Search

The GMRT reionization effort aims to map out the large scale structure of the Universe during the epoch of reionization (EoR). Removal of polarized Galactic emission is a difficult part of any 21 cm EoR program, and we present new upper limits to diffuse polarized foregrounds at 150 MHz. We find no high significance evidence of polarized emission in our observed field at mid galactic latitude (J2000 08h26m+26). We find an upper limit on the 2-dimensional angular power spectrum of diffuse polarized foregrounds of [l^2 C_l/(2 PI)]^{1/2}< 3K in frequency bins of width 1 MHz at 300 0.03 h/Mpc, k < 0.1 h/Mpc. This can be compared to the expected EoR signal in total intensity of [k^3 P(k)/ (2 PI^2) ]^{1/2} ~ 10 mK. We find polarized structure is substantially weaker than suggested by extrapolation from higher frequency observations, so the new low upper limits reported here reduce the anticipated impact of these foregrounds on EoR experiments. We discuss Faraday beam and depth depolarization models and compare predictions of these models to our data. We report on a new technique for polarization calibration using pulsars, as well as a new technique to remove broadband radio frequency interference. Our data indicate that, on the edges of the main beam at GMRT, polarization squint creates ~ 3% leakage of unpolarized power into polarized maps at zero rotation measure. Ionospheric rotation was largely stable during these solar minimum night time observations., Comment: 17 pages, 6 figures, 2 tables; changed figures, added appendices. To appear in MNRAS

We perform a statistical weak lensing analysis of dark matter profiles around tracers of halo mass from galactic- to cluster-size halos. In this analysis we use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236 groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823 MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range of richness. Together these three samples allow a determination of the density profiles of dark matter halos over three orders of magnitude in mass, from 10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent with an NFW or Einasto profile on scales outside the central region. We find that the NFW concentration parameter c_{200b} decreases with halo mass, from around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results for the Einasto profile. The slope (\beta) is in agreement with theoretical predictions, while the amplitude is about two standard deviations below the predictions for this mass and redshift, but we note that the published values in the literature differ at a level of 10-20% and that for a proper comparison our analysis should be repeated in simulations. We discuss the implications of our results for the baryonic effects on the shear power spectrum: since these are expected to increase the halo concentration, the fact that we see no evidence of high concentrations on scales above 20% of the virial radius suggests that baryonic effects are limited to small scales, and are not a significant source of uncertainty for the current weak lensing measurements of the dark matter power spectrum. [ABRIDGED], Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that are included in v2 here on arXiv

The subject of cosmological hydrogen recombination has received much attention recently because of its importance to predictions for and cosmological constraints from CMB observations. While the central role of the two-photon decay 2s->1s has been recognized for many decades, high-precision calculations require us to consider two-photon decays from the higher states ns,nd->1s (n>=3). Simple attempts to include these processes in recombination calculations have suffered from physical problems associated with sequences of one-photon decays, e.g. 3d->2p->1s, that technically also produce two photons. These correspond to resonances in the two-photon spectrum that are optically thick, necessitating a radiative transfer calculation. We derive the appropriate equations, develop a numerical code to solve them, and verify the results by finding agreement with analytic approximations to the radiative transfer equation. The related processes of Raman scattering and two-photon recombination are included using similar machinery. Our results show that early in recombination the two-photon decays act to speed up recombination, reducing the free electron abundance by 1.3% relative to the standard calculation at z=1300. However we find that some photons between Ly-alpha and Ly-beta are produced, mainly by 3d->1s two-photon decay and 2s->1s Raman scattering. At later times these photons redshift down to Ly-alpha, excite hydrogen atoms, and act to slow recombination. Thus the free electron abundance is increased by 1.3% relative to the standard calculation at z=900. The implied correction to the CMB power spectrum is neligible for the recently released WMAP and ACBAR data, but at Fisher matrix level will be 7 sigma for Planck. [ABRIDGED], Comment: Matches PRD accepted version. 28 pages, 12 figures

We develop an improved mass tracer for clusters of galaxies from optically observed parameters, and calibrate the mass relation using weak gravitational lensing measurements. We employ a sample of ~ 13,000 optically-selected clusters from the Sloan Digital Sky Survey (SDSS) maxBCG catalog, with photometric redshifts in the range 0.1-0.3. The optical tracers we consider are cluster richness, cluster luminosity, luminosity of the brightest cluster galaxy (BCG), and combinations of these parameters. We measure the weak lensing signal around stacked clusters as a function of the various tracers, and use it to determine the tracer with the least amount of scatter. We further use the weak lensing data to calibrate the mass normalization. We find that the best mass estimator for massive clusters is a combination of cluster richness, N_{200}, and the luminosity of the brightest cluster galaxy, L_{BCG}: M_{200\bar{\rho}} = (1.27 +/- 0.08) (N_{200}/20)^{1.20 +/- 0.09} (L_{BCG}/\bar{L}_{BCG}(N_{200}))^{0.71 +/- 0.14} \times 10^{14} h^{-1} M_sun, where $\bar{L}_{BCG}(N_{200})$ is the observed mean BCG luminosity at a given richness. This improved mass tracer will enable the use of galaxy clusters as a more powerful tool for constraining cosmological parameters., Comment: 15 pages, 8 figures, accepted for publication in MNRAS, corrected typo in values of a_L after Eq. 17b

We cross-correlate large scale structure (LSS) observations from a number of surveys with CMB anisotropies from WMAP to investigate the Integrated Sachs-Wolfe (ISW) effect as a function of redshift, covering z~0.1-2.5. Our main goal is to go beyond reporting detections towards developing a reliable likelihood analysis that allows one to determine cosmological constraints from ISW observations. With this in mind we spend a considerable amount of effort in determining the redshift-dependent bias and redshift distribution b(z)*dN/dz of these samples by matching with spectroscopic observations where available, and analyzing auto-power spectra and cross-power spectra between the samples. The data sets we use are 2-Micron All Sky Survey (2MASS) samples, Sloan Digital Sky Survey (SDSS) photometric Luminous Red Galaxies, SDSS photometric quasars and NRAO VLA Sky Survey (NVSS) radio sources. We make a joint analysis of all samples constructing a full covariance matrix, which we subsequently use for cosmological parameter fitting. We report a 3.7 sigma detection of ISW combining all the datasets. We combine the ISW likelihood function with weak lensing of CMB and CMB power spectrum to constrain the equation of state of dark energy and the curvature of the Universe. While ISW does not significantly improve the constraints in the simplest 6-parameter flat Lambda CDM model, it improves constraints on 7-parameter models with curvature by a factor of 3.2 (relative to WMAP alone) to Omega_K=-0.004^{+0.014}_{-0.020}, and with dark energy equation of state by 15% to w=-1.01^{+0.30}_{-0.40}. (Abridged.), Comment: 35 pages, 18 figures, matches version to appear in PRD. Fixed bug in MCMC interface, parameter values changed by <0.2 sigma. The likelihood code can be downloaded at http://www.astro.princeton.edu/~shirley/ISW_WL.html

We investigate the correlation of gravitational lensing of the cosmic microwave background (CMB) with several tracers of large-scale structure, including luminous red galaxies (LRGs), quasars, and radio sources. The lensing field is reconstructed based on the CMB maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite; the LRGs and quasars are observed by the Sloan Digital Sky Survey (SDSS); and the radio sources are observed in the NRAO VLA Sky Survey (NVSS). Combining all three large-scale structure samples, we find evidence for a positive cross-correlation at the $2.5\sigma$ level ($1.8\sigma$ for the SDSS samples and $2.1\sigma$ for NVSS); the cross-correlation amplitude is $1.06\pm 0.42$ times that expected for the WMAP cosmological parameters. Our analysis extends other recent analyses in that we carefully determine bias weighted redshift distribution of the sources, which is needed for a meaningful cosmological interpretation of the detected signal. We investigate contamination of the signal by Galactic emission, extragalactic radio and infrared sources, thermal and kinetic Sunyaev-Zel'dovich effects, and the Rees-Sciama effect, and find all of them to be negligible., Comment: 34 pages, 6 figures, matches PRD accepted version

We investigate statistical properties of LRGs in a sample of X-ray selected galaxy clusters at intermediate redshift ($0.2\le z\le0.6$). The LRGs are selected based on carefully designed color criteria, and the cluster membership is assessed via photometric redshifts. As clusters and LRGs are both viewed as promising tracer of the underlying dark matter distribution, understanding the distribution of LRGs within clusters is an important issue. Our main findings include: 1. The halo occupation distribution of LRGs inside our cluster sample is $N(M) = k\times (M/10^{14})^{a}$ where $a=0.620\pm 0.105 $ and $k=1.425\pm0.285 $ assuming a Poisson distribution for $N(M)$. 2. The halo occupation distribution of LRGs ($N(M)$) and the satellite distribution of LRGs ($N-1(M)$) are both consistent with being Poisson. To be more quantitative, we find $Var(N)/= 1.428\pm 0.351$ and $Var(N-1)/ = 1.823 \pm 0.496$ 3. The radial profile of LRGs within clusters when fitted with a NFW profile gives a concentration of $17.5^{+7.1}_{-4.3}$ ($6.0^{+3.2}_{-1.9}$) including (excluding) BLRGs (Brightest LRGs). We also discuss the implications of these observations on the evolution of massive galaxies in clusters., Comment: 13 pages, 13 figures, 2 tables

Interpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He I. The standard treatment of these processes includes only the spontaneous two-photon decay from the 2^1S level. We extend this treatment by including five additional effects, some of which have been suggested in recent papers but whose impact on He I recombination has not been fully quantified. These are: (i) stimulated two-photon decays; (ii) two-photon absorption of redshifted HeI line radiation; (iii) two-photon decays from highly excited levels in HeI (n^1S and n^1D, with n>=3); (iv) Raman scattering; and (v) the finite width of the 2^1P^o resonance. We find that effect (iii) is highly suppressed when one takes into account destructive interference between different intermediate states contributing to the two-photon decay amplitude. Overall, these effects are found to be insignificant: they modify the recombination history at the level of several parts in 10^4., Comment: 19 pages, 11 figures, to be submitted to PRD

Upcoming precision measurements of the temperature anisotropy of the cosmic microwave background (CMB) at high multipoles will need to be complemented by a more complete understanding of recombination, which determines the damping of anisotropies on these scales. This is the third in a series of papers describing an accurate theory of HeI and HeII recombination. Here we describe the effect of Thomson scattering, the $^3$He isotope shift, the contribution of rare decays, collisional processes, and peculiar motion. These effects are found to be negligible: Thomson and $^3$He scattering modify the free electron fraction $x_e$ at the level of several $\times 10^{-4}$. The uncertainty in the $2^3P^o-1^1S$ rate is significant, and for conservative estimates gives uncertainties in $x_e$ of order $10^{-3}$. We describe several convergence tests for the atomic level code and its inputs, derive an overall $C_\ell$ error budget, and relate shifts in $x_e(z)$ to the changes in $C_\ell$, which are at the level of 0.5% at $\ell =3000$. Finally, we summarize the main corrections developed thus far. The remaining uncertainty from known effects is $\sim 0.3%$ in $x_e$., Comment: 19 pages, 15 figures, to be submitted to PRD

Precision measurements of the cosmic microwave background temperature anisotropy on scales $\ell > 500$ will be available in the near future. Successful interpretation of these data is dependent on a detailed understanding of the damping tail and cosmological recombination of both hydrogen and helium. This paper and two companion papers are devoted to a precise calculation of helium recombination. We discuss several aspects of the standard recombination picture, and then include feedback, radiative transfer in HeI lines with partial redistribution, and continuum opacity from HI photoionization. In agreement with past calculations, we find that HeII recombination proceeds in Saha equilibrium, whereas HeI recombination is delayed relative to Saha due to the low rates connecting excited states of HeI to the ground state. However, we find that at $z<2200$ the continuum absorption by the rapidly increasing HI population becomes effective at destroying photons in the HeI $2^1P^o-1^1S$ line, causing HeI recombination to finish around $z\approx 1800$, much earlier than previously estimated., Comment: 30 pages, 13 figures, to be submitted to PRD

Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright galaxies in SDSS data. Here we present a more detailed characterization of this effect, which can cause anti-correlations between gravitational lensing shear and intrinsic ellipticity (GI correlations). This measurement uses 36278 Luminous Red Galaxies (LRGs) from the SDSS spectroscopic sample with 0.153sigma detections of the effect for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ sample, we find a 2sigma detection for a bright subsample, and no detection for a fainter subsample. Fitting formulae are provided for the scaling of the GI correlations with luminosity, transverse separation, and redshift. We estimate contamination in the measurement of sigma_8 for future cosmic shear surveys on the basis of the fitted dependence of GI correlations on galaxy properties. We find contamination to the power spectrum ranging from -1.5 (optimistic) to -33 per cent (pessimistic) for a toy cosmic shear survey using all galaxies to a depth of R=24 using scales l~500. This corresponds to a bias in sigma_8 of Delta sigma_8=-0.004 (optimistic), -0.02 (central), or -0.10 (pessimistic). We provide a prescription for inclusion of this error in cosmological parameter estimation codes. The principal uncertainty is in the treatment of the L<=L* blue galaxies. Characterization of the tidal alignments of these galaxies, especially at redshifts relevant for cosmic shear, should be a high priority for the cosmic shear community. (Abridged), Comment: Matches MNRAS accepted version. Extended/updated data tables and expanded comparison to theory

Previous calculations of the pregalactic chemistry have found that a small amount of H_2, x[H_2]=n[H_2]/n[H] = 2.6e-6, is produced catalytically through the H^-, H_2^+, and HeH^+ mechanisms. We revisit this standard calculation taking into account the effects of the nonthermal radiation background produced by cosmic hydrogen recombination, which is particularly effective at destroying H^- via photodetachment. We also take into consideration the non-equilibrium level populations of H_2^+, which occur since transitions among the rotational-vibrational levels are slow compared to photodissociation. The new calculation predicts a final H_2 abundance of x[H_2] = 6e-7 for the standard cosmology. This production is due almost entirely to the H^- mechanism, with ~1 per cent coming from HeH^+ and ~0.004 per cent from H_2^+. We evaluate the heating of the diffuse pregalactic gas from the chemical reactions that produce H_2 and from rotational transitions in H_2, and find them to be negligible., Comment: 13 pages, 5 figures, MNRAS submitted

We present results of a measurement of the shape of the density profile of galaxy groups and clusters traced by 43 335 Luminous Red Galaxies (LRGs) with spectroscopic redshifts from the Sloan Digital Sky Survey (SDSS). The galaxies are selected such that they are the brightest within a cylindrical aperture, split into two luminosity samples, and modeled as the sum of stellar and dark matter components. We present a detailed investigation of many possible systematic effects that could contaminate our signal and develop methods to remove them, including a detected intrinsic alignment for galaxies within 100 kpc/h of LRGs which we remove using photometric redshift information. The resulting lensing signal is consistent with NFW profile dark matter halos; the SIS profile is ruled out at the 96 (conservatively) and 99.96 per cent confidence level (CL) for the fainter and brighter lens samples (respectively) when we fit using lensing data between 40 kpc/h and 2 Mpc/h with total signal-to-noise of 19 and 25 for the two lens samples. The lensing signal amplitude suggests that the faint and bright sample galaxies typically reside in haloes of mass (2.9+/-0.4)x10^{13} M_{sun}/h and (6.7+/-0.8)x10^{13} M_{sun}/h respectively, in good agreement with predictions based on halo spatial density with normalization lower than the 'concordance' sigma_8=0.9. When fitting for the concentration parameter in the NFW profile, we find c = 5.0+/-0.6 (stat) +/-1 (sys), and c = 5.6+/-0.6 (stat) +/-1 (sys) for the faint and bright samples, consistent with Lambda-CDM simulations. We also split the bright sample further to determine masses and concentrations for cluster-mass halos, finding mass (1.3+/-0.2)x10^{14} M_{sun}/h for the sample of LRGs brighter than -22.6 in r. (Abridged), Comment: 21 pages, 11 figures; updated to match MNRAS accepted version (minor organizational changes and additional explanatory comments)

The 21-cm hyperfine line of atomic hydrogen (HI) is a promising probe of the cosmic dark ages. In past treatments of 21-cm radiation it was assumed the hyperfine level populations of HI could be characterized by a velocity-independent ``spin temperature'' T_s determined by a competition between 21-cm radiative transitions, spin-changing collisions, and (at lower redshifts) Lyman-alpha scattering. However we show here that, if the collisional time is comparable to the radiative time, the spin temperature will depend on atomic velocity, T_s=T_s(v), and one must replace the usual hyperfine level rate equations with a Boltzmann equation describing the spin and velocity dependence of the HI distribution function. We construct here the Boltzmann equation relevant to the cosmic dark ages and solve it using a basis-function method. Accounting for the actual spin-resolved atomic velocity distribution results in up to a 2 per cent suppression of the 21-cm emissivity, and a redshift and angular-projection dependent suppression or enhancement of the linear power spectrum of 21-cm fluctuations of up to 5 per cent. The effect on the 21-cm line profile is more dramatic -- its full-width at half maximum (FWHM) can be enhanced by up to 60 per cent relative to the velocity-independent calculation. We discuss the implications for 21-cm tomography of the dark ages., Comment: 25 pages, 6 figures, submitted to Mon. Not. Roy. Astron. Soc

The relationship between galaxies and dark matter can be characterized by the halo mass of the central galaxy and the fraction of galaxies that are satellites. Here we present observational constraints from the SDSS on these quantities as a function of r-band luminosity and stellar mass using galaxy-galaxy weak lensing, with a total of 351,507 lenses. We use stellar masses derived from spectroscopy and virial halo masses derived from weak gravitational lensing to determine the efficiency with which baryons in the halo of the central galaxy have been converted into stars. We find that an L* galaxy with a stellar mass of 6x10^{10} M_{sun} is hosted by a halo with mass of 1.4x10^{12} M_{sun}/h, independent of morphology, yielding baryon conversion efficiencies of 17_{-5}^{+10} (early types) and 16_{-6}^{+15} (late types) per cent at the 95 per cent CL (statistical, not including systematic uncertainty due to assumption of a universal initial mass function, or IMF). We find that for a given stellar mass, the halo mass is independent of morphology below M_{stellar}=10^{11} M_{sun}, in contrast to typically a factor of two difference in halo mass between ellipticals and spirals at a fixed luminosity. This suggests that stellar mass is a good proxy for halo mass in this range and should be used preferentially whenever a halo mass selected sample is needed. For higher stellar masses, the conversion efficiency is a declining function of stellar mass, and the differences in halo mass between early and late types become larger, reflecting the fact that most group and cluster halos with masses above 10^{13} M_{sun} host ellipticals at the center, while even the brightest central spirals are hosted by halos of mass below 10^{13} M_{sun}. (Abridged), Comment: 19 pages, matches MNRAS accepted version

The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology, in particular for measuring the effects of dark energy on the growth of structure at low redshift. One potential source of systematic error is intrinsic alignments of ellipticities of neighbouring galaxies (II correlation) that could mimic the correlations due to lensing. A related possibility pointed out by Hirata and Seljak (2004) is correlation between the intrinsic ellipticities of galaxies and the density field responsible for gravitational lensing shear (GI correlation). We present constraints on both the II and GI correlations using 265 908 spectroscopic galaxies from the SDSS, and using galaxies as tracers of the mass in the case of the GI analysis. The availability of redshifts in the SDSS allows us to select galaxies at small radial separations, which both reduces noise in the intrinsic alignment measurement and suppresses galaxy- galaxy lensing (which otherwise swamps the GI correlation). While we find no detection of the II correlation, our results are nonetheless statistically consistent with recent detections found using the SuperCOSMOS survey. In contrast, we have a clear detection of GI correlation in galaxies brighter than L* that persists to the largest scales probed (60 Mpc/h) and with a sign predicted by theoretical models. This correlation could cause the existing lensing surveys at z~1 to underestimate the linear amplitude of fluctuations by as much as 20% depending on the source sample used, while for surveys at z~0.5 the underestimation may reach 30%. (Abridged.), Comment: 16 pages, matches version published in MNRAS (only minor changes in presentation from original version)

We present the results of attempts to detect the ellipticity of dark matter halos using galaxy-galaxy weak lensing with SDSS data. We use 2,020,256 galaxies brighter than r=19 with photometric redshifts (divided into colour and luminosity subsamples) as lenses and 31,697,869 source galaxies. We search for and identify several signal contaminants, which if not removed lead to a spurious detection. These include systematic shear that leads to a slight spurious alignment of lens and source ellipticities, intrinsic alignments (due to contamination of the source sample by physically-associated lens source pairs), and anisotropic magnification bias. We develop methods that allow us to remove these contaminants to the signal. We split the analysis into blue (spiral) and red (elliptical) galaxies. Assuming Gaussian errors as in previous work and a power-law profile, we find f_h=e_h/e_g=0.1+/-0.06 for red galaxies and -0.8+/-0.4 for blue galaxies using 20-300 kpc/h, averaged over luminosity. Inclusion of the more realistic non-Gaussian error distributions and of the NFW density profile (which predicts much smaller ellipticity of the shear for scales above the scale radius) yields 0.60+/-0.38 for ellipticals and -1.4+1.7-2.0 for spirals. While there is no concrete detection of alignment in either case, there is a suggestion in the data of a positive alignment in the brightest lens sample of ellipticals. Our results appear to be mildly inconsistent with a previously reported detection by Hoekstra et al. (2004), but more data and further tests are needed to clarify whether the discrepancy is real or a consequence of differences in the lens galaxy samples used and analysis methods., Comment: 20 pages, 8 figures, matches MNRAS accepted version (includes updated discussion of systematics, no changes to conclusions)

It has been suggested that secondary CMB anisotropies generated by neutral lithium could open a new observational window into the universe around the redshift z ~ 400, and permit a determination of the primordial lithium abundance. The effect is due to resonant scattering in the allowed LiI doublet (2s ^2S_{1/2} - 2p ^2P_{1/2,3/2}), so its observability depends on the formation history of neutral lithium. Here we show that the ultraviolet photons produced during hydrogen recombination are sufficient to keep lithium in the LiII ionization stage in the relevant redshift range and suppress the neutral fraction by ~3 orders of magnitude from previous calculations, making the lithium signature unobservable., Comment: 9 pages, 6 figures

The first UV sources in the universe are expected to have coupled the HI spin temperature to the gas kinetic temperature via scattering in the Lyman-alpha resonance [the Wouthuysen-Field (WF) effect]. By establishing an HI spin temperature different from the temperature of the CMB, the WF effect should allow observations of HI during the reionization epoch in the redshifted 21 cm line. This paper investigates four mechanisms that can affect the strength of the WF effect that were not previously considered: (1) Photons redshifting into the HI Lyman resonances may excite an H atom and result in a radiative cascade terminating in two-photon 2s->1s emission, rather than always degrading to Lyman-alpha as usually assumed. (2) The fine structure of the Lyman-alpha resonance alters the photon frequency distribution and leads to a suppression of the scattering rate. (3) The spin-flip scatterings change the frequency of the photon and cause the photon spectrum to relax not to the kinetic temperature of the gas but to a temperature between the kinetic and spin temperatures, effectively reducing the strength of the Wouthuysen-Field coupling. (4) Near line centre, a photon can change its frequency by several times the line width in a single scattering event, thus potentially invalidating the usual calculation of the Lyman-alpha spectral distortion based on the diffusion approximation. It is shown that (1) suppresses the WF coupling strength by a factor of up to ~2, while (2) and (3) are important only at low kinetic temperatures. Effect (4) has a <=3% effect for kinetic temperatures T_k>=2K. If the pre-reionization IGM was efficiently heated by X-rays, only effect (1) is important. Fitting formulae are provided for the range of T_k>=2K and Gunn-Peterson optical depth 10^5--10^7. [ABRIDGED], Comment: 17 pages, 7 figures, MNRAS accepted version

We investigate the recent suggestions by Barausse et al. (astro-ph/0501152) and Kolb et al. (hep-th/0503117) that the acceleration of the universe could be explained by large superhorizon fluctuations generated by inflation. We show that no acceleration can be produced by this mechanism. We begin by showing how the application of Raychaudhuri equation to inhomogeneous cosmologies results in several ``no go'' theorems for accelerated expansion. Next we derive an exact solution for a specific case of initial perturbations, for which application of the Kolb et al. expressions leads to an acceleration, while the exact solution reveals that no acceleration is present. We show that the discrepancy can be traced to higher order terms that were dropped in the Kolb et al. analysis. We proceed with the analysis of initial value formulation of general relativity to argue that causality severely limits what observable effects can be derived from superhorizon perturbations. By constructing a Riemann normal coordinate system on initial slice we show that no infrared divergence terms arise in this coordinate system. Thus any divergences found previously can be eliminated by a local rescaling of coordinates and are unobservable. We perform an explicit analysis of the variance of the deceleration parameter for the case of single field inflation using usual coordinates and show that the infrared divergent terms found by Barausse et al. and Kolb et al. cancel against several additional terms not considered in their analysis. Finally, we argue that introducing isocurvature perturbations does not alter our conclusion that the accelerating expansion of the universe cannot be explained by superhorizon modes., Comment: 16 pages, 1 figure, to be submitted to PRD

Weak lensing is emerging as a powerful observational tool to constrain cosmological models, but is at present limited by an incomplete understanding of many sources of systematic error. Many of these errors are multiplicative and depend on the population of background galaxies. We show how the commonly cited geometric test, which is rather insensitive to cosmology, can be used as a ratio test of systematics in the lensing signal at the 1 per cent level. We apply this test to the galaxy-galaxy lensing analysis of the Sloan Digital Sky Survey (SDSS), which at present is the sample with the highest weak lensing signal to noise and has the additional advantage of spectroscopic redshifts for lenses. This allows one to perform meaningful geometric tests of systematics for different subsamples of galaxies at different mean redshifts, such as brighter galaxies, fainter galaxies and high-redshift luminous red galaxies, both with and without photometric redshift estimates. We use overlapping objects between SDSS and the DEEP2 and 2SLAQ spectroscopic surveys to establish accurate calibration of photometric redshifts and to determine the redshift distributions for SDSS. We use these redshift results to compute the projected surface density contrast DeltaSigma around 259 609 spectroscopic galaxies in the SDSS; by measuring DeltaSigma with different source samples we establish consistency of the results at the 10 per cent level (1-sigma). We also use the ratio test to constrain shear calibration biases and other systematics in the SDSS survey data to determine the overall galaxy-galaxy weak lensing signal calibration uncertainty. We find no evidence of any inconsistency among many subsamples of the data., Comment: 39 pages, 19 figures

[Abridged] The polarization of the CMB is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the dominant CMB polarization created by density perturbations because it generates both E and B polarization modes, whereas the density perturbations create only E polarization. The limits of our ability to measure gravitational waves are thus determined by statistical and systematic errors, foregrounds, and nonlinear evolution effects such as lensing of the CMB. Usually it is assumed that most foregrounds can be removed because of their frequency dependence, however Thomson scattering of the CMB quadrupole by electrons in the Galaxy or nearby structures shares the blackbody frequency dependence of the CMB. If the optical depth from these nearby electrons is anisotropic, the polarization generated can include B modes even without tensor perturbations. We estimate this effect for the Galactic disk and nearby extragalactic structures, and find that it contributes to the B polarization at the level of ~(1--2)x10^-4\mu K per logarithmic interval in multipole L for L<30. This is well below the detectability level even for a future CMB polarization satellite. Depending on its structure and extent, the Galactic corona may be a source of B-modes comparable to the residual large-scale lensing B-mode after the latter has been cleaned using lensing reconstruction techniques. For an extremely ambitious post-Planck CMB experiment, Thomson scattering in the Galactic corona is thus a potential contaminant of the gravitational wave signal; conversely, if the other foregrounds can be cleaned out, such an experiment might be able to constrain models of the corona., Comment: 10 pages, 4 figures, to be submitted to Phys. Rev. D

We present a 2.5 sigma detection of the Integrated Sachs-Wolfe (ISW) effect and discuss the constraints it places on cosmological parameters. We cross-correlate microwave temperature maps from the WMAP satellite with a 4000 deg^2 luminous red galaxy (LRG) overdensity map measured by the Sloan Digital Sky Survey. Accurate photometric redshifts allow us to perform a reliable auto-correlation analysis of the LRGs, eliminating the uncertainty in the galaxy bias, and combined with cross correlation signal, constrains cosmological parameters -- in particular, the matter density. We find a 2.5 sigma signal in the Ka, Q, V, and W WMAP bands, after combining the information from multipoles 2 <= l < 400. This is consistent with the expected amplitude of the ISW effect, but requires a lower matter density than is usually assumed: the amplitude, parametrized by the galaxy bias assuming \Omega_M=0.3, \Omega_\Lambda=0.7 and \sigma_8=0.9, is b_g = 4.05 \pm 1.54 for V band, with similar results for the other bands. This should be compared to b_g = 1.82 \pm 0.02 from the auto-correlation analysis. These data provide only a weak confirmation (2.5 sigma) of dark energy, but provide a significant upper limit: \Omega_\Lambda=0.80_{-0.06}^{+0.03} (1 sigma)_{-0.19}^{+0.05} (2 sigma), assuming a cosmology with \Omega_M+\Omega_\Lambda=1, \Omega_b = 0.05, and \sigma_8=0.9, and w=-1. The weak cross-correlation signal rules out low matter density/high dark energy density universes and, in combination with other data, strongly constrains models with w<-1.3. We provide a simple prescription to incorporate these constraints into cosmological parameter estimation methods for (\Omega_M, \sigma_8,w). (abridged), Comment: 16 pages, 12 figures, submitted to PRD

Cosmic shear surveys have great promise as tools for precision cosmology, but can be subject to systematic errors including intrinsic ellipticity correlations of the source galaxies. The intrinsic alignments are believed to be small for deep surveys, but this is based on intrinsic and lensing distortions being uncorrelated. Here we show that the gravitational lensing shear and intrinsic shear need not be independent: correlations between the tidal field and the intrinsic shear cause the intrinsic shear of nearby galaxies to be correlated with the gravitational shear acting on more distant galaxies. We estimate the magnitude of this effect for two simple intrinsic alignment models: one in which the galaxy ellipticity is linearly related to the tidal field, and one in which it is quadratic in the tidal field as suggested by tidal torque theory. The first model predicts a gravitational-intrinsic (GI) correlation that can be much greater than the intrinsic-intrinsic (II) correlation for broad redshift distributions, and that remains when galaxies pairs at similar redshifts are rejected. The second model, in its simplest form, predicts no gravitational-intrinsic correlation. In the first model and assuming a normalization consistent with recently claimed detections of intrinsic correlations we find that the GI correlation term can exceed the usual II term by >1 order of magnitude and the intrinsic correlation induced B-mode by 2 orders of magnitude. These interference effects can suppress the lensing power spectrum for a single broad redshift bin by of order ~10% at z_s=1 and ~30% at z_s=0.5., Comment: 10 pages, 3 figs; several factors of a fixed from published version (listed in erratum), no changes to conclusions

We present the results of a search for gravitational lensing of the cosmic microwave background (CMB) in cross-correlation with the projected density of luminous red galaxies (LRGs). The CMB lensing reconstruction is performed using the first year of Wilkinson Microwave Anisotropy Probe (WMAP) data, and the galaxy maps are obtained using the Sloan Digital Sky Survey (SDSS) imaging data. We find no detection of lensing; our constraint on the galaxy bias derived from the galaxy-convergence cross-spectrum is $b_g=1.81\pm 1.92$ ($1\sigma$, statistical), as compared to the expected result of $b_g\sim 1.8$ for this sample. We discuss possible instrument-related systematic errors and show that the Galactic foregrounds are not important. We do not find any evidence for point source or thermal Sunyaev-Zel'dovich effect contamination., Comment: 24 pages, 13 figs; matches PRD accepted version

Weak lensing is a potentially robust and model-independent cosmological probe, but its accuracy is dependent on knowledge of the redshift distribution of the source galaxies used. The most robust way to determine the redshift distribution is via spectroscopy of a subsample of the source galaxies. We forecast constraints from combining CMB anisotropies with cosmic shear using a spectroscopically determined redshift distribution, varying the number of spectra $N_{spec}$ obtained from 64 to $\infty$. The source redshift distribution is expanded in a Fourier series, and the amplitudes of each mode are considered as parameters to be constrained via both the spectroscopic and weak lensing data. We assume independent source redshifts, and consider in what circumstances this is a good approximation (the sources are clustered and for narrow spectroscopic surveys with many objects this results in the redshifts being correlated). It is found that for the surveys considered and for a prior of 0.04 on the calibration parameters, the addition of redshift information make significant improvements on the constraints on the cosmological parameters; however, beyond $N_{spec}\sim$few$\times 10^3$ the addition of further spectra will make only a very small improvement to the cosmological parameters. We find that a better calibration makes large $N_{spec}$ more useful. Using an eigenvector analysis, we find that the improvement continues with even higher $N_{spec}$, but not in directions that dominate the uncertainties on the standard cosmological parameters., Comment: 8 pages, 3 figures. Final form to appear in Phys Rev D

Galaxy-galaxy lensing has emerged as a powerful probe of the dark matter halos of galaxies, but is subject to contamination if intrinsically aligned satellites of the lens galaxy are used as part of the source sample. We present a measurement of this intrinsic shear using 200,747 lens galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic sample and a sample of satellites selected using photometric redshifts. The mean intrinsic shear at transverse separations of 30--446$h^{-1}$ kpc is constrained to be $-0.0062<\Delta\gamma<+0.0066$ (99.9 per cent confidence, including identified systematics), which limits contamination of the galaxy-galaxy lensing signal to at most $\sim 15$ per cent on these scales. We present these limits as a function of transverse separation and lens luminosity. We furthermore investigate shear calibration biases in the SDSS, which can also affect galaxy-galaxy lensing, and conclude that the shear amplitude is calibrated to better than 18 per cent. This includes noise-induced calibration biases in the ellipticity, which are small for the sample considered here, but which can be more important if low signal-to-noise or poorly resolved source galaxies are used., Comment: 23 pages, 13 figures, matches MNRAS accepted version. This is a preprint of an Article accepted for publication in Monthly Notices of the Royal Astronomical Society. (c)2004 The Royal Astronomical Society

Gravity waves (GW) in the early universe generate B-type polarization in the cosmic microwave background (CMB), which can be used as a direct way to measure the energy scale of inflation. Gravitational lensing contaminates the GW signal by converting the dominant E polarization into B polarization. By reconstructing the lensing potential from CMB itself one can decontaminate the B mode induced by lensing. We present results of numerical simulations of B mode delensing using quadratic and iterative maximum-likelihood lensing reconstruction methods as a function of detector noise and beam. In our simulations we find the quadratic method can reduce the lensing B noise power by up to a factor of 7, close to the no noise limit. In contrast, the iterative method shows significant improvements even at the lowest noise levels we tested. We demonstrate explicitly that with this method at least a factor of 40 noise power reduction in lensing induced B power is possible, suggesting that T/S=10^-6 may be achievable in the absence of sky cuts, foregrounds, and instrumental systematics. While we do not find any fundamental lower limit due to lensing, we find that for high-sensitivity detectors residual lensing noise dominates over the detector noise., Comment: 6 pages, 2 figures, submitted to PRD

We use statistical inference theory to explore the constraints from future galaxy weak lensing (cosmic shear) surveys combined with the current CMB constraints on cosmological parameters, focusing particularly on the running of the spectral index of the primordial scalar power spectrum, $\alpha_s$. Recent papers have drawn attention to the possibility of measuring $\alpha_s$ by combining the CMB with galaxy clustering and/or the Lyman-$\alpha$ forest. Weak lensing combined with the CMB provides an alternative probe of the primordial power spectrum. We run a series of simulations with variable runnings and compare them to semi-analytic non-linear mappings to test their validity for our calculations. We find that a ``Reference'' cosmic shear survey with $f_{sky}=0.01$ and $6.6\times 10^8$ galaxies per steradian can reduce the uncertainty on $n_s$ and $\alpha_s$ by roughly a factor of 2 relative to the CMB alone. We investigate the effect of shear calibration biases on lensing by including the calibration factor as a parameter, and show that for our Reference Survey, the precision of cosmological parameter determination is only slightly degraded even if the amplitude calibration is uncertain by as much as 5%. We conclude that in the near future weak lensing surveys can supplement the CMB observations to constrain the primordial power spectrum., Comment: 12 pages, 10 figures, revtex4. Final form to appear in Phys Rev D

Gravitational lensing of the cosmic microwave background (CMB) polarization field has been recognized as a potentially valuable probe of the cosmological density field. We apply likelihood-based techniques to the problem of lensing of CMB polarization and show that if the B-mode polarization is mapped, then likelihood-based techniques allow significantly better lensing reconstruction than is possible using the previous quadratic estimator approach. With this method the ultimate limit to lensing reconstruction is not set by the lensed CMB power spectrum. Second-order corrections are known to produce a curl component of the lensing deflection field that cannot be described by a potential; we show that this does not significantly affect the reconstruction at noise levels greater than 0.25 microK arcmin. The reduction of the mean squared error in the lensing reconstruction relative to the quadratic method can be as much as a factor of two at noise levels of 1.4 microK arcmin to a factor of ten at 0.25 microK arcmin, depending on the angular scale of interest., Comment: matches PRD accepted version. 28 pages, 8 figs

We investigate biases induced by the conversion between the observed image shape to shear distortion in current weak lensing analysis methods. Such overall calibration biases cannot be detected by the standard tests such as E/B decomposition or calibration with stars. We find that the non-Gaussianity of point spread function has a significant effect and can lead to up to 15 per cent error on the linear amplitude of fluctuations sigma_8 depending on the method of analysis. This could explain some of the discrepancies seen in recent amplitude determinations from weak lensing. Using an elliptical Laguerre expansion method we develop a re-Gaussianization method which reduces the error to calibration error of order 1 per cent even for poorly resolved galaxies. We also discuss a new type of shear selection bias which results in up to roughly 8 percent underestimation of the signal. It is expected to scale with redshift, inducing errors in the growth factor extraction if not properly corrected for. Understanding and correcting for such effects is crucial if weak lensing is to become a high precision probe of cosmology., Comment: 23 pp, 8 figs, matches MNRAS accepted version

Future experiments will produce high-resolution temperature maps of the cosmic microwave background (CMB) and are expected to reveal the signature of gravitational lensing by intervening large-scale structures. We construct all-sky maximum-likelihood estimators that use the lensing effect to estimate the projected density (convergence) of these structures, its power spectrum, and cross-correlation with other observables. This contrasts with earlier quadratic-estimator approaches that Taylor-expanded the observed CMB temperature to linear order in the lensing deflection angle; these approaches gave estimators for the temperature-convergence correlation in terms of the CMB three-point correlation function and for the convergence power spectrum in terms of the CMB four-point correlation function, which can be biased and non-optimal due to terms beyond the linear order. We show that for sufficiently weak lensing, the maximum-likelihood estimator reduces to the computationally less demanding quadratic estimator. The maximum likelihood and quadratic approaches are compared by evaluating the root-mean-square (RMS) error and bias in the reconstructed convergence map in a numerical simulation; it is found that both the RMS errors and bias are of order 1 percent for the case of Planck and of order 10--20 percent for a 1 arcminute beam experiment. We conclude that for recovering lensing information from temperature data acquired by these experiments, the quadratic estimator is close to optimal, but further work will be required to determine whether this is also the case for lensing of the CMB polarization field., Comment: 26 pages, 5 figures

Geosynchronous orbits are appealing for solar or astrophysical observatories because they permit continuous data downlink at high rates. The radiation environment in these orbits presents unique challenges, however. This paper describes both the characteristics of the radiation environment in geosynchronous orbit and the mechanisms by which this radiation generates backgrounds in photon detectors. Shielding considerations are described, and a preliminary shielding design for the proposed Wide-Field InfraRed Survey Telescope observatory is presented as a reference for future space telescope concept studies that consider a geosynchronous orbit.

This document describes the exposure time calculator for the Wide-Field Infrared Survey Telescope (WFIRST) high-latitude survey. The calculator works in both imaging and spectroscopic modes. In addition to the standard ETC functions (e.g. background and SN determination), the calculator integrates over the galaxy population and forecasts the density and redshift distribution of galaxy shapes usable for weak lensing (in imaging mode) and the detected emission lines (in spectroscopic mode). The source code is made available for public use.