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This paper discusses the science case for a sensitive spectro-polarimetric survey of the microwave sky. Such a survey would provide a tomographic and dynamic census of the three-dimensional distribution of hot gas, velocity flows, early metals, dust, and mass distribution in the entire Hubble volume, exploit CMB temperature and polarisation anisotropies down to fundamental limits, and track energy injection and absorption into the radiation background across cosmic times by measuring spectral distortions of the CMB blackbody emission. In addition to its exceptional capability for cosmology and fundamental physics, such a survey would provide an unprecedented view of microwave emissions at sub-arcminute to few-arcminute angular resolution in hundreds of frequency channels, a data set that would be of immense legacy value for many branches of astrophysics. We propose that this survey be carried out with a large space mission featuring a broad-band polarised imager and a moderate resolution spectro-imager at the focus of a 3.5 m aperture telescope actively cooled to about 8K, complemented with absolutely-calibrated Fourier Transform Spectrometer modules observing at degree-scale angular resolution in the 10–2000 GHz frequency range. We propose two observing modes: a survey mode to map the entire sky as well as a few selected wide fields, and an observatory mode for deeper observations of regions of specific interest.

We present a Bayesian inference method to characterize the dust emission properties using the well-known dust- |${\rm H\,{\small I}}$| correlation in the diffuse interstellar medium at Planck frequencies |$\nu \ge 217$|  GHz. We use the Galactic |${\rm H\,{\small I}}$| map from the Galactic All-Sky Survey (GASS) as a template to trace the Galactic dust emission. We jointly infer the pixel-dependent dust emissivity and the zero level present in the Planck intensity maps. We use the Hamiltonian Monte Carlo technique to sample the high-dimensional parameter space (⁠|$D \sim 10^3$|⁠). We demonstrate that the methodology leads to unbiased recovery of dust emissivity per pixel and the zero level when applied to realistic Planck sky simulations over a 6300  |$\rm {deg}^2$| area around the Southern Galactic pole. As an application on data, we analyse the Planck intensity map at 353 GHz to jointly infer the pixel-dependent dust emissivity at |$N_{\rm side}=32$| resolution (1.8° pixel size) and the global offset. We find that the spatially varying dust emissivity has a mean of 0.031 MJy sr |$^{-1}$| |$(10^{20} \, \mathrm{cm^{-2}})^{-1}$| and |$1\sigma$| standard deviation of 0.007 MJy sr |$^{-1}$| |$(10^{20} \, \mathrm{cm^{-2}})^{-1}$|⁠. The mean dust emissivity increases monotonically with increasing mean |${\rm H\,{\small I}}$| column density. We find that the inferred global offset is consistent with the expected level of cosmic infrared background (CIB) monopole added to the Planck data at 353 GHz. This method is useful in studying the line-of-sight variations of dust spectral energy distribution in the multiphase interstellar medium. [ABSTRACT FROM AUTHOR]

Exploring Cosmic History and Origin (ECHO), popularly known as 'CMB-Bh |$\overline{a}$| rat', is a space mission that has been proposed to the Indian Space Research Organisation for the scientific exploitation of the cosmic microwave background (CMB) at the next level of precision and accuracy. The quest for the CMB polarization B-mode signals, generated by inflationary gravitational waves in the very early universe, is one of the key scientific goals of its experimental design. This work studies the potential of the proposed ECHO instrumental configuration to detect the target tensor-to-scalar ratio r ∼ 10−3 at 3σ significance level, which covers the predictions of a large class of inflationary models. We investigate the performance of two different component separation pipelines, |${\mathtt {NILC}}$| and |${\mathtt {Commander}}$|⁠ , for the measurement of r in the presence of different physically motivated models of astrophysical foregrounds. For a simplistic foreground model (only polarized dust and synchrotron), both component separation pipelines can achieve the desired sensitivity of ECHO , i.e. σ(r  = 0) ∼ (0.4–0.7) × 10−3. |${\mathtt {NILC}}$| performs better than |${\mathtt {Commander}}$| in terms of bias on recovered r for complex spectral models (power law and curved power law) of the synchrotron emission and complex dust models (dust decorrelation). Assuming 84 per cent delensing, we can achieve an improvement of σ(r  = 0) by approximately 50 per cent as compared to the results obtained for the same configuration without any lensing correction. [ABSTRACT FROM AUTHOR]

Many scientists from India have been working in the area of gravitaional wave detection as part of the LIGO international collaboration. This article recounts how these smaller scale efforts grew into a proposal for locating an advanced detector in India, which brings very significant scientific advantages. There is now in-principle approval for funding the Indian contribution to building such a facility. The article brings out the opportunities as well as major challenges which now open up to a much wider community of young scientists and engineers, in building and running such a unique laboratory. [ABSTRACT FROM AUTHOR]

A stochastic gravitational wave background (SGWB) would gravitationally lens the cosmic microwave background (CMB) photons. We correct the results provided in existing literature for modifications to the CMB polarization power spectra due to lensing by gravitational waves. Weak lensing by gravitational waves distorts all four CMB power spectra; however, its effect is most striking in the mixing of power between the E mode and B mode of CMB polarization. This suggests the possibility of using measurements of the CMB angular power spectra to constrain the energy density (OGW) of the SGWB. Using current data sets (QUAD, WMAP, and ACT), we find that the most stringent constraints on the present OGW come from measurements of the angular power spectra of CMB temperature anisotropies. In the near future, more stringent bounds on OGW can be expected with improved upper limits on the B modes of CMB polarization. Any detection of B modes of CMB polarization above the expected signal from large scale structure lensing could be a signal for a SGWB. [ABSTRACT FROM AUTHOR]

Using a nonparametric function estimation methodology, we present a comparative analysis of the Wilkinson Microwave Anisotropy Probe (WMAP) 1-, 3-, 5-, and 7-year data releases for the cosmic microwave background (CMB) angular power spectrum with respect to the following key questions. (1) How well is the power spectrum determined by the data alone? (2) How well is the ACDM model supported by a model-independent, data-driven analysis? (3) What are the realistic uncertainties on peak/dip locations and heights? Our results show that the height of the power spectrum is well determined by data alone for multipole l approximately less than 546 (1-year), 667 (3-year), 804 (5-year), and 842 (7-year data). We show that parametric fits based on the ACDM model are remarkably close to our nonparametric fits in l-regions where data are sufficiently precise. In contrast, the power spectrum for an HACDM model is progressively pushed away from our nonparametric fit as data quality improves with successive data realizations, suggesting incompatibility of this particular cosmological model with respect to the WMAP data sets. We present uncertainties on peak/dip locations and heights at the 95% (2σ) level of confidence and show how these uncertainties translate into hyperbolic "bands" on the acoustic scale (lA) and peak shift (Φm) parameters. Based on the confidence set for the 7-year data, we argue that the low-l upturn in the CMB power spectrum cannot be ruled out at any confidence level in excess of about 10% (≈0. 12σ). Additional outcomes of this work are a numerical formulation for minimization of a noise-weighted risk function subject to monotonicity constraints, a prescription for obtaining nonparametric fits that are closer to cosmological expectations on smoothness, and a method for sampling cosmologically meaningful power spectrum variations from the confidence set of a nonparametric fit. [ABSTRACT FROM AUTHOR]

The observables of the perturbed universe, cosmic microwave background (CMB) anisotropy and large structures depend on a set of cosmological parameters, as well as the assumed nature of primordial perturbations. In particular, the shape of the primordial power spectrum (PPS) is, at best, a well-motivated assumption. It is known that the assumed functional form of the PPS in cosmological parameter estimation can affect the best-fit-parameters and their relative confidence limits. In this paper, we demonstrate that a specific assumed form actually drives the best-fit parameters into distinct basins of likelihood in the space of cosmological parameters where the likelihood resists improvement via modifications to the PPS. The regions where considerably better likelihoods are obtained allowing free-form PPS lie outside these basins. In the absence of a preferred model of inflation, this raises a concern that current cosmological parameter estimates are strongly prejudiced by the assumed form of PPS. Our results strongly motivate approaches toward simultaneous estimation of the cosmological parameters and the shape of the primordial spectrum from upcoming cosmological data. It is equally important for theorists to keep an open mind towards early universe scenarios that produce features in the PPS. [ABSTRACT FROM AUTHOR]

This paper provides full sky maps of foreground emission in all Wilkinson Microwave Anisotropy Probe ( WMAP) channels, with very low residual contamination from the cosmic microwave background (CMB) anisotropies and controlled level of instrumental noise. Foreground maps are obtained by subtraction of a properly filtered CMB map, obtained from linear combinations of needlet-based representations of all WMAP observations and of a map. The error in the reconstructed foreground maps on large scales is significantly lower than the original error due to CMB contamination, while remaining of the order of the original WMAP noise on small scales. The level of the noise is estimated, which permits to implement local filters for maximizing the local signal-to-noise ratio. An example of such filtering, which reduces the small-scale noise using latitude-dependent filters, is implemented. This enhances significantly the contrast of galactic emission, in particular on intermediate angular scales and at intermediate galactic latitude. The clean WMAP foreground maps can be used to study the galactic interstellar medium, in particular for the highest frequency channels for which the proper subtraction of CMB contamination is mandatory. The foregrounds maps can be downloaded from a dedicated website. [ABSTRACT FROM AUTHOR]

The Universe is the grandest conceivable scale on which the human mind can strive to understand nature. The amazing aspect of cosmology, the branch of science that attempts to understand the origin and evolution of the Universe, is that it is largely comprehensible by applying the same basic laws of physics that we use for other branches of physics. The observed cosmic microwave background (CMB) is understood by applying the basic laws of radiative processes and transfer, masterfully covered in the classic text by S. Chandrasekhar, in the cosmological context. In addition to the now widely acclaimed temperature anisotropy, there is also linear polarization information imprinted on the observed Cosmic Microwave background. CMB polarization already has addressed, and promises to do a lot more to unravel the deepest fundamental queries about physics operating close to the origin of the Universe. [ABSTRACT FROM AUTHOR]

Filaments are one of the most prominent features visible in the galaxy distribution. Considering the luminous red galaxies in the Sloan Digital Sky Survey Data Release Seven (SDSS DR7), we have analysed the filamentarity in 11 nearly 2D sections through a volume limited subsample of these data. The galaxy distribution, we find, has excess filamentarity in comparison to a random distribution of points. We use a statistical technique 'Shuffle' to determine L, the largest length-scale at which we have statistically significant filaments. We find that L varies in the range across the 11 slices, with a mean value . Longer filaments, though possibly present in our data, are not statistically significant and are the outcome of chance alignments. [ABSTRACT FROM AUTHOR]

Over the last decade, measurements of the cosmic microwave background (CMB) anisotropy have spearheaded the remarkable transition of cosmology into a precision science. However, addressing the systematic effects in the increasingly sensitive, high-resolution, ‘full’ sky measurements from different CMB experiments poses a stiff challenge. The analysis techniques must not only be computationally fast to contend with the huge size of the data, but the higher sensitivity also limits the simplifying assumptions which can then be invoked to achieve the desired speed without compromising the final precision goals. While maximum likelihood is desirable, the enormous computational cost makes the suboptimal method of power spectrum estimation using pseudo-C l unavoidable for high-resolution data. The debiasing of the pseudo-C l needs account for non-circular beams, together with non-uniform sky coverage. We provide a (semi)analytic framework to estimate bias in the power spectrum due to the effect of beam non-circularity and non-uniform sky coverage, including incomplete/masked sky maps and scan strategy. The approach is perturbative in the distortion of the beam from non-circularity, allowing for rapid computations when the beam is mildly non-circular. We advocate that it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transform die down fast with m. We numerically implement our method for non-rotating beams. We present preliminary estimates of the computational cost to evaluate the bias for the upcoming CMB anisotropy probes , with angular resolution comparable to the Planck surveyor mission. We further show that this implementation and estimate are applicable for rotating beams on equal declination scans, and can possibly be extended to simple approximations to other scan strategies. [ABSTRACT FROM AUTHOR]

Observational cosmology has indeed made a very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation measurements of CMB anisotropy and, more recently, polarization has played a very important role. Besides precise determination of various parameters of the "standard" cosmological model, observations have also established some important basic tenets that underlie models of cosmology and structure formation in the universe — "acausally" correlated initial perturbations in a flat, statistically isotropic universe, adiabatic nature of primordial density perturbations. These are consistent with the expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early universe. Further, gravitational instability is the established mechanism for structure formation from these initial perturbations. In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature of inflation — the primordial gravitational wave background. [ABSTRACT FROM AUTHOR]

We use joint likelihood analyses of combinations of fifteen cosmic microwave background (CMB) anisotropy data sets from the DMR, UCSB South Pole 1994, Python I–III, ARGO, MAX 4 and 5, White Dish, OVRO, and SuZIE experiments to constrain cosmogonies. We consider open and spatially-flat-Λ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω[sub 0] in the range 0.1–1, baryonic-mass density parameter Ω[sub B] in the range (0.005–0.029)h[sup -2], and age of the universe t[sub 0] in the range (10–20) Gyr. Marginalizing over all parameters but Ω[sub 0], the data favor Ω[sub 0] ≃ 0.9–1 (0.4–0.6) flat-Λ (open) models. The range in deduced Ω[sub 0] values is partially a consequence of the different combinations of smaller-angular-scale CMB anisotropy data sets used in the analyses, but more significantly a consequence of whether the DMR quadrupole moment is accounted for or ignored in the analysis. While the open model is difficult to reconcile with the results of analyses of more recent CMB anisotropy data, the lower values of Ω[sub 0] found in this case are more easily reconciled with dynamical estimates of this parameter. For both flat-Λ and open models, after marginalizing over all other parameters, a lower Ω[sub B]h[sup 2] ≃ 0.005–0.009 is favored. This is also marginally at odds with estimates from more recent CMB anisotropy data and some estimates from standard nucleosynthesis theory and observed light element abundances. For both sets of models a younger universe with t[sub 0] ≃ 12–15 Gyr is favored, consistent with other recent non-CMB indicators. We emphasize that we have performed an exact analysis (i.e. from data to parameter likelihoods without the intermediate step of data compression into band powers), and since we consider only a small number of data sets, these results are tentative. More importantly, the analyses here do not rule out the currently favored flat-Λ model with Ω[sub 0] ~ 0.3, nor the larger Ω[sub B]h[sup 2] values favored by some other data. [ABSTRACT FROM AUTHOR]

We use Owens Valley Radio Observatory (OVRO) cosmic microwave background (CMB) anisotropy data to constrain cosmological parameters. We account for the OVRO beamwidth and calibration uncertainties, as well as the uncertainty induced by the removal of non-CMB foreground contamination. We consider open and spatially-∇ at-∇ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω[SUB0] in the range 0.1-1, baryonic-mass density parameter Ω[SUBB] in the range (0.005-0.029)h[SUP-2], age of the universe t[SUB0] in the range (10-20) Gyr. Marginalizing over all parameters but Ω[SUB0], the OVRO data favors an open (spatially-flat-∇) model with Ω[SUB0] ≃ 0.33 (0.1). At the 2σ confidence level model normalizations deduced from the OVRO data are mostly consistent with those deduced from the DMR, UCSB South Pole 1994, Python I-III, ARGO, MAX 4 and 5, White Dish, and SuZIE data sets. [ABSTRACT FROM AUTHOR]

Recent measurements of the temperature field of the cosmic microwave background (CMB) provide tantalizing evidence for violation of statistical isotropy (SI) that constitutes a fundamental tenet of contemporary cosmology. CMB space based missions, WMAP, and Planck have observed a 7% departure in the SI temperature field at large angular scales. However, due to higher cosmic variance at low multipoles, the significance of this measurement is not expected to improve from any future CMB temperature measurements. We demonstrate that weak lensing of the CMB due to scalar perturbations produces a corresponding SI violation in B modes of CMB polarization at smaller angular scales. The measurability of this phenomenon depends upon the scales (l range) over which power asymmetry is present. Power asymmetry, which is restricted only to l < 64 in the temperature field, cannot lead to any significant observable effect from this new window. However, this effect can put an independent bound on the spatial range of scales of hemispherical asymmetry present in the scalar sector. [ABSTRACT FROM AUTHOR]