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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file with the paper. Click
if you are interested in other research of mine.
Comparing and combining CMB datasets
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.
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Submitted to ApJ Letters
The methods presented in this paper are part of my CMB analysis
, 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
. Another useful paper on how to compare CMB data
is that of Knox,
Bond , Jaffe, Segal & Charbonneau (1998)
Several of the methods described
This page was last modified August 31, 1998.