Lensing Studies with Diffuse Backgrounds

The current weak lensing measurements of the large scale structure are mostly related to statistical study of background galaxy ellipticities. We consider a possibility to extend lensing studies with intrinsically unresolved sources and suggest that spatial fluctuations in the integrated diffuse emission from these sources can be used for a lensing reconstruction. Examples of upcoming possibilities include the diffuse background generated by dusty starburst galaxies at far-infrared wavelengths, first stars and galaxies in near-infrared wavelengths, and the background related to 21 cm emission by neutral gas in the general intergalactic medium prior to reionization. While methods developed to extract lensing information from cosmic microwave background (CMB) temperature and polarization data can be easily modified to study lensing properties using diffuse backgrounds at other wavelengths, we suggest that the lensing extraction from these backgrounds using higher order non-Gaussian clustering information alone may not be the best approach. In contrast to CMB anisotropies, reasons for this include the lack of features in the clustering power spectrum such that the resulting lensing modification to the angular power spectrum of low-redshift diffuse backgrounds, at arcminute angular scales, is insignificant. While the use of low redshift backgrounds for lensing studies will be challenging, due to confusing foregrounds among other reasons, the use of suggested backgrounds will extend the reconstruction of the integrated matter power spectrum out to redshifts of 15 to 30, and will bridge the gap between current and upcoming galaxy lensing studies out to, at most, a redshift of a few and planned weak lensing studies with CMB out to the last scattering surface at a redshift of 1100.Comment: 25 pages, 4 figure

Extragalactic Background Light: Measurements and Applications

This review covers the measurements related to the extragalactic background light (EBL) intensity from gamma-rays to radio in the electromagnetic spectrum over 20 decades in the wavelength. The cosmic microwave background (CMB) remains the best measured spectrum with an accuracy better than 1%. The measurements related to the cosmic optical background (COB), centered at 1 microns, are impacted by the large zodiacal light associated with interplanetary dust in the inner Solar system. The best measurements of COB come from an indirect technique involving Gamma-ray spectra of bright blazars with an absorption feature resulting from pair-production off of COB photons. The cosmic infrared background (CIB) peaking at around 100 microns established an energetically important background with an intensity comparable to the optical background. This discovery paved the path for large aperture far-infrared and sub-millimeter observations resulting in the discovery of dusty, starbursting galaxies. Their role in galaxy formation and evolution remains an active area of research in modern-day astrophysics. The extreme UV background remains mostly unexplored and will be a challenge to measure due to the high Galactic background and absorption of extragalactic photons by the intergalactic medium at these EUV/soft X-ray energies. We also summarize our understanding of the spatial anisotropies and angular power spectra of intensity fluctuations. We motivate a precise direct measurement of the COB between 0.1 to 5 microns using a small aperture telescope observing either from the outer Solar system, at distances of 5 AU or more, or out of the ecliptic plane. Other future applications include improving our understanding of the background at TeV energies and spectral distortions of CMB and CIB.Comment: 24 pages, 3 figures; invited review for Royal Society Open Science (RSOS), see http://rsos.royalsocietypublishing.org. Electronic files and data related to Figure 1 are available at http://herschel.uci.ed

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).Comment: 27 PRD Pages, 15 figures; Submitted to Phys. Rev.

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.Comment: 9 PRD Pages, 5 figures; Submitted to Phys. Rev.