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Index - ... - Associated Weak Lensing Survey - Sunyaev-Zel'Dovich Survey - Consortium Publications - ...
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The thermal SZ effect signal from a cluster is given by
TRJ
-45
(LX/1037 W)1/2
(Te/keV)3/4
K
K and
500 K,
respectively, and will have angular sizes > 30".
Two types of SZ effect observation of the XMM LSS survey field will be
made. We will map the LX > 1038 W clusters,
initially using the OCRA-p receiver currently being developed for the Torun
32-m telescope. This instrument, and its upgrade, OCRA-f, which will be
available 1 year later, will be able to detect SZ effects of
100 K on arcminute scales in a
few hours of observing. Although confusion by the radio source environment
of the cluster will limit the accuracy of the OCRA measurements on their
own, we will also make VLA high-frequency maps of the clusters, and these
will allow good radio source corrections. Additional SZ effect observations,
with AMiBA, will be made during AMiBA's commissioning phase, and
observations with other SZ-capable instruments (such as SCUBA and CARMA)
will be sought for clusters of particular interest. Such observations should
provide 10-20 arcsec scale maps which would be interpreted on an individual
basis in comparison with the X-ray images of the clusters.
These observations will measure cluster SZ effects
which can be combined with the integrated XMM fluxes and models of
cluster atmospheres (with some parameters fitted to the XMM
structures) to produce a Hubble diagram with 23 points at redshifts to
greater than 1. This should be sufficient to provide a measurement
of the Hubble constant to about 5 per cent accuracy, and would easily
show the curvature implied by the recent supernova results which
suggest an accelerating Universe. Detailed structural studies of these
clusters in the X-ray and SZ effects, combined with optical images (to
provide weak shear maps), will measure how the baryonic mass fraction
in clusters varies as a function of z, a measurement that is of
fundamental importance for assessing the manner in which clusters are
formed.
On a longer timescale, the entire LSS field will be surveyed by OCRA,
providing a blind SZ effect survey with a resolution of about
1 arcmin and a sensitivity of
100 K, and by the Planck
satellite, which will provide a blind SZ effect survey with a resolution of
5 arcmin and a sensitivity of 25 K.
While with Planck the beam dilution of the highest-redshift clusters in the
XMM survey is severe, OCRA's higher angular resolution is well matched to
the angular sizes of clusters to z > 2. With the combined surveys
we should easily detect clusters with central SZ effects
> 200 K at z > 1.
Objects not detected by XMM but appearing in the microwave background
surveys would be cool, baryon-rich, clusters (or unusually extended,
low-surface brightness clusters): a combined blind X-ray/microwave
background survey is the best way to discover such objects if they exist.
For low-redshift clusters, Planck's beam dilution is less severe but OCRA's
beam-switching leads to reduced efficiency, we will detect all clusters
with X-ray luminosities above about 3 1036 W and
z < 0.5. This will allow us to build up a baryonic audit of
clusters of galaxies, to be compared with the nucleosynthesis results, and
hence to provide further clues about the location of unseen matter in the
Universe.
The time-scales of the observations:
| OCRA-p | start mid-2002, high-sensitivity pointed observations winter 2002 |
| OCRA-f | (improved version of OCRA-p), start high-sensitivity mapping in winter 2004 (at latest) |
| Planck | 2008 first data available |
| AMiBA | Expect trial mapping with full system in 2004. Good SZ mapping should follow quickly. |
| SCUBA | Observations are possible whenever we have a source list that can be relied on. We just have to propose for the time. |