Max Tegmark's cosmology library: cobepow
You can get the 400K uncompressed
postscript file by clicking
if you are interested in
other research of mine.
The angular power spectrum of the 4 year COBE data
The angular power spectrum C_l is extracted from the 4 year
data with a 20 degree galactic cut,
using the narrowest window functions possible.
The average power in eight multipole bands is also
computed, and plotted together with a compilation
of power spectrum measurements from other experiments.
The COBE results are found to be consistent with an n=1
power spectrum with the normalization
Qrmsps=18 microkelvin reported by the COBE DMR team.
Certain non-standard cosmologies, such as "small
universe" models with nontrivial spatial topology,
predict power spectra which are not smooth functions.
Rather, they contain bumps and wiggles that may not have been
detected by other data analysis techniques such as
the Hauser-Peebles method (Wright etal 1996), the
band-power method (Hinshaw etal 1996) and
orthogonalized spherical harmonics (Gorski etal 1996),
since these methods all give broader window
functions that can smear such features out beyond recognition.
On the large angular scales probed by COBE,
the Universe thus appears to be kind to us, presenting a
power spectrum that is a simple smooth function.
Published in ApJ Letters, 464, L35 (1996)
This site also contains the latest versions of some papers that are referenced in
Tegmark 1996a ("T96"),
Tegmark & Bunn 1995,
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This page was last modified July 1, 1998.