arXiv subjects

Asantha Cooray

Publications and source records attributed to Asantha Cooray.

At least 325 records · Page 18Linked to original sources

arXiv2002

Separation of Gravitational-Wave and Cosmic-Shear Contributions to Cosmic Microwave Background Polarization

Inflationary gravitational waves (GW) contribute to the curl component in the polarization of the CMB. Cosmic shear--gravitational lensing of the CMB-- converts a fraction of the dominant gradient polarization to the curl component. Higher-order correlations can be used to map the cosmic shear and subtract this contribution to the curl. Arcminute resolution will be required to pursue GW amplitudes smaller than those accessible by Planck. The finite cutoff in CMB power at small scales leads to a minimum detectable GW amplitude corresponding to an inflation energy near 10^15 GeV.

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arXiv2002

Large Scale Structure in an Era of Precision CMB Measurements

The advent of high signal-to-noise cosmic microwave background (CMB) anisotropy experiments now allow detailed studies on the statistics related to temperature fluctuations. The existence of acoustic oscillations in the anisotropy power spectrum is now established with the clear detection of the first, and to a lesser confidence the second and the third, peak. Beyond the acoustic peak structure associated with CMB photon temperature fluctuations, we study the possibility for an observational detection of oscillations in the large scale structure (LSS) matter power spectrum due to baryons. We also suggest a new cosmological test using the angular power spectrum of dark matter halos, or clusters of galaxies detected via wide-field surveys of the large scale structure. The standard rulers of the proposed test involve overall shape of the matter power spectrum and baryon oscillation peaks in projection. The test allows a measurement of the angular diameter distance as a function of redshift, similar to the distance to the last scattering surface from the first acoustic peak in the temperature anisotropy power spectrum. The simultaneous detection of oscillations in both photons and baryons will provide a strong, and a necessary, confirmation of our understanding related to the physics during the recombination era. The proposed studies can be carried out with a combined analysis of CMB data from missions such as the MAP and the large scale structure data from missions such as the DUET.

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arXiv2002

After Acoustic Peaks: What's Next in CMB?

The advent of high signal-to-noise cosmic microwave background (CMB) anisotropy experiments has allowed detailed studies on the power spectrum of temperature fluctuations. The existence of acoustic oscillations in the anisotropy power spectrum is now established with the detection of the first two, and possibly the third, peaks. Beyond the acoustic peak structure, we consider cosmological and astrophysical information that can be extracted by pushing anisotropy observations to fine angular scales with higher resolution instruments. At small scales, a variety of contributions allow the use of CMB photons as a probe of the large scale structure: we outline possible studies related to understanding detailed physical properties such as the distribution of dark matter, baryons and pressure, and ways to measure the peculiar, transverse and rotational velocities of virialized halos such as galaxy clusters. Beyond the temperature, we consider several useful aspects of the CMB polarization and comment on an ultimate goal for future CMB experiments involving the direct detection of inflationary gravity-waves through their distinct signature in the curl-type polarization.

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arXiv2002

Weak Lensing of the CMB: Extraction of Lensing Information from the Trispectrum

We discuss the four-point correlation function, or the trispectrum in Fourier space, of CMB temperature and polarization anisotropies due to the weak gravitational lensing effect by intervening large scale structure. We discuss the squared temperature power spectrum as a probe of this trispectrum and, more importantly, as an observational approach to extracting the power spectrum of the deflection angle associated with the weak gravitational lensing effect on the CMB. We extend previous discussions on the trispectrum and associated weak lensing reconstruction from CMB data by calculating non-Gaussian noise contributions, beyond the previously discussed dominant Gaussian noise. Non-Gaussian noise contributions are generated by lensing itself and by the correlation between the lensing effect and other foreground secondary anisotropies in the CMB such as the Sunyaev-Zel'dovich (SZ) effect. When the SZ effect is removed from temperature maps using its spectral dependence, we find these additional non-Gaussian noise contributions to be an order of magnitude lower than the dominant Gaussian noise. If the noise-bias due to the dominant Gaussian part of the temperature squared power spectrum is removed, then these additional non-Gaussian contributions provide the limiting noise level for the lensing reconstruction. The temperature squared power spectrum allows a high signal-to-noise extraction of the lensing deflections and a confusion-free separation of the curl (or B-mode) polarization due to inflationary gravitational waves from that due to lensed gradient (or E-mode) polarization. The small angular scale temperature and polarization anisotropy measurements provide a novel approach to weak lensing studies, complementing the approach based on galaxy ellipticities.

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arXiv2002

Kinetic Sunyaev-Zel'dovich effect from halo rotation

We discuss the kinetic Sunyaev-Zel'dovich (SZ) contribution to cosmic microwave background (CMB) temperature fluctuations due to coherent rotational velocity component of electrons within halos. This effect produces a distinct dipole-like temperature distribution across the the cluster, and provides a promising way to measure the angular momentum distribution of gas inside clusters. Information obtained from such a measurement may provide new insights to the origin and evolution of angular momentum in hierarchical structure formation theory. For typical, well relaxed, clusters of mass a few times 10$^{14}$ M$_{\sun}$, the peak fluctuation is of the order a few $μ$K, depending on the rotational velocity and the inclination angle of the rotational axis. For clusters which had underwent a recent merger, the contribution to temperature fluctuations could be even larger. This dipole signature is similar to the one produced by lensed CMB towards galaxy clusters, though the lensing contribution spans a larger angular extent than the one due to rotational scattering as the former depends on the gradient of the cluster potential. Since the lensing contribution towards clusters are aligned with the large scale CMB gradient, when higher resolution observations towards clusters are combined with a wide field CMB map, these two effects can be separated. An additional, but less important, source of confusion is the dipolar pattern produced by the moving-lens effect involving, again, the gradient of the cluster potential and the transverse velocity. The angular power spectrum of temperature anisotropies produced by the halo rotation is expected to be smaller than those due to the thermal SZ and peculiar velocity kinetic SZ effects.

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arXiv2002

Second Order Corrections to Large Scale Structure Weak Lensing: Background Source Clustering

We discuss the second order contributions to lensing statistics resulting from the clustering of background sources from which galaxy shape measurements are made in weak lensing experiments. In addition to a previously discussed contribution to the lensing skewness, background source clustering also contributes to the two-point correlation function, such as the angular power spectrum of convergence or shear. At arcminute scales or above, the second order contribution to the angular power spectrum of convergence due to source clustering is below the level of a few percent. The background clustering of sources also results in a non-Gaussian contribution to the power spectrum covariance of weak lensing convergence through a four-point correlation function or a trispectrum in Fourier space. The increase in variance is, at most, a few percent relative to the Gaussian contribution while the band powers are also correlated at the few percent level. The non-Gaussian contributions due to background source clustering is at least an order of magnitude smaller than those resulting from non-Gaussian aspects of the large scale structure due to the non-linear evolution of gravitational perturbations. We suggest that the background source clustering is unlikely to affect the precision measurements of cosmology from upcoming weak lensing surveys.

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arXiv2002

Second Order Corrections to Weak Lensing by Large-Scale Structure

We calculate corrections to the power spectrum predictions of weak lensing by large scale structure due to higher order effects in the gravitational potential. Using a perturbative approach to third order in transverse displacements, we calculate a second order correction to the angular power spectra of E and B mode shear and convergence resulting from dropping the so-called Born approximation, where one integrates along the unperturbed photon path. We also consider a correction to the power spectra from the coupling between lenses at different redshifts. Both effects generate B-mode shear and the latter also causes a net rotation of the background galaxy images. We show all these corrections are at least two orders of magnitude below the convergence or E-mode power and hence relevant only to future ultra high precision measurements. These analytical calculations are consistent with previous numerical estimates and validate the use of current large scale structure weak lensing predictions for cosmological studies and future use of B-modes as a monitor of systematic effects.

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arXiv2001

How Can We Study the Local Universe with CMB Photons?

We show how observations of temperature fluctuations in cosmic microwave background (CMB) can be used to extract information related to the large scale structure, including dark matter distribution, pressure and halo velocities involving the line of sight, transverse and rotational components. The frequency spectrum can be used to separate the SZ effect from thermal fluctuations. The measurement of higher order correlations in CMB can be used to extract effects involving lensing and kinetic SZ effects. A high signal-to-noise arcminute scale CMB experiment can be used to construct the weak lensing convergence, which is useful given that the background source, CMB anisotropies at the last scattering surface, is well understood.

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arXiv2001

Baryon Oscillations in the Large Scale Structure

We study the possibility for an observational detection of oscillations due to baryons in the matter power spectrum and suggest a new cosmological test using the angular power spectrum of halos. The "standard rulers" of the proposed test involve overall shape of the matter power spectrum and baryon oscillation peaks in projection, as a function of redshift. Since oscillations are erased at non-linear scales, traces at redshifts greater than 1 are generally preferred. Given the decrease in number density of clusters at high redshift, however, one is forced to use tracers corresponding to galaxy groups and galaxies themselves.

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arXiv2001

The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation

We discuss the correlation between late-time integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB) temperature anisotropies and the large scale structure of the local universe. This correlation has been proposed and studied in the literature as a probe of the dark energy and its physical properties. We consider a variety of large scale structure tracers suitable for a detection of the ISW effect via a cross-correlation. In addition to luminous sources, we suggest the use of tracers such as dark matter halos or galaxy clusters. A suitable catalog of mass selected halos for this purpose can be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ) effect surveys. With multifrequency data, the presence of the ISW-large scale structure correlation can also be investigated through a cross-correlation of the frequency cleaned SZ and CMB maps. While convergence maps constructed from lensing surveys of the large scale structure via galaxy ellipticities are less correlated with the ISW effect, lensing potentials that deflect CMB photons are strongly correlated and allow, probably, the best mechanism to study the ISW-large scale structure correlation with CMB data alone.

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arXiv2001

Weak Lensing of the CMB: Power Spectrum Covariance

We discuss the non-Gaussian contribution to the power spectrum covariance of cosmic microwave background (CMB) anisotropies resulting through weak gravitational lensing angular deflections and the correlation of deflections with secondary sources of temperature fluctuations generated by the large scale structure, such as the integrated Sachs-Wolfe effect and the Sunyave-Zel'dovich effect. This additional contribution to the covariance of binned angular power spectrum, beyond the well known cosmic variance and any associated instrumental noise, results from a trispectrum, or a four point correlation function, in temperature anisotropy data. With substantially wide bins in multipole space, the resulting non-Gaussian contribution from lensing to the binned power spectrum variance is insignificant out to multipoles of a few thousand and is not likely to affect the cosmological parameter estimation through acoustic peaks and the damping tail. The non-Gaussian contribution to covariance, however, should be considered when interpreting binned CMB power spectrum measurements at multipoles of a few thousand corresponding to angular scales of few arcminutes and less.

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arXiv2001

Non-linear Integrated Sachs-Wolfe Effect

We discuss the non-linear extension to the integrated Sachs-Wolfe effect (ISW) resulting from the divergence of the large scale structure momentum density field. The non-linear ISW effect leads to an increase in the total ISW contribution by roughly two orders of magnitude at l ~ 1000. This increase, however, is still below the cosmic variance limit of the primary anisotropies; at further small angular scales, secondary effects such as gravitational lensing and the kinetic Sunyaev-Zel'dovich (SZ) effect dominates the non-linear ISW power spectrum. We show this second-order non-linear ISW contribution is effectively same as the contribution previously described as a lensing effect due to the transverse motion of gravitational lenses and well known as the Kaiser-Stebbins effect under the context of cosmic strings. Due to geometrical considerations, there is no significant three point correlation function, or a bispectrum, between the linear ISW effects and its non-linear extension. The non-linear ISW contribution can be potentially used as a probe of the transverse velocity of dark matter halos such as galaxy clusters. Due to the small contribution to temperature fluctuations, of order few tenths of micro Kelvin, however, extrating useful measurements on velocities will be challenging.

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arXiv2001

Measuring Angular Diameter Distances through Halo Clustering

Current and upcoming wide-field surveys for weak gravitational lensing and the Sunyaev-Zel'dovich effect will generate mass-selected catalogues of dark matter halos with internal or followup photometric redshift information. The angular power spectrum of these halos provides additional information that complements the previously-studied number counts. In particular, using the shape of the linear power spectrum as a standard ruler that is calibrated by cosmic microwave background measurements, we find that a survey of 4000 sqr. deg. and a mass threshold of 10^14 M_sun can be used to determine the comoving angular diameter distance as a function of redshift. In principle, this test also allows an absolute calibration of the distance scale and measurement of the Hubble constant. This test is largely insensitive to the details of halo mass measurements, mass function, and halo bias. Determination of these quantities would further allow a measurement of the linear growth rate of fluctuations.

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arXiv2001

Applications of Halo Approach to Non-Linear Large Scale Structure Clustering

We present astrophysical applications of the recently popular halo model to describe large scale structure clustering. We formulate the power spectrum, bispectrum and trispectrum of dark matter density field in terms of correlations within and between dark matter halos. The halo approach uses results from numerical simulations and involves a profile for dark matter, a mass function for halos, and a description of halo biasing with respect to the linear density field. This technique can easily be extended to describe clustering of any property of the large scale structure, such as galaxies, baryons and pressure, provided that one formulate the relationship between such properties and dark matter. In detail, we discuss applications of the halo model for several observational probes of the local universe involving weak gravitational lensing, thermal Sunyaev-Zel'dovich (SZ) effect and the kinetic SZ effect. We also propose a new cosmological test using the redshift evolution of the angular power spectrum of halos and using a calibrated linear power spectrum, which acts as an effective standard ruler (Summary).

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arXiv2001

Squared temperature-temperature power spectrum as a probe of the CMB bispectrum

It is now well known that mode-coupling effects associated with certain secondary effects generate higher order correlations in cosmic microwave background (CMB) temperature anisotropies, beyond the two-point function. In order to extract the non-Gaussian signal at the three-point level, we suggest a two-point statistic in the form of an angular power spectrum involving correlations between squared temperature and temperature anisotropies. This power spectrum contains compressed information from the bispectrum and can be easily measured in data with the same techniques that have been considered for the measurement of the usual temperature-temperature anisotropy power spectrum. We study the proposed power spectrum resulting from the non-Gaussian signal generated by correlations involved with gravitational lensing angular deflections in CMB and the Sunyave-Zel'dovich (SZ) effect due to large scale pressure fluctuations. Using the Planck frequency cleaned CMB and SZ maps, the CMB^2-SZ power spectrum provides a direct estimate of the cross-power between lensing angular deflections and the SZ effect. Through an optimal filter applied to the squared CMB map, the proposed statistic allows one to obtain all information from the lensing-SZ bispectrum. The observational measurement of the lensing-SZ cross-correlation is useful to understand the relation between large scale structure pressure and dark matter fluctuations.

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arXiv2001

Non-Gaussian Aspects of Thermal and Kinetic Sunyaev-Zel'dovich Effects

We discuss non-Gaussian effects associated with the local large-scale structure contributions to the Cosmic Microwave Background (CMB) anisotropies through the thermal Sunyaev-Zel'dovich (SZ) effect. The non-Gaussianities associated with the SZ effect arise from the existence of a significant four-point correlation function in large scale pressure fluctuations. Using the full covariance matrix of the SZ thermal power spectrum, we study astrophysical uses of the SZ effect and discuss the extent to which gas properties can be derived from a measurement of the SZ power spectrum. With the SZ thermal effect separated in temperature fluctuations using its frequency information, the kinetic SZ effect is expected to dominate the CMB temperature fluctuations at small angular scales. The presence of the SZ kinetic effect can be determined through a cross-correlation between the SZ thermal and a CMB map at small scales. We suggest a statistic that can be used to study the correlation between pressure traced by the SZ thermal effect and the baryons traced by the SZ kinetic effect involving the cross-power spectrum constructed through squared temperatures instead of the usual temperature itself. Through a signal-to-noise calculation, we show that future small angular scale multi-frequency CMB experiments, sensitive to multipoles of a few thousand, will be able to measure the cross-correlation of SZ thermal and SZ kinetic effect through a temperature squared power spectrum (abridged).

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arXiv2001

Gravitational Lens Image Separations versus Redshift as a Cosmological Test

This preprint, or a revised version, was never published as it was based on and included unacknowledged material from Helbig, P. (1997) `The Delta theta-z_s relation as a cosmological test', first presented at the 12th Potsdam Cosmology Workshop (V. M"uller, S. Gottl"ober, J.-P. M"ucket & J. Wambsganss (eds), Singapore: World Scientific, pp. 319--20) and that I wanted this paper, rather than mine, to receive full credit for the work under discussion. I am withdrawing my preprint to further emphasize that I take no credit and note that astro-ph/9804104 by P. Helbig (1998) (MNRAS, 298, 2, 395 (1998)) contains fully detailed arguments, using the complete JVAS sample and other techniques, against the claim made by Park & Gott in astro-ph/9702173 (1997) (ApJ, 489, 476).

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arXiv2000

Power Spectrum Covariance of Weak Gravitational Lensing

Weak gravitational lensing observations probe the spectrum and evolution of density fluctuations and the cosmological parameters which govern them. At low redshifts, the non-linear gravitational evolution of large scale structure produces a non-Gaussian covariance in the shear power spectrum measurements that affects their translation into cosmological parameters. Using the dark matter halo approach, we study the covariance of binned band power spectrum estimates and the four point function of the dark matter density field that underlies it. We compare this semi-analytic estimate to results from N-body numerical simulations and find good agreement. We find that for a survey out to z ~ 1, the power spectrum covariance increases the errors on cosmological parameters determined under the Gaussian assumption by about 15%.

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