Max Tegmark's cosmology library: sz

Figure 6. The expected 1-sigma errors of peculiar velocity measurements for the XBACs cluster sample (Ebeling 1993) for our fiducial standard cosmological model (Omega=1, h=0.5, Omega_b=0.06) and a beam size of 8' and 4', respectively. The assumed optical depths and core radii are as in Fig 5. An axisymmetric optimal filter was applied using a beta-model for the cluster gas distribution. The pixel noise is fixed and corresponds to 7 micro-Kelvin in the 4' beam.

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Martin Haehnelt & Max Tegmark


We have investigated the possibility of inferring peculiar velocities for clusters of galaxies from the Doppler shift of scattered cosmic microwave background (CMB) photons. We find that if the core radius of the gas distribution or the beam size of the instrument is larger than 3-7 arcminutes, then the maximum attainable signal-to-noise ratio is determined by confusion with primary fluctuations. For smaller angular scales, ``cosmic confusion'' is less important and instrumental noise and/or foreground emission will be the limiting factor. For a cluster with the optical depth of the Coma cluster and for an optimal filtering technique, typical one-sigma errors span the wide range from 400 to 1600 km/s, depending on the cosmological model, the resolution of the instrument and the core radius of the cluster. The results have important implications for the design of future high-resolution surveys of the CMB. Individual peculiar velocities will be measurable only for a few fast moving clusters at intermediate redshift unless cosmic fluctuations are smaller than most standard cosmological scenarios predict. However, a reliable measurement of bulk velocities of ensembles of X-ray bright clusters will be possible on very large scales (100-500 Mpc/h).

Preprint info:

Preprint MPA 883. Accepted for publication in MNRAS.

Online references:

This site also contains the latest version of another paper of mine that recurs in the text; Tegmark & Efstathiou 1995 ("T95").

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This page was last modified July 1, 1998.