[Show abstract][Hide abstract] ABSTRACT: Tests of gravity on large-scales in the universe can be made using both imaging and spectroscopic surveys. The former allow for measurements of weak lensing, galaxy clustering and cross-correlations such as the ISW effect. The latter probe galaxy dynamics through redshift space distortions. We use a set of basic observables, namely lensing power spectra, galaxy-lensing and galaxy-velocity cross-spectra in multiple redshift bins (including their covariances), to estimate the ability of upcoming surveys to test gravity theories. We use a two-parameter description of gravity that allows for the Poisson equation and the ratio of metric potentials to depart from general relativity. We find that the combination of imaging and spectroscopic observables is essential in making robust tests of gravity theories. The range of scales and redshifts best probed by upcoming surveys is discussed. We also compare our parametrization to others used in the literature, in particular the gamma parameter modification of the growth factor. Comment: 18 pages, 10 figures, to be submitted
Preview · Article · Jun 2009 · Physical review D: Particles and fields
[Show abstract][Hide abstract] ABSTRACT: We investigate three potential sources of bias in distance estimations made assuming that a very simple estimator of the baryon acoustic oscillation (BAO) scale provides a standard ruler. These are the effects of the non-linear evolution of structure, scale-dependent bias and errors in the survey window function estimation. The simple estimator used is the peak of the smoothed correlation function, which provides a variance in the BAO scale that is close to optimal, if appropriate low-pass filtering is applied to the density field. While maximum-likelihood estimators can eliminate biases if the form of the systematic error is fully modeled, we estimate the potential effects of un- or mis-modelled systematic errors. Non-linear structure growth using the Smith et al. (2003) prescription biases the acoustic scale by <0.3% at z>1 under the correlation-function estimator. The biases due to representative but simplistic models of scale-dependent galaxy bias are below 1% at z>1 for bias behaviour in the realms suggested by halo model calculations, which is expected to be below statistical errors for a 1000 sq.degs. spectroscopic survey. The distance bias due to a survey window function errors is given in a simple closed form and it is shown it has to be kept below 2% not to bias acoustic scale more than 1% at z=1, although the actual tolerance can be larger depending upon galaxy bias. These biases are comparable to statistical errors for ambitious surveys if no correction is made for them. We show that RMS photometric zero-point errors (at limiting magnitude 25 mag) below 0.14 mag and 0.01 mag for redshift z=1 (red galaxies) and z=3 (Lyman-break galaxies), respectively, are required in order to keep the distance estimator bias below 1%.
Preview · Article · Jun 2006 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: 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 ratio 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 2df-Sloan LRG and Quasar (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 ΔΣ around 259 609 spectroscopic galaxies in the SDSS; by measuring ΔΣ with different source samples we establish consistency of the results at the 10 per cent level (1σ). 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.
Preview · Article · Jul 2005 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We calculate the systematic errors in the weak gravitational lensing power spectrum which would be caused by spatially varying calibration (i.e. multiplicative) errors, such as might arise from uncorrected seeing or extinction variations. The systematic error is fully described by the angular two-point correlation function of the systematic in the case of the 2D lensing that we consider here. We investigate three specific cases: Gaussian, ``patchy'' and exponential correlation functions. In order to keep systematic errors below statistical errors in future LSST-like surveys, the spatial variation of calibration should not exceed 3% rms. This conclusion is independently true for all forms of correlation function we consider. The relative size the E- and B-mode power spectrum errors does, however, depend upon the form of the correlation function, indicating that one cannot repair the E-mode power spectrum systematics by means of the B-mode measurements. Comment: 8 pages, 3 figures. Changes reflect PRD published version
[Show abstract][Hide abstract] ABSTRACT: Galaxy–galaxy lensing has emerged as a powerful probe of the dark matter haloes 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 < Δγ < +0.0066 (99.9 per cent confidence, including identified systematics), which limits
contamination of the galaxy–galaxy lensing signal to at most ∼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 ratio or poorly resolved source galaxies are used.
Full-text · Article · Sep 2004 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We present a theoretical analysis of galaxy–galaxy lensing in the context of halo models with cold dark matter motivated dark matter profiles. The model enables us to distinguish between the central galactic and non-central group/cluster contributions. We apply the model to the recent Sloan Digital Sky Survey (SDSS) measurements with known redshifts and luminosities of the lenses. This allows one to model accurately the mass distribution of a local galaxy population around and above L*. We find that the virial mass of an L* galaxy is M200= (5 − 10) × 1011h−1 M⊙ depending on the colour of the galaxy. This value varies significantly with galaxy morphology, with M* for late types being lower by a factor of 10 in u′, a factor of 7 in g′ and a factor of 2.5–3 in r′, i′ and z′ relative to early types. The fraction of non-central galaxies in groups and clusters is estimated to be below 10 per cent for late types and around 30 per cent for early types. Using the luminosity dependence of the signal, we find that for early types the virial halo mass M scales with luminosity as M∝L1.4±0.2 in red bands above L*. This shows that the virial mass-to-light ratio (M/L) is increasing with luminosity for galaxies above L*, as predicted by theoretical models. The virial mass-to-light ratio in the i′ band is 17 (45) h M⊙/L⊙ at L* for late (early) types. Combining this result with cosmological baryon fraction, one finds that 70 (25) per cent h−1ΥiΩm/12Ωb of baryons within r200 are converted to stars at L*, where Υi is the stellar mass-to-light ratio in the i′ band. This indicates that for both early- and late-type galaxies around L* a significant fraction of all the baryons in the halo is transformed into stars.
Preview · Article · Aug 2002 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We use semi-analytic models of galaxy formation combined with high-resolution N-body simulations to make predictions for galaxy—dark matter correlations and apply them to galaxy—galaxy lensing. We analyse
cross-power spectra between the dark matter and different galaxy samples selected by luminosity, colour or star formation
rate. We compare the predictions with the recent detection by the Sloan Digital Sky Survey (SDSS). We show that the correlation
amplitude and the mean tangential shear depend strongly on the luminosity of the sample on scales below 1 h−1 Mpc, reflecting the correlation between the galaxy luminosity and the halo mass. The cross-correlation cannot, however, be
used to infer the halo profile directly because different halo masses dominate on different scales and because not all galaxies
are at the centres of the corresponding haloes. We compute the redshift evolution of the cross-correlation amplitude and compare
it with those of galaxies and dark matter. We also compute the galaxy—dark matter correlation coefficient and show that it
is close to unity on scales above 1 h−1 Mpc for all considered galaxy types. This would allow one to extract the bias and the dark matter power spectrum on large
scales from the galaxy and galaxy—dark matter correlations.
Preview · Article · Feb 2001 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: Matter inhomogeneities along the line of sight deflect the cosmic microwave background (CMB) photons originating at the last scattering surface at redshift $z \sim 1100$. These distortions modify the pattern of CMB polarization. We identify specific combinations of Stokes $Q$ and $U$ parameters that correspond to spin 0,$\pm 2$ variables and can be used to reconstruct the projected matter density. We compute the expected signal to noise as a function of detector sensitivity and angular resolution. With Planck satellite the detection would be at a few $\sigma$ level. Several times better detector sensitivity would be needed to measure the projected dark matter power spectrum over a wider range of scales, which could provide an independent confirmation of the projected matter power spectrum as measured from other methods. Comment: 17 pages, 5 figures, accepted for publication in PRD
[Show abstract][Hide abstract] ABSTRACT: We show the advantages of representing thedynamics of simple mechanical systems described by anatural Lagrangian, in terms of geodesics of aRiemannian (or pseudo-Riemannian) space with anadditional dimension. We demonstrate how generaltrajectories of simple mechanical systems can be putinto one-toone correspondence with the geodesics of asuitable manifold. Two different ways in which thegeometry of the configuration space can be obtained froma higher dimensional model are presented and compared:(1) by a straightforward projection, and (2) as a spacegeometry of a quotient space obtained by the action of the timelike Killing vectorgenerating a stationary symmetry of a background spacegeometry with an additional dimension. The second modelis more informative and coincides with the so-called optical model of the line-of-sight geometry. Onthe base of this model we study the behavior of nearbygeodesics to detect their sensitive dependence oninitial conditions — the key ingredient ofdeterministic chaos. The advantage of such a formulation isits invariant character.
No preview · Article · May 1998 · International Journal of Theoretical Physics