Max Tegmark's library: comparing

Figure 1: The number of ``sigma'' at which signal is detected in the difference map .
The null-buster test is sean to be stronger than the chi-squared-test.

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Comparing and combining CMB datasets

Author:

Max Tegmark

Abstract:

One of the best ways of finding systematic errors in CMB experiments is to compare two independent observations of the same region. We derive a set of tools for comparing and combining CMB data sets, applicable also in the common case where the two have different resolution or beam shape and therefore do not measure the same signal. We present a consistency test that is better than a chi-square test at detecting systematic errors. We show how two maps of different angular resolution can be combined without smoothing the higher resolution down to the lower one, and generalize this to arbitrary beam configurations. We also show how lossless foreground removal can be performed even for foreground models involving scale dependence, latitude dependence and spectral index variations in combination.

Reference info:

Submitted to ApJ Letters

Online references:

The methods presented in this paper are part of my CMB analysis pipeline, between the boxes for
mapmaking and power spectrum estimation. We applied several of them (both the nullbuster test and the lossless map merging) when we analyzed the QMAP experiment, described on Angelica's QMAP page. Another useful paper on how to compare CMB data sets
is that of Knox,  Bond , Jaffe, Segal  & Charbonneau  (1998).

Several of the methods described

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This page was last modified August 31, 1998.
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