arXiv subjects

A. N. Taylor

Publications and source records attributed to A. N. Taylor.

88 records · Page 5Linked to original sources

arXiv2001

Imaging the 3-D cosmological mass distribution with weak gravitational lensing

I show how weak gravitational lensing can be used to image the 3-D mass distribution in the Universe. An inverse relation to the lensing equation, relating the lensing potential evaluated at each source to the full 3-D Newtonian potential, is derived. I consider the normal modes of the lensing problem and clarify the equations using a small-angle approximation. Finally I consider the prospects of using this method to estimate the 3-D matter distribution from a realistic galaxy lensing survey.

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arXiv2001

Probing the distribution of dark matter in the Abell 901/902 supercluster with weak lensing

We present a weak shear analysis of the Abell 901/902 supercluster, composed of three rich clusters at z=0.16. Using a deep R-band image from the 0.5 x 0.5 degree MPG/ESO Wide Field Imager together with supplementary B-band observations, we build up a comprehensive picture of the light and mass distributions in this region. We find that, on average, the light from the early-type galaxies traces the dark matter fairly well, although one cluster is a notable exception to this rule. The clusters themselves exhibit a range of mass-to-light (M/L) ratios, X-ray properties, and galaxy populations. We attempt to model the relation between the total mass and the light from the early-type galaxies with a simple scale-independent linear biasing model. We find M/L_B=130h for the early type galaxies with zero stochasticity, which, if taken at face value, would imply Omega_m < 0.1. However, this linear relation breaks down on small scales and on scales equivalent to the average cluster separation (approximately 1 Mpc), demonstrating that a single M/L ratio is not adequate to fully describe the mass-light relation in the supercluster. Rather, the scatter in M/L ratios observed for the clusters supports a model incorporating non-linear biasing or stochastic processes. Finally, there is a clear detection of filamentary structure connecting two of the clusters, seen in both the galaxy and dark matter distributions, and we discuss the effects of cluster-cluster and cluster-filament interactions as a means to reconcile the disparate descriptions of the supercluster.

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arXiv2000

Gravitino production in the warm inflationary scenario

We estimate the production of gravitinos during and after the end of a period of warm inflation, a model in which radiation is produced continuously as the field rolls down the potential producing dissipation. We find that gravitino production is efficient for models in the strong dissipation regime, with the result that standard nucleosynthesis is disrupted unless the magnitude of the inflaton potential is very small. Combining this with the constraint from the thermal production of adiabatic density perturbations we find the dissipation rate must be extraordinarily strong, or that the potential is very flat.

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arXiv2000

Gravitational lens magnification by Abell 1689: Distortion of the background galaxy luminosity function

Gravitational lensing magnifies the luminosity of galaxies behind the lens. We use this effect to constrain the total mass in the cluster Abell 1689 by comparing the lensed luminosities of background galaxies with the luminosity function of an undistorted field. Since galaxies are assumed to be a random sampling of luminosity space, this method is not limited by clustering noise. We use photometric redshift information to estimate galaxy distance and intrinsic luminosity. Knowing the redshift distribution of the background population allows us to lift the mass/background degeneracy common to lensing analysis. In this paper we use 9 filters observed over 12 hours with the Calar Alto 3.5m telescope to determine the redshifts of 1000 galaxies in the field of Abell 1689. Using a complete sample of 151 background galaxies we measure the cluster mass profile. We find that the total projected mass interior to 0.25h^(-1)Mpc is (0.48 +/- 0.16) * 10^(15)h^(-1) solar masses, where our error budget includes uncertainties from the photometric redshift determination, the uncertainty in the off-set calibration and finite sampling. This result is in good agreement with that found by number count and shear-based methods and provides a new and independent method to determine cluster masses.

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arXiv2000

Depletion of background galaxies due to the cluster lens CL0024+1654: U and R band observations

We have obtained U and R band observations of the depletion of background galaxies due to the gravitational lensing of the galaxy cluster CL0024+1654 (z=0.39). The radial depletion curves show a significant depletion in both bands within a radius of 40''-70'' from the cluster center. This is the first time depletion is detected in the U band. This gives independent evidence for a break in the slope of the U band luminosity function at faint magnitudes. The radially averaged R band depletion curve is broader and deeper than in the U band. The differences can be attributed to the wavelength dependence of the slope of the luminosity function and to the different redshift distribution of the objects probed in the two bands. We estimate the Einstein radius of a singular isothermal sphere lens model using maximum likelihood analysis. Adopting a slope of the number counts of 0.2 and using the background density found beyond 150'' from the cluster center we find an Einstein radius of 17''+/-3'' and 25''+/-3'' in the U and R band, respectively. When combined with the redshift of the single background galaxy at z=1.675 seen as four giant arcs around 30'' from the cluster center, these values indicate a median redshift in the range 0.7 to 1.1 for the U_AB > 24 mag and R_AB > 24 mag populations.

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arXiv2000

Application of Data Compression Methods to the Redshift-space distortions of the PSCz galaxy catalogue

We apply a spherical harmonic analysis to the Point Source Redshift Survey (PSCz), to compute the real-space galaxy power spectrum and the degree of redshift distortion caused by peculiar velocities. We employ new parameter eigenvector and hierarchical data compression techniques, allowing a much larger number of harmonic modes to be included, and correspondingly smaller error bars. Using 4644 harmonic modes, compressed to 2278, we find that the IRAS redshift-space distortion parameter is $β= 0.39 \pm 0.12$ and the amplitude of galaxy clustering on a scale of $k=0.1 \Mpch$ is $Δ_{\rm gal}(0.1)=0.42 \pm 0.02$. Combining these we find the amplitude of mass perturbations is $Δ_m(0.1)=(0.16\pm0.04) Ω_m^{-0.6}$. A preliminary model fitting analysis combining the PSCz amplitudes with the CMB and abundance of clusters yields the cosmological matter density parameter $Ω_m=0.16\pm 0.03$, the amplitude of primordial perturbations $Q=(8.4\pm 3.8) \times 10^{-5}$, and the IRAS bias parameter $b=0.84\pm 0.28$.

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arXiv2000

Perturbation Spectra in the Warm Inflationary Scenario

We investigate the phenomenology of warm inflation and present generic results about the evolution of the inflaton and radiation fields. The general conditions required for warm inflation to take place are derived and discussed. A comprehensive approach is presented for the generation of thermally induced adiabatic and isocurvature perturbations and the amplitude of their spectra calculated. In addition we derive the ratio of tensor-to-scalar perturbations and find the spectral indices for adiabatic, isocurvature and tensor perturbations formed in the warm inflationary era. These results are presented in a simplified and compact approach that is generally applicable. Our results are illustrated by inflation models with polynomial and exponential potentials. We compare our analytic results against numerical models and find excellent agreement. Finally, presently available data is used to put constraints on warm inflation and we discuss how near--future observations may distinguish the warm inflationary scenario from standard supercooled inflation. The main observable difference is the different scalar-to- tensor ratio, and that the consistency relation between this and the slope of tensor perturbations does not hold for warm inflation.

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arXiv2000

Redshift Distortions and Clustering in the PSCz Survey

We have constrained the redshift-distortion parameter $β\equiv Ω^{0.6}/b$ and the real-space power spectrum of the IRAS PSCz survey using a spherical-harmonic redshift-distortion analysis combined with a data compression method which is designed to deal with correlated parameters. Our latest result, $β=0.4 \pm 0.1$, strongly rules out $β=1$.

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arXiv1999

The IRAS PSCz Dipole

We use the PSCz IRAS galaxy redshift survey to analyze the cosmological galaxy dipole out to a distance 300 h$^{-1}$ Mpc. The masked area is filled in three different ways, firstly by sampling the whole sky at random, secondly by using neighbouring areas to fill a masked region, and thirdly using a spherical harmonic analysis. The method of treatment of the mask is found to have a significant effect on the final calculated dipole. The conversion from redshift space to real space is accomplished by using an analytical model of the cluster and void distribution, based on 88 nearby groups, 854 clusters and 163 voids, with some of the clusters and all of the voids found from the PSCz database. The dipole for the whole PSCz sample appears to have converged within a distance of 200 $h^{-1}$Mpc and yields a value for $β= Ω^{0.6}/b$ = 0.75 (+0.11,-0.08), consistent with earlier determinations from IRAS samples by a variety of methods. For b = 1, the $2-σ$ range for $Ω_{o}$ is 0.43-1.02. The direction of the dipole is within 13$^o$ of the CMB dipole, the main uncertainty in direction being associated with the masked area behind the Galactic plane. The improbability that further major contributions to the dipole amplitude will come from volumes larger than those surveyed here means that the question of the origin of the CMB dipole is essentially resolved.

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arXiv1999

Spherical Harmonic Analysis of the PSCz Galaxy Catalogue: Redshift distortions and the real-space power spectrum

We apply the formalism of spherical harmonic decomposition to the galaxy density field of the IRAS PSCz redshift survey. The PSCz redshift survey has almost all-sky coverage and includes IRAS galaxies to a flux limit of 0.6 Jy. Using maximum likelihood methods to examine (to first order) the distortion of the galaxy pattern due to redshift coordinates, we have measured the parameter β= Ω^{0.6}/b. We also simultaneously measure (a) the undistorted amplitude of perturbations in the galaxy distribution when a parameterised power spectrum is assumed, or (b) the shape and amplitude of the real-space power spectrum if the band-power in a set of passbands is measured in a step- wise fashion. These methods are extensively tested on a series of CDM, ΛCDM and MDM simulations and are found to be unbiased. We obtain consistent results for the subset of the PSCz catalogue with flux above 0.75 Jy but inclusion of galaxies to the formal flux limit of the catalogue gives variations which are larger than our internal errors. For the 0.75 Jy catalogue we find, in the case of a parameterised power spectrum, β=0.58\pm0.26 and the amplitude of the real space power measured at wavenumber k=0.1 h/Mpc is Δ_{0.1}=0.42 \pm 0.03. Freeing the shape of the power spectrum we find that β=0.47\pm 0.16 (conditional error), and Δ_{0.1}=0.47 \pm 0.03. The shape of the real-space power spectrum is consistent with a Γ= 0.2 CDM-like shape parameter, but does not strongly rule out a number of other models. Finally by combining our estimate of the amplitude of galaxy clustering and the distortion parameter we find the amplitude of mass fluctuations on a scale k=0.1 \hmpc is Δ_ρ= 0.24 Ω_0^{-0.6}$, with an uncertainty of 50%.

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arXiv1998

Gravitational Lens Magnification and the Mass of Abell 1689

We present the first application of lens magnification to measure the absolute mass of a galaxy cluster; Abell 1689. The absolute mass of a galaxy cluster can be measured by the gravitational lens magnification of a background galaxy population by the cluster potential. The lensing signal is complicated by the variation in number counts due to galaxy clustering and shot-noise, and by additional uncertainties in relating magnification to mass in the strong lensing regime. Clustering and shot-noise can be dealt with using maximum likelihood methods. Local approximations can then be used to estimate the mass from magnification. Alternatively if the lens is axially symmetric we show that the amplification equation can be solved nonlocally for the surface mass density and the tangential shear. In this paper we present the first maps of the total mass distribution in Abell 1689, measured from the deficit of lensed red galaxies behind the cluster. Although noisier, these reproduce the main features of mass maps made using the shear distortion of background galaxies but have the correct normalisation, finally breaking the ``sheet-mass'' degeneracy that has plagued lensing methods based on shear. We derive the cluster mass profile in the inner 4' (0.48 Mpc/h). These show a profile with a near isothermal surface mass density κ= (0.5+/-0.1)(θ/1')^{-1} out to a radius of 2.4' (0.28Mpc/h), followed by a sudden drop into noise. We find that the projected mass interior to 0.24 h^{-1}$Mpc is M(<0.24 Mpc/h)=(0.50+/- 0.09) \times 10^{15} Msol/h. We compare our results with masses estimated from X-ray temperatures and line-of-sight velocity dispersions, as well as weak shear and lensing arclets and find all are in fair agreement for Abell 1698.

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arXiv1997

Design and analysis of redshift surveys

In this paper we consider methods of analysis and optimal design of redshift surveys. In the first part, we develop a formalism for analysing galaxy redshift surveys which are essentially two-dimensional, such as thin declination slices. The formalism is a power spectrum method, using spherical coordinates, allowing the distorting effects of galaxy peculiar velocities to be calculated to linear order on the assumption of statistical isotropy but without further approximation. In this paper, we calculate the measured two-dimensional power for a constant declination strip, widely used in redshift surveys. We present a likelihood method for estimating the three-dimensional real-space power spectrum and the redshift distortion simultaneously, and show that for thin surveys of reasonable depth, the large-scale 3D power cannot be measured with high accuracy. The redshift distortion may be estimated successfully, and with higher accuracy if the 3D power spectrum can be measured independently, for example from a large-scale sky-projected catalogue. In the second part, we show how a 3D survey design can be optimized to measure the power spectrum, considering whether areal coverage is more important than depth, and whether the survey should be sampled sparsely or not. We show quite generally that width is better than depth, and show how the optimal sparse-sampling fraction, f, depends on the power, P, to be measured. For a Schechter luminosity function, a simple optimization fP \simeq 500 h^{-3} Mpc^3 is found.

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arXiv1996

Nonlinear Cosmological Power Spectra in Real and Redshift--Space

We present an expression for the nonlinear evolution of the cosmological power spectrum based on following Lagrangian trajectories. This is simplified using the Zel'dovich approximation to trace particle displacements, assuming Gaussian initial conditions. The model is found to exhibit the transfer of power from large to small scales expected in self- gravitating fields. We have extended this analysis into redshift-space and found a solution for the nonlinear, anisotropic redshift-space power spectrum in the limit of plane--parallel redshift distortions. The quadrupole-to- monopole ratio is calculated for the case of power-law initial spectra. We find that the shape of this ratio depends on the shape of the initial spectrum, but when scaled to linear theory depends only weakly on the redshift-space distortion parameter, $β$. The point of zero-crossing of the quadrupole, $k_0$, is found to obey a scaling relation. This model is found to be in agreement with $N$-body simulations on scales down to the zero-crossing of the quadrupole, although the wavenumber at zero-crossing is underestimated. These results are applied to the quadrupole--monopole ratio found in the merged QDOT+1.2 Jy IRAS redshift survey. We have estimated that the distortion parameter is constrained to be $β>0.5$ at the $95 \%$ level. The local primordial spectral slope is not well constrained, but analysis suggests $n \approx -2$ in the translinear regime. The zero-crossing scale of the quadrupole is $k_0=0.5 \pm 0.1 h/Mpc$ and from this we infer the amplitude of clustering is $σ_8=0.7 \pm 0.05$. We suggest that the success of this model is due to nonlinear redshift--space effects arising from infall onto caustics and is not dominated by virialised cluster cores.

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arXiv1994

A Spherical Harmonic Analysis of Redshift Space

We re-examine the effects of redshift space distortion in all-sky galaxy redshift surveys in the formalism of spherical harmonics. Within this framework we show how one can treat both the large-scale linear effects, and the small-scale nonlinear clustering, exactly to first order. The method also allows in principle a determination of the power spectrum of perturbations, requiring no assumptions beyond that of linear theory. The method therefore offers significant advantages over Fourier techniques when dealing with all-sky surveys. We apply our likelihood analysis to both simulated data, and real data, using the IRAS 1.2-Jy galaxy catalogue, for which we find a maximum likelihood $β\simeq 1.1\pm 0.3$, and a real-space fluctuation amplitude corresponding to $σ_{8,{\rm IRAS}} = 0.68\pm 0.05$.

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arXiv1994

Mapping Cluster Mass Distributions via Gravitational Lensing of Background Galaxies

We present a new method for measuring the projected mass distributions of galaxy clusters. The gravitational amplification is measured by comparing the joint distribution in redshift and magnitude of galaxies behind the cluster with that of field galaxies. We show that the total amplification is directly related to the surface mass density in the weak field limit, and so it is possible to map the mass distribution of the cluster. The method is shown to be limited by discreteness noise and galaxy clustering behind the lens. Galaxy clustering sets a lower limit to the error along the redshift direction, but a clustering independent lensing signature may be obtained from the magnitude distribution at fixed redshift. Statistical techniques are developed for estimating the surface mass density of the cluster. We extend these methods to account for any obscuration by cluster halo dust, which may be mapped independently of the dark matter. We apply the method to a series of numerical simulations and show the feasibility of the approach. We consider approximate redshift information, and show how the mass estimates are degraded.

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arXiv1993

Reconstruction Analysis I.: Redshift--space deprojection in the quasi--nonlinear regime

We present a new method for extracting the true 3-d velocity and density fields from the nonlinear redshift--space projected density field. The method is based on the nonlinear, nonlocal transformation of the density field. We assume a curl--free velocity field, although in the formulation presented here this assumption can be dropped. Toy models with special symmetry are used to test the intrinsic accuracy of the method compared to linear theory. Finding significant improvement we then test the method in more detail on N--body simulations, considering the problems associated with sampling the density field using sparse, magnitude--limited galaxy redshift surveys. A method of estimating the magnitude of shot--noise effects on the deprojected velocity field is derived. We find there is a good correlation between the true and deprojected density and velocity fields, even in the mildly nonlinear regime, provided that on large scales galaxies trace the mass. An initial application is made to the IRAS--QDOT all--sky redshift survey.

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