arXiv subjects

Gavin Dalton

Publications and source records attributed to Gavin Dalton.

60 records · Page 4Linked to original sources

arXiv2001

The 2dF Galaxy Redshift Survey: The power spectrum and the matter content of the universe

The 2dF Galaxy Redshift Survey has now measured in excess of 160000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct FFT-based technique. We argue that, within the k-space region 0.02<k<0.15 h Mpc^-1, the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analyzed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68% confidence limits on the total matter density times the Hubble parameter Ω_m h = 0.20 +/- 0.03, and the baryon fraction Ω_b/Ω_m = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.

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arXiv1998

The APM cluster-galaxy cross-correlation function : Constraints on Omega and galaxy bias

(abridged) We estimate the cluster-galaxy cross-correlation function (Xi_cg), from the APM galaxy and galaxy cluster surveys, both in real space from the inversion of projected statistics and in redshift space using the galaxy and cluster redshift samples. The amplitude of Xi_cg is found to be almost independent of cluster richness. At large separations, r >~5 h^-1 Mpc, Xi_cg has a similar shape to the galaxy-galaxy and cluster-cluster autocorrelation functions. Xi_cg in redshift space can be related to the real space Xi_cg by convolution with an appropriate velocity field model. Here we apply a spherical collapse model, which we have tested against N-body simulations, finding that it provides a surprisingly accurate description of the averaged infall velocity of matter into galaxy clusters. We use this model to estimate beta (Omega^{0.6}/b) and find that it tends to overestimate the true result in simulations by only ~10-30%. Application to the APM results yields beta=0.43 with beta < 0.87 at 95% confidence. We also compare the APM Xi_cg and galaxy autocorrelations to results from popular cosmological models and derive two independent estimates of the galaxy biasing expected as a function of scale. Both low and critical density CDM models require anti-biasing by a factor ~2 on scales r <~ 2 h^-1Mpc and an MDM model is consistent with a constant biasing factor on all scales. We use the velocity fields predicted from the different models to distort the APM real space cross-correlation function. Comparison with the APM redshift space Xi_cg yields an estimate of the value of Omega^0.6 needed in each model. Only the low Omega model is fully consistent with observations, with MDM marginally excluded at the ~2 sigma level.

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arXiv1997

The Power Spectrum of Rich Clusters of Galaxies on Large Spatial Scales

We present an analysis of the redshift-space power spectrum, $P(k)$, of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that $P(k)$ can be approximated by a power law, $P(k)\proptok^{n}$, with $n\approx-1.6$ over the wavenumber range $0.04\hr<k<0.1\hr$. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale $k \sim 0.03\hmpcrev$. We compare the power spectra estimated from simulated APM cluster catalogues to those estimated directly from cubical N-body simulation volumes and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers $k \simgt 0.02\hmpcrev$. These results suggest that the observed turn-over in the power spectrum may be a real feature of the cluster distribution and that we have detected the transition to a near scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turn-over in the cluster power spectrum is in good agreement with the scale of the turn-over observed in the power spectrum of APM galaxies.

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arXiv1997

The APM Galaxy Survey:- V. Catalogues of Galaxy Clusters

We describe the construction of catalogues of galaxy clusters from the APM Galaxy survey using an automated algorithm based on Abell-like selection criteria. We investigate the effects of varying several parameters in our selection algorithm, including the magnitude range, and radius from the cluster centre used to estimate the cluster richnesses. We quantify the accuracy of the photometric distance estimates by comparing with measured redshifts, and we investigate the stability and completeness of the resulting catalogues. We find that the angular correlation functions for different cluster catalogues are in good agreement with one another, and are also consistent with the observed amplitude of the spatial correlation function of rich clusters.

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arXiv1995

Variance, Skewness & Kurtosis: results from the APM Cluster Redshift Survey and model predictions

We estimate the variance $\xibar_2$, the skewness $\xibar_3$ and the kurtosis $\xibar_4$ in the distribution of density fluctuations in a complete sample from the APM Cluster Redshift Survey with 339 clusters and a mean depth $ \sim 250\Mpc$. We are able to measure the statistics of fluctuations in spheres of radius $R \simeq 5-80 \Mpc$, with reasonable errorbars. The statistics in the cluster distribution follow the hierarchical pattern $\xibar_J=S_J~\xibar_2^{J-1}$ with $S_J$ roughly constant, $S_3 \simeq 2$ and $S_4 \sim 8$. We analyse the distribution of clusters taken from N-body simulations of different dark matter models. The results are compared with an alternative method of simulating clusters which uses the truncated Zel'dovich approximation. We argue that this alternative method is not reliable enough for making quantitative predictions of $\xibar$. The N-body simulation results follow similar hierarchical relations to the observations, with $S_J$ almost unaffected by redshift distortions from peculiar motions. The standard $Ω=1$ Cold Dark Matter (CDM) model is inconsistent with either the second, third or fourth order statistics at all scales. However both a hybrid Mixed Dark Matter model and a low density CDM variant agree with the $\xibar_J$ observations.

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arXiv1994

Higher Order Statistics from the Apm Galaxy Survey

We apply a new statistics, the factorial moment correlators, to density maps obtained from the APM survey. The resulting correlators are all proportional to the two point correlation function, substantially amplified, with an amplification nearly exponential with the total rank of the correlators. This confirms the validity of the hierarchical clustering assumption on the dynamic range examined, corresponding to $0.5 \hmpc - 50 \hmpc$ in three dimensional space. The Kirkwood superposition with loop terms is strongly rejected. The structure coefficients of the hierarchy are also fitted. The high quality of the APM catalog enabled us to disentangle the various contributions from the power spectrum, small scale nonlinear clustering, and combinatorial effects, all of which affect the amplification of the correlators. These effects should appear in correlations of clusters in a similar fashion.

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