13,320 research outputs found
CMB Anisotropies, Large-Scale Structure and the Future
We are now beginning to learn detailed information about cosmological
parameters from the shapes of the matter and radiation power spectra, together
with their relative normalization. As more high quality data are gathered from
galaxy surveys and from microwave anisotropies, the range of allowed models is
expected to get incrementally smaller. The amount of information potentially
available from a high-resolution satellite experiment should allow a
determination of essentially {\it all} currently discussed cosmological
parameters to less than ~10%.Comment: 9 pages, including 4 figures in a uuencoded self-unpacking shell
script. To appear in Proceedings of the ASP Symposium: Clusters, Lensing and
the Future, edited by Virginia Trimbl
Using SCUBA to place upper limits on arcsecond scale CMB anisotropies at 850 microns
The SCUBA instrument on the James Clerk Maxwell Telescope has already had an
impact on cosmology by detecting relatively large numbers of dusty galaxies at
high redshift. Apart from identifying well-detected sources, such data can also
be mined for information about fainter sources and their correlations, as
revealed through low level fluctuations in SCUBA maps. As a first step in this
direction we analyse a small SCUBA data-set as if it were obtained from a
Cosmic Microwave Background (CMB) differencing experiment. This enables us to
place limits on CMB anisotropy at 850 microns. Expressed as Q_{flat}, the
quadrupole expectation value for a flat power spectrum, the limit is 152
microKelvin at 95 per cent confidence, corresponding to C_0^{1/2} < 355
microKelvin for a Gaussian autocorrelation function, with a coherence angle of
about 20--25 arcsec; These results could easily be reinterpretted in terms of
any other fluctuating sky signal. This is currently the best limit for these
scales at high frequency, and comparable to limits at similar angular scales in
the radio. Even with such a modest data-set, it is possible to put a constraint
on the slope of the SCUBA counts at the faint end, since even randomly
distributed sources would lead to fluctuations. Future analysis of sky
correlations in more extensive data-sets ought to yield detections, and hence
additional information on source counts and clustering.Comment: 12 pages, 9 postscript figures, uses mn.st
Morphing the CMB: a technique for interpolating power spectra
The confrontation of the Cosmic Microwave Background (CMB) theoretical
angular power spectrum with available data often requires the calculation of
large numbers of power spectra. The standard practice is to use a fast code to
compute the CMB power spectra over some large parameter space, in order to
estimate likelihoods and constrain these parameters. But as the dimensionality
of the space under study increases, then even with relatively fast anisotropy
codes, the computation can become prohibitive. This paper describes the
employment of a "morphing" strategy to interpolate new power spectra based on
previously calculated ones. We simply present the basic idea here, and
illustrate with a few examples; optimization of interpolation schemes will
depend on the specific application. In addition to facilitating the exploration
of large parameter spaces, this morphing technique may be helpful for Fisher
matrix calculations involving derivatives.Comment: 18 pages, including 6 figures, uses elsart.cls, accepted for
publication in New Astronomy, changes to match published versio
- …