Reconstruction within the Zeldovich approximation

The Zeldovich approximation, 1st order Lagrangian perturbation theory, provides a good description of the clustering of matter and galaxies on large scales. The acoustic feature in the large-scale correlation function of galaxies imprinted by sound waves in the early Universe has been successfully used as a `standard ruler' to constrain the expansion history of the Universe. The standard ruler can be improved if a process known as density field reconstruction is employed. In this paper we develop the Zeldovich formalism to compute the correlation function of biased tracers in both real- and redshift-space using the simplest reconstruction algorithm with a Gaussian kernel and compare to N-body simulations. The model qualitatively describes the effects of reconstruction on the simulations, though its quantitative success depends upon how redshift-space distortions are handled in the reconstruction algorithm.Comment: 7 pages, 3 figures, to appear in MNRA

Motion in place: a case study of archaeological reconstruction using motion capture

Human movement constitutes a fundamental part of the archaeological process, and of any interpretationof a site’s usage; yet there has to date been little or no consideration of how movement observed (incontemporary situations) and inferred (in archaeological reconstruction) can be documented. This paper reports on the Motion in Place Platform project, which seeks to use motion capture hardware and data totest human responses to Virtual Reality (VR) environments and their real-world equivalents using round houses of the Southern British Iron Age which have been both modelled in 3D and reconstructed in the present day as a case study. This allows us to frame questions about the assumptions which are implicitlyhardwired into VR presentations of archaeology and cultural heritage in new ways. In the future, this will lead to new insights into how VR models can be constructed, used and transmitted

The Zeldovich approximation

This year marks the 100th anniversary of the birth of Yakov Zel'dovich. Amongst his many legacies is the Zel'dovich approximation for the growth of large-scale structure, which remains one of the most successful and insightful analytic models of structure formation. We use the Zel'dovich approximation to compute the two-point function of the matter and biased tracers, and compare to the results of N-body simulations and other Lagrangian perturbation theories. We show that Lagrangian perturbation theories converge well and that the Zel'dovich approximation provides a good fit to the N-body results except for the quadrupole moment of the halo correlation function. We extend the calculation of halo bias to 3rd order and also consider non-local biasing schemes, none of which remove the discrepancy. We argue that a part of the discrepancy owes to an incorrect prediction of inter-halo velocity correlations. We use the Zel'dovich approximation to compute the ingredients of the Gaussian streaming model and show that this hybrid method provides a good fit to clustering of halos in redshift space down to scales of tens of Mpc.Comment: 11 pages, 7 figures. Minor modifications to match version accepted by MNRAS. Erratum added to shear equations in Appendix, no conclusions change

The mass of a halo

We discuss the different definitions of the mass of a halo in common use and how one may convert between them. Using N-body simulations we show that mass estimates based on spherical averages are much more tightly correlated with each other than with masses based on the number of particles in a halo. The mass functions pertaining to some different mass definitions are estimated and compared to the `universal form' of Jenkins et al. (2000). Using a different simulation pipeline and a different cosmological model we show that the mass function is well fit by the Jenkins et al. (2000) fitting function, strengthening the claim to universality made by those authors. We show that care must be taken to match the definitions of mass when using large N-body simulations to bootstrap scaling relations from smaller hydrodynamical runs to avoid observationally significant bias in the predictions for abundances of objects.Comment: 6 pages,to appear in A&

Shot noise and reconstruction of the acoustic peak

We study the effect of noise in the density field, such as would arise from a finite number density of tracers, on reconstruction of the acoustic peak within the context of Lagrangian perturbation theory. Reconstruction performs better when the density field is determined from denser tracers, but the gains saturate at n~1e-4(h/Mpc)^3. For low density tracers it is best to use a large smoothing scale to define the shifts, but the optimum is very broad.Comment: 2 pages, 1 figure

Anisotropies in the CMB

The ten's of micro-Kelvin variations in the temperature of the cosmic microwave background (CMB) radiation across the sky encode a wealth of information about the Universe. The full-sky, high-resolution maps of the CMB that will be made in the next decade should determine cosmological parameters to unprecedented precision and sharply test inflation and other theories of the early Universe.Comment: 7 pages, 7 figures, to appear in proceedings of DPF9

The redshift space power spectrum in the halo model

Recently there has been a lot of attention focussed on a virialized halo-based approach to understanding the properties of the matter and galaxy power spectrum. We show that this model allows a natural treatment of the large and small scale redshift space distortions, which we develop here, which extends the pedagogical value of the approach.Comment: 4 pages, 2 figures, submitted to MNRA

Polarization of the CMB Anisotropy

I review why we expect the CMB anisotropy to be polarized, what we can learn from studying polarization and the level of the experimental challenge it presents. A discussion of current and future polarization sensitive experiments will focus on the expected sensitivity of PLANCK.Comment: To appear in the Proceedings of the MPA/ESO Conference "Evolution of large-scale structure", Garching, August 199