Planck Surveyor Research Articles

A Map-Making algorithm for the Planck Surveyor

We present a parallel implementation of a map-making algorithm for CMB anisotropy experiments which is both fast and efficient. We show for the first time a Maximum Likelihood, minimum variance map obtained by processing the entire data stream expected from the Planck Surveyor, under the assumption of a symmetric beam profile. Here we restrict ourselves to the case of the 30 GHz channel of the Planck Low Frequency Instrument. The extension to Planck higher frequency channels is straightforward. If the satellite pointing periodicity is good enough to average data that belong to the same sky circle, then the code runs very efficiently on workstations. The serial version of our code also runs on very competitive time-scales the map-making pipeline for current and forthcoming balloon borne experiments.

Sunyaev-Zel'dovich predictions for the Planck Surveyor satellite using the Hubble Volume simulations

ABSTRA C T We use the billion-particle Hubble Volume simulations to make statistical predictions for the distribution of galaxy clusters that will be observed by the Planck Surveyor satellite through their effect on the cosmic microwave background ‐ the Sunyaev ‐Zel’dovich (SZ) effect. We utilize the lightcone data sets for both critical density (tCDM) and flat low-density (LCDM) cosmologies: a ‘full-sky’ survey out to z , 0:5, two ‘octant’ data sets out to beyond za 1, and a 100 square degree data set extending to z , 4. Making simple, but robust, assumptions regarding both the thermodynamic state of the gas and the detection of objects against an unresolved background, we present the expected number of SZ sources as a function of redshift and angular size, and also as a function of flux (for both the thermal and kinetic effects) for three of the relevant High Frequency Instrument frequency channels. We confirm the expectation that the Planck Surveyor will detect around 5 10 4 clusters, though the exact number is sensitive to the choice of several parameters including the baryon fraction, and also to the cluster density profile, so that either cosmology may predict more clusters. We also find that the majority of detected sources should be at z , 1:5, and we estimate that around 1 per cent of clusters will be spatially resolved by the Planck Surveyor, though this has a large

Detectability of the Gravitational Lensing Effect on the Two‐Point Correlation Function of Hot Spots in Cosmic Microwave Background Maps

We present quantitative investigations of the weak-lensing effect on the two-point correlation functions of local maxima (hot spots), ξpk-pk(θ), in cosmic microwave background (CMB) maps. The lensing effect depends on the projected mass fluctuations between today and redshift zrec ≈ 1100. If we adopt the Gaussian assumption for the primordial temperature fluctuations field, the peak statistics can provide additional information about the intrinsic distribution of hot spots: that those pairs have some characteristic separation angles. The weak lensing then redistributes hot spots in the observed CMB maps from the intrinsic distribution and consequently imprints non-Gaussian signatures onto ξpk-pk(θ). In particular, since the intrinsic ξpk-pk(θ) has a pronounced depression feature around the angular scale of θ ≈ 70' for a flat universe, the weak lensing induces a large smoothing at that scale. We show that the lensing signature therefore has an advantage for effectively probing mass fluctuations with large wavelength modes around λ ≈ 50 h-1 Mpc. To reveal the detectability, we performed numerical experiments with specifications of the Microwave Anisotropy Probe (MAP) and Planck Surveyor, including the instrumental effects of beam smoothing and detector noise. We find that our method can successfully provide constraints on the amplitude of the mass fluctuations and cosmological parameters in a flat universe with and without the cosmological constant, provided that we use maps with the 65% sky coverage expected from Planck.

Fast Physical Optics Simulations of the Multi-Beam Dual-Reflector Submillimeter-Wave Telescope on the ESA PLANCK Surveyor

We present physical optics simulations of the multi-beam dual-reflector submillimeter-wave telescope on the ESA PLANCK surveyor designed for measuring the temperature anisotropies and polarization characteristics of the cosmic microwave background. The telescope is of a non-conventional Gregorian configuration, with two ellipsoidal reflectors providing a very large field of view at the focal plane where the array of 76 horn antennas feeding low-temperature detectors is located. We analyse the defocusing effects of the system, the polarization properties of the telescope, and the optical performance of the high-frequency channels based on special multi-moded horns operating at 545 and 857 GHz.

Ultra low noise and high stability receivers of planck LFI

Abstract Design concept and development of the Low Frequency Instrument (LFI) for ESA's Planck Surveyor mission is described. The LFI is a multifrequency radiometer array designed to cover the 30–100 GHz spectral range. The goal is to perform a deep, full-sky imaging of the microwave sky and to extract the wealth of cosmological information imprinted in the Cosmic Microwave Background anisotropy pattern. The LFI will survey the sky at four frequencies (30, 44, 70 and 100 GHz) with unprecedented accuracy using state-of-the-art, cryogenic, coherent receivers based on low-noise Indium Phosphide high-electron-mobility transistor amplifiers cooled at an operating temperature of 20 K. The main instrument requirements, design drivers and sources of potential systematics are discussed.

Synchrotron Emission from Hot Accretion Flows and the Cosmic Microwave Background Anisotropy

Current estimates of number counts of radio sources in the frequency range where the most sensitive Cosmic Microwave Background (CMB) experiments are carried out significantly under-represent sources with strongly inverted spectra. Hot accretion flows around supermassive black holes in the nuclei of nearby galaxies are expected to produce inverted radio spectra by thermal synchrotron emission. We calculate the temperature fluctuations and power spectra of these sources in the Planck Surveyor 30 GHz energy channel, where their emission is expected to peak. We find that their potential contribution is generally comparable to the instrumental noise, and approaches the CMB anisotropy level at small angular scales. Forthcoming CMB missions, which will provide a large statistical sample of inverted-spectra sources, will be crucial for determining the distribution of hot accretion flows in nearby quiescent galactic nuclei. Detection of these sources in different frequency channels will help constrain their spectral characteristics, hence their physical properties.

CMB anisotropy experiments

Anisotropies in the cosmic microwave background (CMB) encode information about the evolution and development of the universe. Quality observations of CMB anisotropies can provide a very strong test of cosmological models and provide high precision determination of major cosmological parameters. This paper provides a review of the COBE DMR results, the current status of the measurements of the CMB anisotropy power spectrum and then focuses current and future programs including both suborbit al observations and the two selected satellite missions: the NASA MidEX mission MAP and the ESA M3 mission Max Planck Surveyor. This review includes both a description of the experimental programs and the expected quality level of results.

Power spectrum of the Sunyaev-Zel’dovich effect

The hot gas in the IGM produces anisotropies in the cosmic microwave background (CMB) through the thermal Sunyaev-Zel'dovich (SZ) effect. The SZ effect is a powerful probe of large-scale structure in the universe, and must be carefully subtracted from measurements of the primary CMB anisotropies. We use moving-mesh hydrodynamical simulations to study the 3-dimensional statistics of the gas, and compute the mean Comptonization parameter y and the angular power spectrum of the SZ fluctuations, for different cosmologies. We compare these results with predictions using the Press-Schechter formalism. We find that the two methods agree approximately, but differ in details. We discuss this discrepancy, and show that resolution limits the reliability of our results to the $200\ensuremath{\lesssim}l\ensuremath{\lesssim}2000$ range. For cluster normalized CDM models, we find a mean y-parameter of the order of ${10}^{\ensuremath{-}6},$ one order of magnitude below the current observational limits from the COBE-FIRAS instrument. For these models, the SZ power spectrum is comparable to the primordial power spectrum around $l=2000.$ It is well below the projected noise for the upcoming MAP satellite, and should thus not be a limitation for this mission. It should be easily detectable with the future Planck Surveyor mission. We show that groups and filaments (kT\ensuremath{\lesssim}5 keV) contribute about 50% of the SZ power spectrum at $l=500.$ About half of the SZ power spectrum on these scales are produced at redshifts $z\ensuremath{\lesssim}0.1,$ and can thus be detected and removed using existing catalogs of galaxies and x-ray clusters.

Bolometers for far-infrared and submillimetre astronomy

Important scientific goals of far-infrared and submillimetre astronomy include measurements of anisotropies in the cosmic background radiation, deep imaging surveys for detection of high-red-shift galaxies, and imaging and spectroscopy of star formation regions and the interstellar medium in the milky way and nearby galaxies. Use of sensitive bolometer arrays leads to very large improvements in observing speed. Recent progress in the development of bolometric detector systems for ground-based and space-borne far-infrared and submillimetre astronomical observations is reviewed, including spider-web NTD bolometers, transition-edge superconducting sensors, and micromachined planar arrays of ion-implanted silicon bolometers. Future arrays may be based on planar absorbers without feedhorns, which offer potential advantages including more efficient use of space in the focal plane and improved instantaneous sampling of the telescope point spread function, but present challenges in suppression of stray light and RF interference. FIRST and Planck Surveyor are planned satellite missions involving passively cooled (∼70 K) telescopes, and bolometer array developments for these missions are described.

Evaluation of prototype 100 mK bolometric detector for Planck Surveyor

The High-Frequency Instrument (HFI) for the Planck Surveyor mission will measure anisotropies of the Cosmic Microwave Background (CMB) down to scales of 6 arcmin and to an accuracy of Δ T/ T=2×10 −6. Channels ranging in frequency from 100 to 857 GHz will use 100 mK spider web bolometer detectors with NTD Ge thermistors. The detectors must be photon noise limited and fast enough to preserve signal information at the 1 r.p.m. scan rate of the satellite. The prime low-frequency CMB channels at 143 and 217 GHz are the most technically demanding owing to the lower background limited NEPs. For the 143 GHz channel the requirements are that the time constant τ<5.7 ms and the NEP bol <1.53×10 −17 WHz −1/2 including contribution from amplifier noise. We present here thermal, electrical and optical data on a prototype detector which, although optimised for the 100 GHz channel, satisfies most of the requirements of the more demanding 143 GHz channel. The measurements are consistent with ideal thermal behaviour of the detector over the appropriate bias and temperature ranges for optimum performance. From optically blanked electrical measurements we determined the dependence of resistance and thermal conductance on temperature over a wide range, 70–200 mK. The optical responsivity and NEP were measured under photon background conditions similar to those expected in flight. Measurements of speed of response as a function of bias at different temperatures allowed us to determine the variation of total heat capacity with temperature. Extrapolation of these data show that in principal performance for all the Planck HFI channels can be met.

The early universe

The early Universe, at times prior to recombination 10 5.5 years after the Big Bang, can not be studied by looking at individual objects. However, there are several fossils from this epoch that can be studied. These include the abundances of light elements, and especially the Cosmic Microwave Background Radiation (CMBR). Several space missions ( Copernicus, IUE), COBE, HST) have provided information about this era, and planned missions such as the Microwave Anisotropy Probe ( MAP) and the PLANCK Surveyor will add to our knowledge. The last time when photon creation and destruction rates were fast enough to guarantee a blackbody spectrum was only a month after the Big Bang, so the lack of distortions in the spectrum of the CMBR puts limits on any processes that would add energy to the radiation field at times later than a month. The nearly perfect isotropy of the CMBR shows that the entire observable Universe had to be in causal contact prior to recombination — and this is evidence for inflation. The low amplitude anisotropies of the CMBR that do exist show “equal power on all scales” for large angular scales — more evidence for inflation — and also seem to show a preferred scale near 1°, which corresponds to acoustic oscillations in the baryon-photon fluid. Detailed studies of these acoustic oscillations by MAP and PLANCK will determine the initial conditions for the process of gravitational collapse that has produced the structures seen in the later Universe.

Large-scale structure, the cosmic microwave background and primordial non-Gaussianity

Since cosmic-microwave-background (CMB) and large-scale-structure (LSS) data will shortly improve dramatically with the Microwave Anisotropy Probe (MAP) and Planck Surveyor, and the Anglo-Australian 2-Degree Field (2dF) and Sloan Digital Sky Survey (SDSS), respectively, it is timely to ask which of the CMB or LSS will provide a better probe of primordial non-gaussianity. In this paper we consider this question, using the bispectrum as a discriminating statistic. We consider several non-gaussian models and find that in each case the CMB will provide a better probe of primordial non-gaussianity. Since the bispectrum is the lowest-order statistic expected to arise in a generic non-gaussian model, our results suggest that if CMB maps appear gaussian, then apparent deviations from gaussian initial conditions in galaxy surveys can be attributed with confidence to the effects of biasing. We demonstrate this precisely for the spatial bispectrum induced by local non-linear biasing.

Constraining isocurvature fluctuations with the Planck Surveyor

We consider the detection possibilities of isocurvature fluctuations in the future CMB satellite experiments MAP and Planck for different cosmological reference models. We present a simultaneous 10 parameter fit (8 for the case of open model) to determine the correlations between the cosmological parameters, including the isocurvature cold dark matter contribution to the anisotropy. Assuming that polarization information can be fully exploited, we find that an isocurvature perturbation can be detected by the Planck Surveyor if it contributes more than 4% to the angular power spectrum at large scales. In the absence of polarization data, the signal from isocurvature perturbations can be confused with tensor perturbations or early re-ionization effects, and the limit is larger by almost an order of magnitude.

Inhomogeneous Reionization and the Polarization of the Cosmic Microwave Background.

In a universe with inhomogeneous reionization, the ionized patches create a second-order signal in the cosmic microwave background polarization anisotropy. This signal originates in the coupling of the free-electron fluctuation to the quadruple moment of the temperature anisotropy. We examine the contribution from a simple inhomogeneous reionization model and find that the signal from such a process is below the detectable limits of the Planck Surveyor mission. However, the signal is above the fundamental uncertainty limit from cosmic variance, so that a future detection with a high-accuracy experiment on subarcminute scales is possible.

Cosmic microwave background temperature and polarization anisotropy in Brans-Dicke cosmology

We develop a formalism for calculating cosmic microwave background (CMB) temperature and polarization anisotropies in cosmological models with Brans-Dicke gravity. We then modify publicly available Boltzmann codes to calculate numerically the temperature and polarization power spectra. Results are illustrated with a few representative models. Comparing with the general-relativistic model of the same cosmological parameters, both the amplitude and the width of the acoustic peaks are different in the Brans-Dicke models. We use a covariance-matrix calculation to investigate whether the effects of Brans-Dicke gravity are degenerate with those of variation in other cosmological parameters and to simultaneously determine whether forthcoming CMB maps might be able to distinguish Brans-Dicke and general-relativistic cosmology. Although the predicted power spectra for plausible Brans-Dicke models differ from those in general relativity only slightly, we find that MAP and/or the Planck Surveyor may in principle provide a test of Brans-Dicke theory that is competitive to solar-system tests. For example, if all other parameters except for the CMB normalization are fixed, a value of the Brans-Dicke parameter ω as large as 500 could be identified (at the 2σ level) with MAP, and for Planck, values as large as ω≃3000 could be identified; these sensitivities are decreased roughly by a factor of 3 if we marginalize over the baryon density, Hubble constant, spectral index, and re-ionization optical depth. In more general scalar-tensor theories, ω may evolve with time, and in this case, the CMB probe would be complementary to that from solar-system tests.

Polarization fluctuations due to extragalactic sources

We have derived the relationship between polarization and intensity fluctuations due to point sources. In the case of a Poisson distribution of a population with uniform evolution properties and constant polarization degree, polarization fluctuations are simply equal to intensity fluctuations times the average polarization degree. Conservative estimates of the polarization degree of the classes of extragalactic sources contributing to fluctuations in the frequency ranges covered by the forthcoming space missions MAP and Planck Surveyor indicate that extragalactic sources will not be a strong limiting factor to measurements of the polarization of the Cosmic Microwave Background.

Cosmological Signature of New Parity-Violating Interactions

Are there any manifestations of parity violation other than those observed in weak interactions? A map of the cosmic microwave background (CMB) temperature and polarization will provide a new signature of $P$ violation. We examine two classes of $P$-violating interactions that would give rise to such a signature. The first interaction leads to a cosmological birefringence, possibly driven by quintessence. The other interaction leads to an asymmetry in the amplitude of right- versus left-handed gravitational waves produced during inflation. The Planck Surveyor should improve upon the current sensitivity to birefringence. While the primordial effect would most likely elude detection by MAP and Planck, it may be detectable with a future dedicated CMB polarization experiment.

The susceptibility of incoherent detector systems to cryocooler microphonics.

Mechanical cryocoolers will be used to provide 4 K cooling for the HFI bolometer instrument in the Planck Surveyor mission for measurement of the anisotropies in the cosmic microwave background. They may also find application in future Earth-observing satellites. We describe an experimental programme to investigate the effects of microphonic vibrations on infrared detectors. Our initial tests have demonstrated the feasibility of operating far-infrared photoconductive detectors in conjunction with a 4 K cryocooler for Earth observing applications. The microphonic susceptibility of a bolometer at 100 mK has also been investigated, using a modified variation of the Planck Surveyor zero gravity flight dilution system. The results of these tests gives us confidence in the proposed use of sensitive bolometers with mechanical cryocoolers for space missions. We also describe development of the bolometers, the readout systems and temperature regulators for improved systems level performance of such instruments.

The effect of point sources on satellite observations of the cosmic microwave background

We study the effect of extragalactic point sources on satellite observations of the cosmic microwave background (CMB). In order to separate the contributions resulting from different foreground components, a Fourier-space maximum-entropy method is applied to simulated observations by the Planck Surveyor satellite. In addition to point sources, the simulations include emission from the CMB and the kinetic and thermal Sunyaev-Zel'dovich effects from galaxy clusters, as well as Galactic dust, free-free and synchrotron emission. We find that the main input components are faithfully recovered and, in particular, that the quality of the CMB reconstruction is only slightly reduced by the presence of point sources. In addition, we find that it is possible to recover accurate point source catalogues at each of the Planck Surveyor observing frequencies.

Cosmic microwave background: Polarization and temperature anisotropies from symmetric structures

I consider the case of anisotropies in the Cosmic Microwave Background (CMB) from one single ordered perturbation source, or seed, existing well before decoupling between matter and radiation. Such structures could have been left by high energy symmetries breaking in the early universe. I focus on the cases of spherical and cylindrical symmetry of the seed. I give general analytic expressions for the polarization and temperature linear perturbations, factoring out of the Fourier integral the dependence on the photon propagation direction and on the geometric coordinates describing the seed. I show how the CMB perturbations manifestly reflect the symmetries of their seeds. CMB anisotropies are obtained with a line of sight integration. This treatment highlights the undulatory properties of the CMB. I show with numerical examples how the polarization and temperature perturbations propagate beyond the size of their seeds, reaching the CMB sound horizon at the time considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy from a seed intersecting the last scattering surface appears as a series of temperature and polarization waves surrounding the seed, extending on the scale of the CMB sound horizon at decoupling, roughly $1^{o}$ in the sky. Each wave is characterized by its own value of the CMB perturbation, with the same mean amplitude of the signal coming from the seed interior. These waves could allow to distinguish relics from high energy processes of the early universe from point-like astrophysical sources, because of their angular extension and amplitude. Also, the marked analogy between polarization and temperature signals offers cross correlation possibilities for the future Planck Surveyor observations.