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date	2005.03.24.11.24.19;	author PaoloPadovani;	state Exp;
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Correlation of CMB, radio/mm and optical/NIR galaxy surveys
===========================================================

The study of full-sky maps of emission in the microwave regime
provides considerable opportunities for the VO world of federated data
archives to enable the study and disentangling of various cosmological
and astrophysical effects. Whilst the Cosmic Microwave Background
anisotropy is the main scientific driver of such observations, there
is overlap and complex interplay with other branches of astronomy over
a variety of angular scales.  The large-scale emission from our own
Galaxy is an important contaminant of the CMB observations which must
be modelled and corrected to high accuracy making use of
multi-wavelength observations and inferred frequency dependencies. On
smaller scales, individual bright objects much be excised from the
maps, whilst the integrated contribution of fainter objects to the
power spectrum must be corrected for. However, emission from galaxies
and clusters of galaxies create interesting secondary anisotropies in
their own right, which can give insight into the physical nature of
the objects or universe over a range of redshifts. Below we summarise
a few more detailed examples of this interplay.

One important aspect for all of the full-sky diffuse emission survey
work, however, is the need for a common pixelisation scheme.  The
current standard in CMB science is HEALPix
(http://www.eso.org/science/healpix/).  It should also be noted that
such partitions of the sphere can also be used as indexation schemes,
which allow the fast selection of catalogued objects on the sky.

1) Integrated Sachs-Wolfe Effect

The majority of the observed CMB fluctuations originate at or near the
surface of last scattering. However, a significant contribution to
these fluctuations in those universes with either spatial curvature or
an effective cosmological constant can arise from the passage of the
CMB photons through a time-varying gravitational potential.  This
so-called integrated Sachs-Wolfe (ISW) effect is generated after the
universe ceases being matter dominated and can contribute
significantly to the CMB fluctuations on large angular scales.

Since the phases can be correlated with the matter distribution, one
may attempt to disentangle the ISW effect from other sources of CMB
anisotropy by cross-correlating the full-sky CMB emission maps with
probes which trace the large-scale matter distribution and are thus
sensitive to the evolution of the gravitational potential at late
times.  Since such effects are expected in both cosmological constant
dominated cosmologies and the so-called `quintessence' models in which
the dark-energy component itself undergoes time-variation, the change
in the magnitude of the ISW effect with redshift interval affords a
useful discriminant between these scenarios.

The two key aspects of the project relate to: i) generating a map of
the CMB sky cleaned of Galactic foreground emission and nearby point
sources; ii) the production of a homogeneous catalog of objects to
trace the large-scale gravitational potential at the moderate
redshifts at which the ISW effect imposes observable structure on the
CMB.

A good tracer of this low-redshift distribution should satisfy several
criteria:
1) the tracer objects must be numerous enough that the Poisson error
term in any cross-correlation is small
2) the tracer must probe as large a volume of redshift space as
possible, to maximise the cross-correlation signal
3) the tracer survey area should cover a large angular fraction of the
sky to minimise the "sample variance" effect due to incomplete sky
coverage in the CMB map.

Project Outline:
- combine WMAP, Planck etc CMB sky maps at various frequencies to minimise
  Galactic foreground signals OR/
  utilise surveys of Galactic emission at wavelengths where particular
  components of the emission (synchrotron, free-free, dust) are
  dominant as tracers of the foreground emission. Multiwavelength
  measurements may allow the construction of templates for subtraction
  from the CMB anisotropy data.
- from radio/IR surveys determine local sources to be removed
  from the CMB sky maps
- identify potential tracer objects of the large-scale matter
  density distribution from multi-wavelength catalogues as a
  function of redshift interval
- produce a homogeneous catalogue of tracer objects, accounting 
  for the selection functions and other catalogue specific details
  apply reconstruction methods to the tracer objects to recover 
  the underlying gravitational potential at the optimal redshift(s) 
  to probe the ISW  cross-correlate the template potential with the
  CMB sky map

VO functionality required:
o Federation of relevant datasets including interchange/merging of
  meta-data
o Identification of suitable objects and redshift intervals by
  appropriate query applications
o Generation of 2D binned object data set for cross-correlation purposes
o Visualisation of data-sets
o Statistical analysis tools to compute cross-correlation, comparison
  to theoretical models (possibly represented by an ensemble of
  simulated data-sets which must also be derived from the archives)


2) SZ Effect

The Sunyaev-Zel'dovich (SZ) effect arises from the inverse compton
scattering of photons by plasma in the hot intra-cluster medium.  The
SZ effect is in fact made up of two separate effects: One is due to
the bulk velocity of the cluster, and the other due to the thermal
velocities of the electrons in the cluster gas. These are called the
kinematic and thermal SZ effects respectively. The kinematic effect
measures the cluster peculiar velocity, whereas the thermal effect can
be used, in conjunction with images and spectra of its X-ray emission,
to study the cluster gas. The two components have different frequency
dependencies and can therefore be separated by multi-wavelength
observations. The thermal effect is null at a frequency of 210 GHz.

In the context of full-sky CMB surveys, the SZ effect can be viewed in
two ways. Firstly, as a foreground to the primary CMB anisotropies,
which must therefore be modelled and removed from the data. Secondly,
as a tracer of galaxy clusters on the sky. It is expected that the
Planck Early Compact Source Catalogue (ECSC) and Deep Early Compact
Source Survey (DECS) will contain approximately 5000 and 240 clusters
of galaxies, and indeed significant numbers of very distant
clusters. Such an unbiassed survey of the sky will provide a catalogue
of clusters to be followed-up in the optical, X-ray, and indeed by
dedicated SZ telescopes such as AMI and APEX.

These latter high sensitivity, high angular resolution instruments
will allow high-resolution imaging of the SZ effect in cluster sources
thus allowing us to understand the dynamical processes within the
cluster.  The capacity to resolve embedded sources (radio cocoons,
other point sources, lensed images of background galaxies) will
improve the understanding of the SZ measurements and their
implications for cosmology.

Project outline:

- extract candidate clusters from full-sky survey using a matched
  filter technique and frequency information
- verify sample of galaxy clusters using X-ray/optical data
- utilise optical multi-color images to derive photometric
  redshifts
- search for IR correlation and quantify galaxy evolution in clusters
- determine correlation with radio surveys to identify the 
  frequency of radio galaxies in clusters, search for radio halos
- follow-up observations with dedicated SZ telescopes for detailed
  imaging

VO functionality required:

o Federation of relevant datasets including interchange/merging of
  meta-data
o Verification of candidate cluster members by
  appropriate query applications to optical/X-ray catalogues
o Acquire multi-color information to determine phtometric
  redshifts
o Identification of candidate radio galaxy cluster members
  by querying radio catalogues with search criteria (eg. location) 
  tailored to the derived cluster sample
o Visualisation of multi-wavelength cluster data
o Deprojection algorithms to allow study of morphology in survey data
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