually wants to produce either an estimate of the angular power spectrum C(l) or a map. Although it is the former that is utimately used to constrain cosmological parameters, there are a number of reasons why one wants to make maps as well
• It facilites comparison with other experiments;
• It facilites comparison with other foreground templates;
• It may reveal flaws in the model that are not visible in the power spectrum, such as non-Gaussian CMB features, point sources, and spatially localized systematic problems;
• We generally like to map the sky in as many frequency bands as possible.

See also:

How accurately can suborbital experiments measure the CMB?
The CMB power spectrum at l=30-200 from QMASK
Comparing and combining the Saskatoon, QMAP and COBE CMB maps
Mapping the CMB: QMAP flights
A Spin Modulated Telescope to Make Two Dimensional CMB Maps
A high-resolution map of the CMB around the NCP

Great efforts are currently being channeled into ground- and balloon-based CMB experiments, mainly to explore polarization and anisotropy on small angular scales. To optimize instrumental design and assess experimental prospects, it is important to understand in detail the atmosphere-related systematic errors that limit the science achievable with new instruments. For this purpose, we spatially compare the 648 square degree ground- and balloon-based QMASK map with the atmosphere-free WMAP map, finding beautiful agreement on all angular scales where both are sensitive. This is a reassuring quantitative assessment of the power of the state-of-the-art FFT- and matrix-based mapmaking techniques that have been used for QMASK and virtually all subsequent experiments. For the QMASK data and covariance matrix please go to the QMASK Home Page.

We measure the cosmic microwave background (CMB) power spectrum on angular scales l~30-200 (1-6 degrees) from the QMASK map, which combines the data from the QMAP and Saskatoon experiments. Since the accuracy of recent measurements leftward of the first acoustic peak is limited by sample-variance, the large area of the QMASK map (648 square degrees) allows us to place among the sharpest constraints to date in this range, in good agreement with BOOMERanG and (on the largest scales) COBE/DMR. By band-pass-filtering the QMAP and Saskatoon maps, we are able to spatially compare them scale-by-scale to check for beam- and pointing-related systematic errors. For more details please go to the QMASK Home Page.

We present a method for comparing and combining maps with different resolutions and beam shapes, and apply it to the Saskatoon, QMAP and COBE/DMR data sets. Although the Saskatoon and QMAP maps detect signal at the 21 sigma and 40 sigma levels, respectively, their difference is consistent with pure noise, placing strong limits on possible systematic errors. In particular, we obtain quantitative upper limits on relative calibration and pointing errors. Splitting the combined data by frequency shows similar consistency between the Ka- and Q-bands, placing limits on foreground contamination. The visual agreement between the maps is equally striking. Our combined QMAP+Saskatoon map, nicknamed QMASK, is publicly available at www.hep.upenn.edu/~xuyz/qmask.html together with its 6495x6495 noise covariance matrix. This thoroughly tested data set covers a large enough area (648 square degrees - currently the largest degree-scale map available) to allow a statistical comparison with COBE/DMR, showing good agreement. For more details please go to the QMASK Home Page.

We present results from the QMAP balloon experiment, which maps the Cosmic Microwave Background (CMB) and probes its angular power spectrum on degree scales. In two separate flights, data were taken in six channels at two frequency bands between 26 to 46 GHz. We describe our method for mapmaking (removal of 1/f-noise and scan-synchronous offsets) and power spectrum estimation, as well as the results of a joint analysis of the data from both flights. This produces a 527 square degree map of the CMB around the North Celestial Pole, allowing a wide variety of systematic cross-checks. The frequency dependence of the fluctuations is consistent with CMB and inconsistent with Galactic foreground emission. The anisotropy is measured in three multipole bands from l~40 to l~200, and the angular power spectrum shows a distinct rise which is consistent with the Saskatoon results. Details about this map-making process, as well as, the power spectrum extraction can be found in de Oliveira-Costa et al.(1998).

We present Cosmic Microwave Background (CMB) maps from the Santa Barbara HACME balloon experiment (Staren etal 1997), covering about 1150 square degrees split between two regions in the northern sky, near the stars gamma Ursae Minoris and alpha Leonis, respectively. The angular resolution FWHM of the beam is ~0.77 degrees in three frequency bands centered on 39, 41 and 43 GHz. The results demonstrate that the thoroughly interconnected scan strategy employed allows efficient removal of 1/f-noise. The maps display no striping, and the noise correlations are found to be virtually isotropic, decaying on an angular scale ~1 degree. The signal-to-noise ratio in the map is of order 0.5 and some individual hot and cold spots are significant at the 1 sigma-level, with many spatial features being consistent between the three channels. The results bode well for the planned follow-up experiments BEAST and ACE, since they show that even with the overly cautious assumption that 1/f-noise will be as dominant as for HACME, the problem it poses can be readily overcome with the mapmaking algorithm discussed. Details about this map-making process can be found in Tegmark et al.(1997).

Wiener filtering is a general method for estimating a signal from noise data. We made a Wiener-filtered map of the CMB fluctuations in a cap with 15 degrees of diameter, centered in the North Celestial Pole (NCP). The map was based on the 1993-1995 data from the Saskatoon experiment, with an angular resolution around 1 degree in the frequency range of 30-40 GHz. The signal-to-noise ratio in the map was the order of 2, and some individual hot and cold spots are significant at the 5 sigma level. The spatial features are found to be consistent from year to year, which reinforces the conclusion that Saskatoon results are not dominated by residual atmospheric contamination or other non-celestial signals. Details about this map-making process can be found in Tegmark et al. (1997).



The 3 first pannels show maps gerated from the subsets of data that were taken in 1993, 1994 and 1995, respectively. The 1993 data seems to be rather featureless, reflecting the fact that the 1993 data set contains considerably less information than the other 2 years of data. Similarly, the 1995 map is seen to contain more small-scale structure than the 1994 map, which reflects the fact that the angular resolution was approximately doubled in 1995. Most potencial source problems with the experiment (as underestimation of atmospheric contamination, sidelobe pickup from celestial bodies, etc) would be expect to vary in timescales much shorter than 1 year. In addition, the beam patterns were quite different in the 3 years, as described in Netterfield et al. (1996). The visual similarity between these independent maps therefore provides evidence that the bulk of the signal being detected is in fact due to temperature fluctuations on the sky rather than to unknown systematic problems.

1. "CMB Multipole Measurements in the Presence of Foregrounds" de Oliveira-Costa & Tegmark 2006, Phys. Rev. D. 74:023005.
2. "Instrument, Method, Brightness and Polarization Maps from the 2003 Flight of BOOMERanG" Masi & the BOOMERanG Collaboration 2006, ApJ, submitted.
3. "A Measurement of the Polarization-Temperature Angular Cross Power Spectrum of the CMB from the 2003 Flight of BOOMERanG" Piacentini & the BOOMERanG Collaboration 2006, ApJ, 647:833.
4. "A Measurement of the Angular Power Spectrum of the CMB Temperature Anisotropy from the 2003 Flight of BOOMERanG" Jones & the BOOMERanG Collaboration 2006, ApJ, 647:823.
5. "A Measurement of the CMB EE Spectrum from the 2003 Flight of BOOMERanG" Montroy & the BOOMERanG Collaboration 2006, ApJ, 647:813.
6. "Cosmological Parameters from the 2003 Flight of BOOMERanG" MacTavish & the BOOMERanG Collaboration 2006, ApJ, 647:799.
7. "BOOMERANG Results" Polenta & the BOOMERanG Collaboration 2005, AdSpR, 36(6):1064.
8. "How accurately can suborbital experiments measure the CMB?" de Oliveira-Costa, Tegmark, Devlin, Page, Miller, Netterfield & Xu 2005, Phys. Rev. D. 71:043004.
9. "Maps of the millimetre sky from the BOOMERanG experiment" de Bernardis & the BOOMERanG Collaboration 2003, Proceedings from "IAU Symposium 216: Maps of the Cosmos", Sydney, July 14-17.
10. "The CMB power spectrum at l=30-200 from QMASK" Xu, Tegmark & de Oliveira-Costa 2002, Phy.Rev.D 65:083002
11. "Comparing and combining the Saskatoon, QMAP and COBE CMB maps" Xu, Tegmark, de Oliveira-Costa, Devlin, Herbig, Miller, Netterfield & Page 2001, Phy.Rev.D, 63:103002.
12. "Mapping the CMB III: combined analysis of QMAP flights" de Oliveira-Costa, Devlin, Herbig, Miller, Netterfield, Page & Tegmark 1998, ApJ, 509:L77.
13. "Mapping the CMB II: the second flight of the QMAP experiment" Herbig, de Oliveira-Costa, Devlin, Miller, Netterfield, Page & Tegmark 1998, ApJ, 509:L73.
14. "Mapping the CMB I: the first flight of the QMAP experiment" Devlin, de Oliveira-Costa, Herbig, Miller, Netterfield, Page & Tegmark 1998, ApJ, 509:L69.
15. "New Techniques for Making CMB Maps" de Oliveira-Costa & Tegmark 1998, Proceedings from "Wide Field Surveys in Cosmology, 14th IAP meeting", Ed. F. Bouchet.
16. "A Spin Modulated Telescope to Make Two Dimensional CMB Maps" Staren, Meinhold, Childers, Lim, Levy, Lubin, Seiffert, Gaier, Figueiredo, Villela, Wuensche, Tegmark & de Oliveira-Costa 2000, ApJ, 539:52.
17. "Cosmic microwave background maps from the HACME experiment" Tegmark, de Oliveira-Costa, Staren, Meinhold, Lubin, Childers, Figueiredo, Gaier, Lim, Seiffert, Villela & Wuensche 2000, ApJ, 541:535.
18. "A high-resolution map of the Cosmic Microwave Background around the North Celestial Pole" Tegmark, de Oliveira-Costa, Devlin, Netterfield, Page & Wollack 1997, ApJ, 474:L77.
19. "Search for structures in the CMBR" de Oliveira-Costa & Villela 1993, Rev. Mex. Astron. Astrofis., 26:127 (Just Abstract).
20. "Structures in the CMB: hot and cold spots in the microwave sky" de Oliveira-Costa 1993, M.Sc. Thesis published by INPE, INPE-5491-TDI/508 (Avaiable under request, in Portuguese).