http://www.ita.uni-heidelberg.de/~jmerten/misc/bartelmann_weaklensing.pdf

Weak Gravitational Lensing

We develop and test a method for measuring the gravitational lensing induced distortion of faint background galaxies. We first describe how we locate the galaxies and measure a 2-component `polarisation' or ellipticity statistic $e_\alpha$ whose expectation value should be proportional to the gravitational shear $\gamma_\alpha$. We then show that an anisotropic instrumental psf perturbs the polarisation by $\delta e_\alpha = P^s_{\alpha\beta} p_\beta$, where $p_\alpha$ is a measure of the psf anisotropy and $P^s_{\alpha\beta}$ is the `linearised smear polarisability tensor'. By estimating $P^s_{\alpha\beta}$ for each object we can determine $p_\alpha$ from the foreground stars and apply a correction $-P^s_{\alpha\beta}p_\beta$ to the galaxies. We test this procedure using deep high-resolution images from HST which are smeared with an anisotropic psf and then have noise added to simulate ground-based observations. We find that the procedure works very well. A similar analysis yields a linear shear polarisability tensor $P^\gamma_{\alpha\beta}$ which describes the response to a gravitational shear. This calibrates the polarisation-shear relation, but only for galaxies which are well resolved. To empirically calibrate the effect of seeing on the smaller galaxies we artificially stretch HST images to simulate lensing and then degrade them as before. These experiments provide a rigorous and exacting test of the method under realistic conditions. They show that it is possible to remove the effect of instrumental psf anisotropy, and that the method provides an efficient and quantitative measurement of the gravitational shear.

A Method for Weak Lensing Observations

We measure cosmic weak lensing shear power spectra with the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalog covering 137 deg^2 of the sky. Thanks to the high effective galaxy number density of ∼17 arcmin^−2, even after conservative cuts such as a magnitude cut of i < 24.5 and photometric redshift cut of 0.3 ≤ z ≤ 1.5, we obtain a high-significance measurement of the cosmic shear power spectra in four tomographic redshift bins, achieving a total signal-to-noise ratio of 16 in the multipole range 300 ≤ l ≤ 1900. We carefully account for various uncertainties in our analysis including the intrinsic alignment of galaxies, scatters and biases in photometric redshifts, residual uncertainties in the shear measurement, and modeling of the matter power spectrum. The accuracy of our power spectrum measurement method as well as our analytic model of the covariance matrix are tested against realistic mock shear catalogs. For a flat Λ cold dark matter model, we find |$S\,_{8}\equiv \sigma _8(\Omega _{\rm m}/0.3)^\alpha =0.800^{+0.029}_{-0.028}$| for α = 0.45 (⁠|$S\,_8=0.780^{+0.030}_{-0.033}$| for α = 0.5) from our HSC tomographic cosmic shear analysis alone. In comparison with Planck cosmic microwave background constraints, our results prefer slightly lower values of S_8, although metrics such as the Bayesian evidence ratio test do not show significant evidence for discordance between these results. We study the effect of possible additional systematic errors that are unaccounted for in our fiducial cosmic shear analysis, and find that they can shift the best-fit values of S_8 by up to ∼0.6 σ in both directions. The full HSC survey data will contain several times more area, and will lead to significantly improved cosmological constraints.

Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data

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 zs=1 and ∼30% at zs=0.5. We conclude that, depending on the intrinsic-alignment model, the GI correlation may be the dominant contaminant of the lensing signal and can even affect cross spectra between widely separated bins. We describe two ways to constrain this effect, one based on density-shear correlations and one based on scaling of the cross correlation tomography signal with redshift.

/pdf/intrinsic-alignment-lensing-interference-as-a-contaminant-of-3sll0guvvl.pdf

Intrinsic alignment-lensing interference as a contaminant of cosmic shear

Cosmic shear is the distortion of images of distant galaxies due to weak gravitational lensing by the large-scale structure in the Universe. Such images are coherently deformed by the tidal field of matter inhomogeneities along the line of sight. By measuring galaxy shape correlations, we can study the properties and evolution of structure on large scales as well as the geometry of the Universe. Thus, cosmic shear has become a powerful probe into the nature of dark matter and the origin of the current accelerated expansion of the Universe. Over the last years, cosmic shear has evolved into a reliable and robust cosmological probe, providing measurements of the expansion history of the Universe and the growth of its structure. We review here the principles of weak gravitational lensing and show how cosmic shear is interpreted in a cosmological context. Then we give an overview of weak-lensing measurements, and present the main observational cosmic-shear results since it was discovered 15 years ago, as well as the implications for cosmology. We then conclude with an outlook on the various future surveys and missions, for which cosmic shear is one of the main science drivers, and discuss promising new weak cosmological lensing techniques for future observations.

https://iopscience.iop.org/article/10.1088/0034-4885/78/8/086901/pdf

Cosmology with cosmic shear observations: a review

We measure the alignment of galaxy ellipticities in the local Universe over a range of scales using digitized photographic data from the {SuperCOSMOS} Sky Survey. We find for a magnitude cut of {bJ{\textless}20.5}, corresponding to a median galaxy redshift of z{\textasciitilde}0.1, and 2??106 galaxies, that the galaxy ellipticities exhibit a non-zero correlation over a range of scales between 1 and 100arcmin. We detect this correlation in two colours, {bJ} and R and, most significantly, in the cross-correlation between the two bands, which is less likely to be contaminated by systematics. In particular, we measure the variance of mean galaxy ellipticities, ??2(??), in square angular cells on the sky as a function of cell size and find that it lies in the range, 2??10- 4{\textgreater}=??2(??){\textgreater}{\textasciitilde}1??10-5 for cell side lengths of between 15{\textless}=??{\textless}=100arcmin. Considering the low median redshift of the galaxies in the sample and hence the relatively low effective cross-section for lensing of these galaxies by the large-scale structure of the Universe, we propose that we have detected an intrinsic alignment of galaxy ellipticities. We compare our results with recent analytical and numerical predictions made for intrinsic galaxy alignment and find good agreement. We discuss the importance of these results for measuring cosmic shear from upcoming shallow surveys (e.g. the Sloan Digital Sky Survey) and we outline how these measurements could possibly be used to constrain models of galaxy formation and/or measure the mass distribution in the local Universe.

/pdf/measurement-of-intrinsic-alignments-in-galaxy-ellipticities-29k0jv8sjs.pdf

Measurement of intrinsic alignments in galaxy ellipticities

The first season of survey around the site of Tell Jerablus Tahtani, conducted in March and April 2006, demonstrated the existence of occupations from the Neolithic to the Early Islamic period. Tell Jerablus Tahtani was fringed to the west by a lower settlement of Late Uruk and early third millennium BC date, at which time settlement was also evident at Tell Sha'ir to the west and at Duluk near the junction with the Sajour. Tells formed the main mode of occupation during the Early and Middle Bronze Ages, but this pattern of occupation broke down during the Hellenistic through Late Antique periods when a more dispersed pattern of rural settlements and small towns developed. The landscape became progressively more “busy” during the Hellenistic through Late Antique periods, when the presence of conduits, canals and other landscape features attest to both increasingly intensive and extensive systems of land use.

/pdf/archaeology-in-the-land-of-carchemish-landscape-surveys-in-210jy2o8cs.pdf

Archaeology in the land of Carchemish : landscape surveys in the area of Jerablus Tahtani, 2006.

Paleo-environmental evolution of the Larnaca Salt Lakes (Cyprus) and the relationship to second millennium BC settlement

This paper explores the role of waterways in shaping the settlement landscape of south-east Cyprus during the second millennium bc. Particular emphasis is placed on the proposed use of the Gialias river, in conjunction with overland portages, for transporting bulk commodities from the island's interior to the coast. The geopolitical characteristics of Alashiya, as known from eastern Mediterranean court correspondence, are considered with reference to adjacent riverine and maritime regions. A dominant trend of continuity in settlement and societal development is identified for south-east Cyprus as a whole throughout the period under review.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S006824541300004X

Waterways and the political geography of south-east cyprus in the second millennium bc

Scholarship of the Bronze-to-Iron Age transition in the northern Levantine littoral has traditionally stressed a major disjuncture in settlement and societal development c. 1200 BCE, concurrent with the destruction and abandonment of the Ugaritic capital at Ras Shamra. Based upon a reinterpretation of the archaeological remains at Tell Sūkās, this study argues for a degree of regional continuity in cultural lineage from the mid-second to early first millennium BCE, based upon the proposed identification of a previously unknown example of ancestral veneration.

Ancestral veneration and the settlement history of tell sūkās

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