Welcome to the QMASK data page

Shop here for maps and covariance matrices

Figure 1: The QMAP and Saskatoon experiments zoomed in on a bird-shaped region near the North Celestial Pole with a higher angular resolution than COBE DMR. If you want a ps file with this image, click on it.

For how the data were analyzed, please refer to the the QMASK paper (nickname for QMAP and SASKATOON) that was submitted to PRD: Xu et al. You can also get the details about QMAP experiment from three QMAP papers. You'll find additional information on the QMAP sites at Penn and Princeton and on Angelica's mapmaking page. The details about SASK experiment can be gotten by Netterfield et al . The analyzed science data sets are now public and you can download them below.

Raw maps

As described on the above-mentioned paper, the multi-gigabyte data set from both QMAP and SASK was reduced to a combined sky map. Here it is:

In the file qmask_cmbmap.dat, each row corresponds to a pixel on the sky. The five columns are x, y, z, T and sigma, where (x,y,z) is a unit vector in the direction of the pixel in equatorial coordinates (see the figure below), T is the measured temperature fluctuation and sigma is the rms noise. T and sigma are in units of micro-Kelvin. In other words, the vector x in the papers corresponds to the 4th column. You may notice that some values (noise level) in the 5th column are pretty big, or in other words, those pixels looks pretty "noisy". But they are unignorable because they are correlated noise from the deconvolution technique as described in paper so that it's important that they use the noise covariance matrix.

Noise covariance matrices

As described in the papers, the complete data product needed for a cosmological analysis is the temperature vector and the noise covariance matrix. These matrices are also public. If you want them, you can download qmask_Sigma.raw, WARNING!!!! Please click your RIGHT mouse button and then choose "Save link as...", NEVER use the left button!!!. or email xuyz@hep.upenn.edu to get an ftp directory. Here is a piece of fortran code that reads these covariance matrices and explains the format in which they are stored. The 5th column in a map file above is merely the square root of the diagonal elements in the corresponding noise covariance matrix.

Wiener-filtered maps

Since some pixels are much noisier than others and there are noise correlations between pixels, Wiener filtered maps are more useful than the raw ones for visual inspection. The images above and below are both Wiener filtered. Here they are: The pixels are in the same order as for the raw maps above. qmask_wiener.dat contains only one column, which shows the temperature (in unit micro-Kelvin) after Wiener-filtering.

Figure 2: Wiener-filtered map of the QMASK combined data. The CMB temperature is shown in coordinates where the NCP is near the center, with RA being zero at the top and increasing clockwise. If you want a clearer ps file with this image, click on it.

QMASK Power spectrum

Angular power spectrum from QMASK (l~30-200) is available now. Some points have got the smallest errorbars until April 30th, 2001 (BOOMERanG and DASI will release their new results). The figure is shown in Fig. 3, and the data are available in Xu et al
. The corresponding window functions is shown in Fig. 4.

Figure 3: Power spectrum from the QMASK combined data. If you want a clearer ps file with this image, click on it.

Figure 4: Window functions for QMASK power spectrum. The first four curves is corresponding to the four points in Fig. 3. If you want a clearer ps file with this image, click on it.

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This page was last modified Apr. 27th, 2001.
xuyz@hep.upenn.edu