[show abstract][hide abstract] ABSTRACT: Templates for polarised emission from Galactic foregrounds at frequencies
relevant to Cosmic Microwave Background (CMB) polarisation experiments are
obtained by modelling the Galactic Magnetic Field (GMF) on large scales. This
work extends the results of O'Dea et al. by including polarised synchrotron
radiation as a source of foreground emission. The polarisation direction and
fraction in this calculation are based solely on the underlying choice of GMF
model and therefore provide an independent prediction for the polarisation
signal on large scales. Templates of polarised foregrounds may be of use when
forecasting effective experimental sensitivity. In turn, as measurements of the
CMB polarisation over large fractions of the sky become routine, this model
will allow for the data to constrain parameters in the, as yet, not well
understood form of the GMF.
[show abstract][hide abstract] ABSTRACT: The upcoming generation of cosmic microwave background experiments face a major challenge in detecting the weak cosmic B-mode signature predicted as a product of primordial gravitational waves. To achieve the required sensitivity these experiments must have impressive control of systematic effects and detailed understanding of the foreground emission that will influence the signal. In this paper, we present templates of the intensity and polarization of emission from one of the main Galactic foregrounds, interstellar dust. These are produced using a model which includes a three-dimensional description of the Galactic magnetic field, examining both large and small scales. We also include in the model the details of the dust density, grain alignment and the intrinsic polarization of the emission from an individual grain. We present here Stokes parameter template maps at 150 GHz and provide an online repository () for these and additional maps at frequencies that will be targeted by upcoming experiments such as EBEX, Spider and SPTpol.
Monthly Notices of the Royal Astronomical Society 01/2012; 419:1795-1803. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Model-independent parametrisations for examining departures from General
Relativity have been increasingly studied over the past few years. Various
observables have been used to constrain the parameters and forecasts for future
surveys have been carried out. In one such forecast, galaxy cluster counts were
used to constrain the parameters. Here, we carry out a limited set of $N$-body
simulations, with a modified Poisson equation, to examine the accuracy of
existing mass functions for modified gravity cosmologies. As well as altering
the gravitational calculation, we include the effect of a screening scale to
ensure consistency of the theory with solar system tests. Our results suggest
that if a screening scale exists its effect can be taken into account in the
cluster count calculation through its effect on the linear matter power
spectrum. If this is done, the accuracy of the standard mass function formalism
in modified gravity theories with reasonably small departures from General
Relativity, as tested in this work, is comparable to the standard case.
[show abstract][hide abstract] ABSTRACT: SPIDER is a balloon-borne instrument designed to map the polarization of the cosmic microwave background (CMB) with degree-scale resolution over a large fraction of the sky. SPIDER's main goal is to measure the amplitude of primordial gravitational waves through their imprint on the polarization of the CMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve this goal, instrumental systematic errors must be controlled with unprecedented accuracy. Here, we build on previous work to use simulations of SPIDER observations to examine the impact of several systematic effects that have been characterized through testing and modeling of various instrument components. In particular, we investigate the impact of the non-ideal spectral response of the half-wave plates, coupling between focal-plane components and Earth's magnetic field, and beam mismatches and asymmetries. We also present a model of diffuse polarized foreground emission based on a three-dimensional model of the Galactic magnetic field and dust, and study the interaction of this foreground emission with our observation strategy and instrumental effects. We find that the expected level of foreground and systematic contamination is sufficiently low for SPIDER to achieve its science goals.
The Astrophysical Journal 08/2011; 738(1):63. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Model-independent parametrisations of modified gravity have attracted a lot
of attention over the past few years and numerous combinations of experiments
and observables have been suggested to constrain the parameters used in these
models. Galaxy clusters have been mentioned, but not looked at as extensively
in the literature as some other probes. Here we look at adding galaxy clusters
into the mix of observables and examine how they could improve the constraints
on the modified gravity parameters. In particular, we forecast the constraints
from combining Planck satellite Cosmic Microwave Background (CMB) measurements
and Sunyaev-Zeldovich (SZ) cluster catalogue with a DES-like weak lensing
survey. We find that cluster counts significantly improve the constraints over
those derived using CMB and WL. We then look at surveys further into the
future, to see how much better it may be feasible to make the constraints.
Journal of Cosmology and Astroparticle Physics 07/2011; 12(12). · 6.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a
divergence-free polarization pattern ("B-modes") in the Cosmic Microwave
Background (CMB). In the inflationary scenario, the amplitude of this signal is
proportional to that of the primordial scalar perturbations through the
tensor-to-scalar ratio r. We show that the expected level of systematic error
in the SPIDER instrument is significantly below the amplitude of an interesting
cosmological signal with r=0.03. We present a scanning strategy that enables us
to minimize uncertainty in the reconstruction of the Stokes parameters used to
characterize the CMB, while accessing a relatively wide range of angular
scales. Evaluating the amplitude of the polarized Galactic emission in the
SPIDER field, we conclude that the polarized emission from interstellar dust is
as bright or brighter than the cosmological signal at all SPIDER frequencies
(90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the
"Southern Hole." We show that two ~20-day flights of the SPIDER instrument can
constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when
foreground contamination is taken into account. In the absence of foregrounds,
the same limit can be reached after one 20-day flight.
Journal of Cosmology and Astroparticle Physics 06/2011; · 6.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We describe the cryogenic system for SPIDER, a balloon-borne microwave
polarimeter that will map 8% of the sky with degree-scale angular resolution.
The system consists of a 1284 L liquid helium cryostat and a 16 L
capillary-filled superfluid helium tank, which provide base operating
temperatures of 4 K and 1.5 K, respectively. Closed-cycle helium-3 adsorption
refrigerators supply sub-Kelvin cooling power to multiple focal planes, which
are housed in monochromatic telescope inserts. The main helium tank is
suspended inside the vacuum vessel with thermally insulating fiberglass
flexures, and shielded from thermal radiation by a combination of two vapor
cooled shields and multi-layer insulation. This system allows for an extremely
low instrumental background and a hold time in excess of 25 days. The total
mass of the cryogenic system, including cryogens, is approximately 1000 kg.
This enables conventional long duration balloon flights. We will discuss the
design, thermal analysis, and qualification of the cryogenic system.
[show abstract][hide abstract] ABSTRACT: We describe SPIDER, a balloon-borne instrument to map the polarization of the
millimeter-wave sky with degree angular resolution. Spider consists of six
monochromatic refracting telescopes, each illuminating a focal plane of
large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting
transition-edge sensors are distributed among three observing bands centered at
90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope
modulates the polarization of incoming light to control systematics. Spider's
first flight will be a 20-30-day Antarctic balloon campaign in December 2011.
This flight will map \sim8% of the sky to achieve unprecedented sensitivity to
the polarization signature of the gravitational wave background predicted by
inflationary cosmology. The Spider mission will also serve as a proving ground
for these detector technologies in preparation for a future satellite mission.
[show abstract][hide abstract] ABSTRACT: Here we describe the design and performance of the Spider instrument. Spider
is a balloon-borne cosmic microwave background polarization imager that will
map part of the sky at 90, 145, and 280 GHz with sub-degree resolution and high
sensitivity. This paper discusses the general design principles of the
instrument inserts, mechanical structures, optics, focal plane architecture,
thermal architecture, and magnetic shielding of the TES sensors and SQUID
multiplexer. We also describe the optical, noise, and magnetic shielding
performance of the 145 GHz prototype instrument insert.
[show abstract][hide abstract] ABSTRACT: Spider is a balloon-borne instrument designed to map the polarization of the
cosmic microwave background (CMB) with degree-scale resolution over a large
fraction of the sky. Spider's main goal is to measure the amplitude of
primordial gravitational waves through their imprint on the polarization of the
CMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve this
goal, instrumental systematic errors must be controlled with unprecedented
accuracy. Here, we build on previous work to use simulations of Spider
observations to examine the impact of several systematic effects that have been
characterized through testing and modeling of various instrument components. In
particular, we investigate the impact of the non-ideal spectral response of the
half-wave plates, coupling between focal plane components and the Earth's
magnetic field, and beam mismatches and asymmetries. We also present a model of
diffuse polarized foreground emission based on a three-dimensional model of the
Galactic magnetic field and dust, and study the interaction of this foreground
emission with our observation strategy and instrumental effects. We find that
the expected level of foreground and systematic contamination is sufficiently
low for Spider to achieve its science goals.
[show abstract][hide abstract] ABSTRACT: We examine the generation of primordial perturbations during an inflationary
epoch in generalised theories of gravity when the equations of motion are
derived using the Palatini variational principle. Both f(R) and Scalar-Tensor
theories are considered and we compare our results with those obtained under
the conventional metric formalism. Non-linear generalisations of the action
lead to different theories under the two variational choices and we obtain
distinct results for scalar and tensor spectral indices and their ratio. We
find the following general result; inflation driven solely by f(R)
modifications alone do not result in suitable curvature perturbations whilst
Scalar-Tensor theories generate nearly scalar invariant curvature perturbations
but no tensor modes.
Physical review D: Particles and fields 10/2010; 83(4).
[show abstract][hide abstract] ABSTRACT: We assess the strengths and weaknesses of several likelihood formalisms, including the XFaster likelihood. We compare the performance of the XFaster likelihood to that of the Offset Lognormal Bandpower likelihood on simulated data for the Planck satellite. Parameters estimated with these two likelihoods are in good agreement. The advantages of the XFaster likelihood can therefore be realized without compromising performance. Comment: 16 pages, 8 figures, 1 table, submitted to MNRAS
[show abstract][hide abstract] ABSTRACT: Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not limit the Spider constraints on inflation.
[show abstract][hide abstract] ABSTRACT: We develop the XFaster Cosmic Microwave Background (CMB) temperature and polarization anisotropy power spectrum and likelihood technique for the Planck CMB satellite mission. We give an overview of this estimator and its current implementation and present the results of applying this algorithm to simulated Planck data. We show that it can accurately extract the power spectrum of Planck data for the high-l multipoles range. We compare the XFaster approximation for the likelihood to other high-l likelihood approximations such as Gaussian and Offset Lognormal and a low-l pixel-based likelihood. We show that the XFaster likelihood is not only accurate at high-l, but also performs well at moderately low multipoles. We also present results for cosmological parameter Markov Chain Monte Carlo estimation with the XFaster likelihood. As long as the low-l polarization and temperature power are properly accounted for, e.g., by adding an adequate low-l likelihood ingredient, the input parameters are recovered to a high level of accuracy. Comment: 23 pages, 18 figures, submitted to MNRAS
Monthly Notices of the Royal Astronomical Society 12/2009; · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Vector perturbations sourced by topological defects can generate rotations in the lensing of background galaxies. This is a potential smoking gun for the existence of defects since rotation generates a curl-like component in the weak lensing signal which is not generated by standard density perturbations at linear order. This rotation signal is calculated as generated by cosmic strings. Future large scale weak lensing surveys should be able to detect this signal even for string tensions an order of magnitude lower than current constraints.
[show abstract][hide abstract] ABSTRACT: We introduce a new method for reconstructing the primordial power spectrum, $P(k)$, directly from observations of the Cosmic Microwave Background (CMB). We employ Singular Value Decomposition (SVD) to invert the radiation perturbation transfer function. The degeneracy of the multipole $\ell$ to wavenumber $k$ linear mapping is thus reduced. This enables the inversion to be carried out at each point along a Monte Carlo Markov Chain (MCMC) exploration of the combined $P(k)$ and cosmological parameter space. We present best--fit $P(k)$ obtained with this method along with other cosmological parameters. Comment: 23 pages, 9 figures
Journal of Cosmology and Astroparticle Physics 09/2009; · 6.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We prove that many cosmological models characterized by vectors nonminimally coupled to the curvature (such as the Turner-Widrow mechanism for the production of magnetic fields during inflation, and models of vector inflation or vector curvaton) contain ghosts. The ghosts are associated with the longitudinal vector polarization present in these models, and are found from studying the sign of the eigenvalues of the kinetic matrix for the physical perturbations. Ghosts introduce two main problems: (1) they make the theories ill-defined at the quantum level in the high energy/sub horizon regime (and create serious problems for finding a well behaved UV completion); (2) they create an instability already at the linearized level. This happens because the eigenvalue corresponding to the ghost crosses zero during the cosmological evolution. At this point the linearized equations for the perturbations become singular (we show that this happens for all the models mentioned above). We explicitly solve the equations in the simplest cases of a vector without vev in a FRW geometry, and of a vector with vev plus a cosmological constant, and we show that indeed the solutions of the linearized equations diverge when these equations become singular. Comment: 44 pages, 11 figures
[show abstract][hide abstract] ABSTRACT: The Sunyaev-Zel'dovich (SZ) effect is the inverse Compton-scattering of cosmic microwave background (CMB) photons by hot electrons in the intervening gas throughout the universe. The effect has a distinct spectral signature that allows its separation from other signals in multifrequency CMB data sets. Using CMB anisotropies measured at three frequencies by the BOOMERANG 2003 flight we constrain SZ fluctuations in the 10 arcmin to 1 deg angular range. Propagating errors and potential systematic effects through simulations, we obtain an overall upper limit of 15.3 μK (2σ) for rms SZ fluctuations in a broad bin between multipoles of 250 and 1200 at the Rayleigh-Jeans (RJ) end of the spectrum. The resulting upper limit on the local universe normalization of the density perturbations with BOOMERANG SZ data alone is σSZ 8 < 1.14 at the 95% confidence level. When combined with other CMB anisotropy and SZ measurements, we find σSZ 8 < 0.92 (95% c.l.).
The Astrophysical Journal 08/2009; 702(1):L61. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We use Minkowski Functionals (MF) to constrain a primordial non-Gaussian contribution to the CMB intensity field as observed in the 150 GHz and 145 GHz BOOMERanG maps from the 1998 and 2003 flights, respectively, performing for the first time a joint analysis of the two datasets. A perturbative expansion of the MF formulae in the limit of a weakly non-Gaussian field yields analytical formulae, derived by Hikage et al. (2006), which can be used to constrain the coupling parameter f_NL without the need for non-Gaussian simulations. We find -1020<f_NL<390 at 95% CL, significantly improving the previous constraints by De Troia et al. (2007) on the BOOMERanG 2003 dataset. These are the best f_NL limits to date for suborbital probes. Comment: 8 pages, 3 figures
[show abstract][hide abstract] ABSTRACT: How did the universe evolve? The fine angular scale (l>1000) temperature and polarization anisotropies in the CMB are a Rosetta stone for understanding the evolution of the universe. Through detailed measurements one may address everything from the physics of the birth of the universe to the history of star formation and the process by which galaxies formed. One may in addition track the evolution of the dark energy and discover the net neutrino mass. We are at the dawn of a new era in which hundreds of square degrees of sky can be mapped with arcminute resolution and sensitivities measured in microKelvin. Acquiring these data requires the use of special purpose telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and the South Pole Telescope (SPT). These new telescopes are outfitted with a new generation of custom mm-wave kilo-pixel arrays. Additional instruments are in the planning stages.