arXiv subjects

John A. Peacock

Publications and source records attributed to John A. Peacock.

90 records · Page 5Linked to original sources

arXiv2005

The 2dF Galaxy Redshift Survey: luminosity functions by density environment and galaxy type

We use the 2dF Galaxy Redshift Survey to measure the dependence of the bJ-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h-1Mpc, and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M_bJ-5log10h <-18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M_bJ-5log10h < -21. Differences in the mid to faint-end population between environments are significant: at M_bJ-5log10h=-18 early and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion which differs strikingly for early and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation.

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arXiv2004

The 2dF Galaxy Redshift Survey: stochastic relative biasing between galaxy populations

It is well known that the clustering of galaxies depends on galaxy type.Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, eta, as early or late type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the nonlinearity and stochasticity of the relative bias, with cubical cells of side 10Mpc \leq L \leq 45Mpc (h=0.7). Exact linear bias is ruled out with high significance on all scales. Power law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero `stochasticity' - i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (r_LN) of 0.958 for cells of length L=10Mpc, increasing to 0.970 by L=45Mpc. This corresponds to a stochasticity sigma_b/bhat of 0.44\pm0.02 and 0.27\pm0.05 respectively. For smaller cells, the Poisson sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semianalytic galaxy formation models: these match the data well in terms of overall level of stochasticity, variation with scale, and fraction of empty cells.

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arXiv2004

The 2dF Galaxy Redshift Survey: Spherical Harmonics analysis of fluctuations in the final catalogue

We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions. Galaxies are expected to directly follow the bulk motion of the density field on large scales, so the absolute amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties. By splitting the overdensity field into radial and angular components, we linearly model the observed distortion and obtain the cosmological constraint Omega_m^{0.6} sigma_8=0.46+/-0.06. The amplitude of the linear redshift-space distortions relative to the galaxy overdensity field is dependent on galaxy properties and, for L_* galaxies at redshift z=0, we measure beta(L_*,0)=0.58+/-0.08, and the amplitude of the overdensity fluctuations b(L_*,0) sigma_8=0.79+/-0.03, marginalising over the power spectrum shape parameters. Assuming a fixed power spectrum shape consistent with the full Fourier analysis produces very similar parameter constraints.

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arXiv2004

Substructure Analysis of Selected Low Richness 2dFGRS Clusters of Galaxies

Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure in clusters of galaxies are applied to recently obtained data from the 2dF Galaxy Redshift Survey. The sample of 25 clusters used in this study includes 16 clusters not previously investigated for substructure. Substructure is detected at or greater than the 99% CL level in at least one test for 21 of the 25 clusters studied here. From the results, it appears that low richness clusters commonly contain subclusters participating in mergers. About half of the clusters have two or more components within 0.5 h^{-1} Mpc of the cluster centroid, and at least three clusters (Abell 1139, Abell 1663, and Abell S333) exhibit velocity-position characteristics consistent with the presence of possible cluster rotation, shear, or infall dynamics. The geometry of certain features is consistent with influence by the host supercluster environments. In general, our results support the hypothesis that low richness clusters relax to structureless equilibrium states on very long dynamical time scales (if at all).

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arXiv2004

The 2dF Galaxy Redshift Survey: Clustering properties of radio galaxies

The clustering properties of local, S_{1.4 GHz} > 1 mJy, radio sources are investigated for a sample of 820 objects drawn from the joint use of the FIRST and 2dF Galaxy Redshift surveys. To this aim, we present 271 new bj < 19.45 spectroscopic counterparts of FIRST radio sources to be added to those already introduced in Magliocchetti et al. (2002). The two-point correlation function for the local radio population is found to be entirely consistent with estimates obtained for the whole sample of 2dFGRS galaxies. We estimate the parameters of the real-space correlation function xi(r)=(r/r_0)^{-γ}, r_0=6.7^{+0.9}_{-1.1} Mpc and γ=1.6\pm 0.1, where h=0.7 is assumed. Different results are instead obtained if we only consider sources that present signatures of AGN activity in their spectra. These objects are shown to be very strongly correlated, with r_0=10.9^{+1.0}_{-1.2} Mpc and γ=2\pm 0.1, a steeper slope than has been claimed in other recent works. No difference is found in the clustering properties of radio-AGNs of different radio luminosity. These results show that AGN-fuelled sources reside in dark matter halos more massive than \sim 10^{13.4} M_{\sun}},higher the corresponding figure for radio-quiet QSOs. This value can be converted into a minimum black hole mass associated with radio-loud, AGN-fuelled objects of M_{BH}^{min}\sim 10^9 M_{\sun}. The above results then suggest -at least for relatively faint radio objects -the existence of a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud AGNs; however, once the activity is triggered, there appears to be no evidence for a connection between black hole mass and level of radio output. (abridged)

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arXiv2004

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

We analyse the observed correlation between galaxy environment and H-alpha emission line strength, using volume-limited samples and group catalogues of 24968 galaxies drawn from the 2dF Galaxy Redshift Survey (Mb<-19.5) and the Sloan Digital Sky Survey (Mr<-20.6). We characterise the environment by 1) Sigma_5, the surface number density of galaxies determined by the projected distance to the 5th nearest neighbour; and 2) rho1.1 and rho5.5, three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their H-alpha equivalent width, EW(Ha). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of EW(Ha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho5.5, which is likely independent of the trend with local density, rho1.1. We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma=200-1000 km/s. Even in the lowest density environments, no more than ~70 per cent of galaxies show significant H-alpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

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arXiv2003

The 2dF Galaxy Redshift Survey: Wiener Reconstruction of the Cosmic Web

We reconstruct the underlying density field of the 2 degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 0.035<z<0.200 using the Wiener Filtering method. The Wiener Filter suppresses shot noise and accounts for selection and incompleteness effects. The method relies on prior knowledge of the 2dF power spectrum of fluctuations and the combination of matter density and bias parameters however the results are only slightly affected by changes to these parameters. We present maps of the density field in two different resolutions: 5 Mpc/h and 10 Mpc/h. We identify all major superclusters and voids in the survey. In particular, we find two large superclusters and two large local voids. A version of this paper with full set of colour maps can be found at http://www.ast.cam.ac.uk/~pirin.

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arXiv2003

Fourier analysis of luminosity-dependent galaxy clustering

We extend the Fourier transform based method for the analysis of galaxy redshift surveys of Feldman, Kaiser & Peacock (1994: FKP) to model luminosity-dependent clustering. In a magnitude limited survey, galaxies at high redshift are more luminous on average than galaxies at low redshift. Galaxy clustering is observed to increase with luminosity, so the inferred density field is effectively multiplied by an increasing function of radius. This has the potential to distort the shape of the recovered power spectrum. In this paper we present an extension of the FKP analysis method to incorporate this effect, and present revised optimal weights to maximize the precision of such an analysis. The method is tested and its accuracy assessed using mock catalogues of the 2-degree field galaxy redshift survey (2dFGRS). We also show that the systematic effect caused by ignoring luminosity-dependent bias was negligible for the initial analysis of the 2dFGRS of Percival et al. (2001). However, future surveys, sensitive to larger scales, or covering a wider range of galaxy luminosities will benefit from this refined method.

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arXiv2003

The 2dF Galaxy Redshift Survey: Final Data Release

The 2dF Galaxy Redshift Survey (2dFGRS) has obtained spectra for 245591 sources, mainly galaxies, brighter than a nominal extinction-corrected magnitude limit of b_J=19.45. Reliable redshifts were measured for 221414 galaxies. The galaxies are selected from the extended APM Galaxy Survey and cover an area of approximately 1500 square degrees in three regions: an NGP strip, an SGP strip and random fields scattered around the SGP strip. This paper describes the 2dFGRS final data release of 30 June 2003 and complements Colless et al. (2001), which described the survey and the initial 100k data release. The 2dFGRS database and full documentation are available on the WWW at http://www.mso.anu.edu.au/2dFGRS/

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arXiv2002

The clustering of halo mergers

We analyse the spatial distribution of halo merger sites using four numerical simulations with high time resolution of structure growth in a Lambda-CDM cosmology. We find no evidence for any large-scale relative bias between mergers and randomly selected haloes of the same mass at high redshift. Given a sample of galaxies that form a Poisson sampling of halo mergers, then the amplitude of the measured clustering ought to lead to a robust estimate of the median host halo mass. In the hierarchical picture of structure growth, mergers between galaxies at high redshifts are thought to create dust enshrouded starbursts leading to increased emission in the sub-mm wavebands. Hence, a measurement of the clustering strength of SCUBA galaxies, for example, can determine whether or not they are giant elliptical galaxies in the process of formation.

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arXiv2002

Parameter constraints for flat cosmologies from CMB and 2dFGRS power spectra

We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega_m, which arises mainly from preserving the location of the peaks in the angular power spectrum. This `horizon-angle degeneracy' is considered in some detail and shown to follow a simple relation Omega_m h^{3.4} = constant. Adding the 2dFGRS power spectrum constrains Omega_m h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant h=0.665 +/- 0.047, the matter density Omega_m=0.313 +/- 0.055, and the physical CDM and baryon densities Omega_c h^2 = 0.115 +/- 0.009, Omega_b h^2 = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set a upper limit to the tensor-to-scalar ratio of r<0.7 at 95% confidence. We then show how these data can be used to constrain the equation of state of the vacuum, and find w<-0.52 at 95% confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/~wjp/

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arXiv2002

The 2dF Galaxy Redshift Survey: The amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear.

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arXiv2002

The 2dF Galaxy Redshift Survey: The Number and Luminosity Density of Galaxies

We present the bivariate brightness distribution (BBD) for the 2dF Galaxy Redshift Survey (2dFGRS) based on a preliminary subsample of 45,000 galaxies. The BBD is an extension of the galaxy luminosity function incorporating surface brightness information. It allows the measurement of the local luminosity density, j_B, and the galaxy luminosity and surface brightness distributions while accounting for surface brightness selection biases. The recovered 2dFGRS BBD shows a strong surface brightness-luminosity relation (M_B~2.4μ_e). The luminosity-density is dominated by normal galaxies and the luminosity-density peak lies away from the selection boundaries implying that the 2dFGRS is complete and that luminous low surface brightness galaxies are rare. The final value we derive for the local luminosity-density, inclusive of surface brightness corrections, is: j_B=2.49+/-0.20x10^8 h L_solar Mpc^-3. Representative Schechter function parameters are: M*=-19.75+/-0.05, phi*=2.02+/-0.02x10^-2 and alpha=-1.09+/-0.03. Extending the conventional methodology to incorporate surface brightness selection effects has resulted in an increase in the luminosity-density of 37%.

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arXiv2001

Evidence for a non-zero Lambda and a low matter density from a combined analysis of the 2dF Galaxy Redshift Survey and Cosmic Microwave Background Anisotropies

We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n_s and n_t. On its own, the 2dFGRS sets tight limits on the parameter combination Omega_m h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega_b/Omega_m. The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a `geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons and cold dark matter. Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a pm 2sigma range of 0.65 < Omega_Lambda < 0.85, completely independently of constraints on Omega_Λderived from Type Ia supernovae.

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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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arXiv1999

Overmerging and M/L ratios in phenomenological galaxy formation models

We show that the discrepancy between the Tully-Fisher relation and the luminosity function predicted by most phenomenological galaxy formation models is mainly due to overmerging of galaxy haloes. We have circumvented this overmerging problem, which is inherent in both the Press-Schechter formalism and dissipationless N-body simulations, by including a specific galaxy halo formation recipe into an otherwise standard N-body code. This numerical technique provides the merger trees which, together with simplified gas dynamics and star formation physics, constitute our implementation of a phenomenological galaxy formation model. Resolving the overmerging problem provides us with the means to match both the I-band Tully-Fisher relation and the B and K band luminosity functions within an EdS sCDM structure formation scenario. It also allows us to include models for chemical evolution and starbursts, which improves the match to observational data and renders the modelling more realistic. We show that the inclusion of chemical evolution into the modelling requires a significant fraction of stars to be formed in short bursts triggered by merging events.

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arXiv1998

Galaxy Clusters in the Hubble Volume Simulations

We report on analyses of cluster samples obtained from the Hubble Volume Simulations. These simulations, an $Ω=1$ model named $τ$CDM and a flat low $Ω$ model with a cosmological constant ($Λ$CDM), comprise the largest computational efforts to date in numerical cosmology. We investigate the presence of massive galaxy clusters at $z\approx 0.8$. The $τ$CDM model fails to form clusters at such a redshift. However, due to the small number of observed clusters around $z\approx 0.8$ and the uncertainties in the determinations of their masses, this conclusion still is somewhat preliminary. We produce cluster catalogs at $z=0$ for both cosmologies and investigate their two--point correlation function $ξ$. We show that the relationship between the mean density of subsamples of clusters, expressed via their mean separation $d_{\rm c}$, and the correlation length $r_0$, defined through $ξ(r_0) = 1$, is not linear but turns over gently for large $d_{\rm c}$. An analytic prediction by Mo & White (1996) overpredicts $r_0$. The results from the analysis of the APM cluster data by Croft et al. (1997) are nicely matched by the $Λ$CDM model.

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arXiv1993

Power Spectrum Analysis of Three-Dimensional Redshift Surveys

We develop a general method for power spectrum analysis of three dimensional redshift surveys. We present rigorous analytical estimates for the statistical uncertainty in the power and we are able to derive a rigorous optimal weighting scheme under the reasonable (and largely empirically verified) assumption that the long wavelength Fourier components are Gaussian distributed. We apply the formalism to the updated 1-in-6 QDOT IRAS redshift survey, and compare our results to data from other probes: APM angular correlations; the CfA and the Berkeley 1.2Jy IRAS redshift surveys. Our results bear out and further quantify the impression from e.g.\ counts-in-cells analysis that there is extra power on large scales as compared to the standard CDM model with $Ωh\simeq 0.5$. We apply likelihood analysis using the CDM spectrum with $Ωh$ as a free parameter as a phenomenological family of models; we find the best fitting parameters in redshift space and transform the results to real space. Finally, we calculate the distribution of the estimated long wavelength power. This agrees remarkably well with the exponential distribution expected for Gaussian fluctuations, even out to powers of ten times the mean. Our results thus reveal no trace of periodicity or other non-Gaussian behavior.

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