CITA Research September 2002 - August 2003
Cosmology and CMB
CITA continues its long tradition of physical cosmology through the
direct interactions of theories with observations. CMB analysis has
been refined at CITA, and several of the most important data sets,
including Boomerang, CBI and Amiba have key analyses carried out at
CITA. A recent addition to the effort has been weak lensing analysis.
CITA's expertise and computing infrastructure continue to drive a
strong analysis and simulation effort, including large scale parallel
N-body and hydrodynamics.
Analysis of Cosmic Background Interferometer CMB Data
CITA researchers Dick Bond, Carlo Contaldi, and Ue-Li Pen collaborated
with former CITAzens Dmitry Pogosyan (University of Alberta), Steve
Myers (NRAO), and Simon Prunet(IAP) and with Brian Mason (NRAO) and
Tim Pearson, Tony Readhead and Jonathon Sievers of Caltech (now at
CITA) to analyze new measurements of the polarization of the CMB from
the Cosmic Background Imager experiment, a 13 element interferometer
sited on the Atacama plateau in Chile. The work involved the extension
of the analysis pipleline developed by the collaboration to include
polarization of the CMB. The CBI aims to be the first instrument to
return results on the polarization spectrum at arcminute scales. The
first results covering the analysis of the first year of polarization
measurements are expected to be released in early 2004
As part of the collaboration Dick Bond, Carlo Contaldi, and Ue-Li Pen
have also been completing the analysis of the previously collected
CBI total intensity measurements extending the analysis to two full
years of data. This work follows on from the ground breaking
results announced in May 2002 in a series of five papers by the CBI
collaboration.
Analysis of Boomerang CMB Data
The Boomerang team members at CITA, Dick Bond, Carlo Contaldi and
Barth Netterfield concluded the analysis of the 1998 flight data in a
paper where the analyzed area was extended to cover roughly 3% of the
sky. The work highlighted the robustness of the measurements and
presented the definitive picture of the power spectrum at multipoles
l<1000.
The Boomerang effort has now shifted to the analysis of the latest
flight (January 2003) which featured Polarization Sensitive Bolometers
(PSB) for the measurement of polarization of the CMB. This work is
ongoing and intense and is expected to produce a spectrum of the
polarization in early 2004. The target is to map the first acoustic
pea in the "E"-type (gradient) polarization, giving further
confirmation of the basic paradigm of perturbation generation but also
revealing the details of recombination and possible deviations from
the standard picture of anisotropy formation.
Analysis of ACBAR data
Dick Bond and Carlo contaldi, together with Dmitry Pogosyan
(University of Alberta) collaborated with the ACBAR experiment (PI
Bill Holzapfel, UC Berkeley) in the analysis of the ACBAR data. The
ACBAR team published a power spectrum with higly accurately determined
band powers in the range of multipoles between 1000 and 2500. The work
focused on extracting parameter constraints using the ACBAR spectrum
and other measurements. The results were publihsed in a paper
(Goldstein et al.) that defined the final snap-shot of the state of
the field immediately previous to the realease of the first WMAP
results. When compared to the WMAP results it highlights how
successfully and accurately the CMB experiments leading upto the WMAP
release had mapped out the basic features of the spectrum upto l=1000.
Weak Lensing Modelling and Data Analysis
This period has seen the fruition of several research frontiers.
Pen's group has entered a production stage for the weak lensing effort.
Over this year, in collaboration with students P. Zhang, T. Lu, visitor
T. Zhang, and researchers J. Dubinski, Y. Mellier, L. van Waerbeke,
which resulted in the submission of 7 new papers on weak lensing during
this period. The simulations relied on the previous generation of
HPC hardware: the CITA alphaserver GS320 and the large memory (512 GB)
Itanium cluster. This effort is now expanding into precision modelling
and analysis, which is based on a parallel efficient N-body code written
with H. Merz.
Planck mission
As part of the Canadian contribution to Planck (an European Space
Agency satellite devoted to the study of the CMB in the
sub-millimeter), CITA is developing the Quick Look Analysis (QLA)
software that will be used for the visualization and analysis of
ground calibration and in-flight data. Marc-Antoine
Miville-Deschenes, a Canadian Planck scientific associate, continued
work on the design and development of the QLA, making the link between
the instrumental and data processing teams in Europe and the
developers at CITA, and assuring that the developments at CITA follow
the needs.
Analysis of Cosmic Background Interferometer CMB Data
CITA researchers Dick Bond, Carlo Contaldi, and Ue-Li Pen collaborated
with former CITAzens Dmitry Pogosyan (University of Alberta), Steve
Myers (NRAO), and Simon Prunet(IAP) and with Brian Mason (NRAO) and
Tim Pearson, Tony Readhead and Jonathon Sievers of Caltech (now at
CITA) to analyze new measurements of the polarization of the CMB from
the Cosmic Background Imager experiment, a 13 element interferometer
sited on the Atacama plateau in Chile. The work involved the extension
of the analysis pipleline developed by the collaboration to include
polarization of the CMB. The CBI aims to be the first instrument to
return results on the polarization spectrum at arcminute scales. The
first results covering the analysis of the first year of polarization
measurements are expected to be released in early 2004.
As part of the collaboration Dick Bond, Carlo Contaldi, and Ue-Li Pen
have also been completing the analysis of the previously collected
CBI total intensity measurements extending the analysis to two full
years of data. This work follows on from the ground breaking
results announced in May 2002 in a series of five papers by the CBI
collaboration.
Analysis of Boomerang CMB Data
The Boomerang team members at CITA, Dick Bond, Carlo Contaldi and
Barth Netterfield concluded the analysis of the 1998 flight data in a
paper where the analyzed area was extended to cover roughly 3% of the
sky. The work highlighted the robustness of the measurements and
presented the definitive picture of the power spectrum at multipoles
l<1000.
The Boomerang effort has now shifted to the analysis of the latest
flight (January 2003) which featured Polarization Sensitive Bolometers
(PSB) for the measurement of polarization of the CMB. This work is
ongoing and intense and is expected to produce a spectrum of the
polarization in early 2004. The target is to map the first acoustic
pea in the "E"-type (gradient) polarization, giving further
confirmation of the basic paradigm of perturbation generation but also
revealing the details of recombination and possible deviations from
the standard picture of anisotropy formation.
Analysis of ACBAR data
Dick Bond and Carlo contaldi, together with Dmitry Pogosyan
(University of Alberta) collaborated with the ACBAR experiment (PI
Bill Holzapfel, UC Berkeley) in the analysis of the ACBAR data. The
ACBAR team published a power spectrum with higly accurately determined
band powers in the range of multipoles between 1000 and 2500. The work
focused on extracting parameter constraints using the ACBAR spectrum
and other measurements. The results were publihsed in a paper
(Goldstein et al.) that defined the final snap-shot of the state of
the field immediately previous to the realease of the first WMAP
results. When compared to the WMAP results it highlights how
successfully and accurately the CMB experiments leading upto the WMAP
release had mapped out the basic features of the spectrum upto l=1000.
Joint analysis of WMAP and weak lensing data
A collaboration between Carlo Contaldi, Henk Hoekstra and Antony Lewis
produced the first parameter estimates from a fully consistent joint
analysis of CMB and the RCS weak lensing data. The results showed how
these combinations already give constraints as good if not surpassing
those from conventional combinations such as CMB with galaxy
clustering data. As an extension of this line of research, Contaldi,
Hoekstra and Lewis are now including the final release VIRMOS data
into their pipeline in work that will be submitted shortly.
Study of low CMB power on large scales
Following the WMAP release and the confirmation of an observed
quadrupole power that is lower than expected in standard $\Lambda$CDM
models. Carlo Contaldi, Marco Peloso, Lev Kofman and Andrei Linde
(Standord University) collaborated in a paper that showed how one
could build highly tuned models of inflation to introduce a cutoff in
the initial perturbation spectrum. The cutoff scale was fit to the
WMAP data and a lower limit was obtained. Although the low quadrupole
is only marginally inconsistent with the models it has generated a
huge amount of interest in the field. Given the tuning involved in
obtaining a cutoff in the spectrum arising from inflation it is
possible that the quadrupole may be hinting at a late Universe
effect. Indeed, much of the interest has been due to the possible
connection with the late time domination by a Dark Energy component
which is responsible for the accelerating expansion rate observed by
the supernovae luminosity distance measurements, and the observed
quadrupole of the CMB. Contaldi, Peloso and Kofman are continuing the
research along these lines.
Weak lensing constraints on galaxy dark matter halos
Henk Hoekstra, Howard Yee (Toronto), and Mike Gladders (Toronto)
continued their weak lensing analysis of the imaging data from the
Red-Sequence Cluster Survey (RCS). A maximum likelihood deconvolution
of the galaxy-mass cross-correlation function allowed them to
constrain the sizes of dark matter halos around galaxies. In addition,
they were able to measure the (projected) shapes of the halos. These
measurements also provide strong constraints on alternative theories
of gravity (without dark matter): modified newtonian dynamics (MOND)
is inconsistent with these findings.
Effects of Large Scale Structure on Cluster Mass Profiles
Hoekstra continued work on the effect of distant large scale structure
on weak lensing measurements of galaxy clusters. In particular he
focussed on the constraints that can be placed on the cluster
mass profiles. Hoekstra found that the large scale structure increases
the uncertainties in the measurements by about a factor two.
Systematics in cosmic shear surveys
Hoekstra also estimated the effect of imperfections in the modeling of
the spatial variation in the PSF anisotropy on cosmic shear
measurements. He found that a good parameterisation, based on dense
star fields can significantly reduce systematics. These findings
turned out to be very relevant for the VIRMOS-DESCART survey.
Reanalysis of the VIRMOS-DESCART survey
With Ludo van Waerbeke, Hoekstra reanalysed the latter data set, which
resulted in a significant improvement over previously published
results. The new measurements appear free of systematics, which is a
major advance in this area of cosmology.
Combined weak lensing and CMB analysis
With Carlo Contaldi and Antony Lewis, Hoekstra combined CMB measurements
from WMAP with the RCS lensing results, to obtain some of the best
constraints on cosmological parameters to date.
Statistics of giant arcs
With Gladders, Yee, Hall and Barrientos, Hoekstra studies the
incidence of giant arcs around galaxy clusters. On the basis of their
data they conclude that a subset of clusters is responsible for most
of the observed lensing.
Analysis of WMAP data
Antony Lewis, with collaborators Sarah Bridle, Jochen Weller and George
Efstathiou (IoA, Cambridge) performed various analyses of the new WMAP CMB
anisotropy observations. In particular they examined the odd features on
large scales which might appear unexpected in standard cosmologies, and
performed a nearly assumption-free Monte-Carlo reconstruction of the
amplitude of the primordial perturbations as a function of scale.
Joint analysis of WMAP and weak lensing data
A collaboration between Carlo Contaldi, Henk Hoekstra and Antony Lewis
produced the first parameter estimates from a fully consistent joint
analysis of CMB and the RCS weak lensing data. The results showed how
these combinations already give constraints as good if not surpassing
those from conventional combinations such as CMB with galaxy
clustering data. As an extension of this line of research, Contaldi,
Hoekstra and Lewis are now including the final release VIRMOS data
into their pipeline in work that will be submitted shortly.
Constraints on curvaton models of inflation
Antony Lewis and Chris Gordon (DAMTP) analysed observational
constrains for various 'curvaton' models of inflation, extending
publicly available CMB codes to take account of correlations between
the various possible kinds of primordial inhomegeneities.
Extraction of B-mode signal from CMB polarization measurements
Antony Lewis generalized previous work on the extraction of "B-mode" CMB
polarization from realistically shaped observed sections of the CMB sky.
This nearly exact method should allow for robust analysis and possible
detection of primordial gravitational waves from future observations.
Primordial gravitational waves are a powerful observational probe of
different models for the early universe.
Dark energy models and the large scale CMB anisotropy
Antony Lewis and Jochen Weller (IoA, Cambridge) studied the effect of
different models of dark energy on the large scale CMB anisotropy, and gave
generalized constraints on various parameterizations using a combination of
observed data.
Survival of super-GZK photons
Together with C. Csaki (Cornell U., LNS), N. Kaloper (UC, Davis), and
J. Terning (Los Alamos), Peloso discussed a new mechanism for the survival
of super-GZK photons produced in faraway sources. The mechanism is
based on the mixing of the photons with light axions in extragalactic
magnetic fields: photons convert into axions, which are sufficiently
weakly coupled to travel large distances unimpeded; these axions then
convert back into high energy photons close to the Earth.
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