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CMB Temperature vs Frequency
The intensity of a blackbody curve
changes rapidly with frequency.
Another way to look at the data
is to convert the measured intensity at each point
to the corresponding blackbody temperature.
If the original intensities closely follow a blackbody curve,
the corresponding temperatures
will cluster around a single value,
independent of frequency.
The plot below shows a set of precise measurements
of the temperature of the cosmic microwave background
(colored points)
compared to a perfect blackbody (horizontal black line).
Colors indicate the measurement techniques.
The data all agree with a blackbody
at temperature 2.725 K,
but the experimental uncertainties become large
at wavelengths longer than a few centimeters.
ARCADE
is a balloon-borne instrument
designed to measure the CMB spectrum
at centimeter wavelengths
(a decade below FIRAS)
to search for
new signals
that would be undetectably small
at the shorter wavelenghts measured by FIRAS.
The ARCADE frequency bands are shown in red.
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