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Papers by Steve Maddox

The Astrophysical Journal, 1998

To derive a new Hα luminosity function and to understand the clustering properties of star-formin... more To derive a new Hα luminosity function and to understand the clustering properties of star-forming galaxies at z ≈ 0.24, we have made a narrow-band imaging survey for Hα emitting galaxies in the HST COSMOS 2 square degree field. We used the narrow-band filter NB816 (λ c = 8150Å, ∆λ = 120 A) and sampled Hα emitters with EW obs (Hα + [Nii]) > 12Å in a redshift range between z = 0.233 and z = 0.251 corresponding to a depth of 70 Mpc. We obtained 980 Hα emitting galaxies in a sky area of 5540 arcmin 2 , corresponding to a survey volume of 3.1 × 10 4 Mpc 3 . We derive a Hα luminosity function with a best-fit Schechter function parameter set of α = −1.35 +0.11 −0.13 , log φ * = −2.65 +0.27 −0.38 , and log L * (erg s −1 ) = 41.94 +0.38 −0.23 . The Hα luminosity density is 2.7 +0.7 −0.6 × 10 39 ergs s −1 Mpc −3 . After subtracting the AGN contribution (15 %) to the Hα luminosity density, the star formation rate density is evaluated as 1.8 +0.7 −0.4 × 10 −2 M ⊙ yr −1 Mpc −3 . The angular two-point correlation function of Hα emitting galaxies of log L(Hα) > 39.8 is well fit by a power law form of w(θ) = 0.013 +0.002 −0.001 θ −0.88±0.03 , corresponding to the correlation function of ξ(r) = (r/1.9Mpc) −1.88 . We also find that the Hα emitters with higher Hα luminosity are more strongly clustered than those with lower luminosity.

The Astronomical Journal, 2003

Existing observations are consistent with rich clusters of galaxies having no dust on > ∼ Mpc sca... more Existing observations are consistent with rich clusters of galaxies having no dust on > ∼ Mpc scales, while galaxy groups most probably do have dust distributed over Mpc scales. Dust in groups accounts for the observed redshift asymmetries of their galaxy distributions, and about E(B − V ) ∼ 0.1 − 0.2 mag of reddening. Motivated by these results, we develop a new technique for determining the degree of reddening and extinction due to widely-distributed dust in nearby moderately rich and poor galaxy clusters. The method compares the color-magnitude plane distributions of galaxies from cluster and control regions on the sky, where control regions are assumed to be unaffected by dust. The method is statistical in nature; it can distinguish between uniformly, nonuniformly, and clumpily distributed dust, and can determine the amount of reddening and obscuration without a priori assuming an A R /E(B J − R) ratio. We apply the method to nearby, z ≤ 0.08, medium rich and poor APM galaxy clusters. We detect no dust in these on 1.3 Mpc scales (we assume h = 0.75), and derive 99% confidence upper limits on extinction of A R = 0. m 025 and reddening of E(B J − R) = 0. m 025 (which corresponds to E(B − V ) ≈ 0. m 02). We test the method using clusters whose galaxies have been artificially reddened and obscured by various amounts, and conclude that it robustly recovers the input values for reddening, its distribution, and the ratio of total-to-selective extinction. The method can be applied to any set of galaxy clusters or groups constructed out of homogeneous and uniform two-color galaxy catalogs.

Nature, 2001

The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter ␤ ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.

Monthly Notices of the Royal Astronomical Society, 2002

We have cross-matched the 1.4 GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed i... more We have cross-matched the 1.4 GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 square degrees (about 20% of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio IDs -the largest and most homogeneous set of radio-source spectra ever obtained. The 2dFGRS radio sources span the redshift range z = 0.005 to 0.438, and are a mixture of active galaxies (60%) and star-forming galaxies (40%). About 25% of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We have made a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star-formation density of 0.022 ± 0.004 M ⊙ yr −1 Mpc −3 (H 0 =50 km s −1 Mpc −1 ).

Monthly Notices of the Royal Astronomical Society, 2004

We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG... more We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 28 877 groups with at least two members. The clustering amplitude of the full 2PIGG catalogue is weaker than that of 2dFGRS galaxies, in agreement with theoretical predictions. We have subdivided the 2PIGG catalogue into samples that span a factor of ≈ 25 in median total luminosity. Our correlation function measurements span an unprecedented range of clustering strengths, connecting the regimes probed by groups fainter than L * galaxies and rich clusters. There is a steady increase in clustering strength with group luminosity; the most luminous groups are ten times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the clustering of groups expected in the ΛCDM model.

Monthly Notices of the Royal Astronomical Society, 2004

We analyse the observed correlation between galaxy environment and Hα emission line strength, usi... more We analyse the observed correlation between galaxy environment and Hα emission line strength, using volume-limited samples and group catalogues of 24968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M bJ < −19.5) and the Sloan Digital Sky Survey (M r < −20.6). We characterise the environment by 1) Σ 5 , the surface number density of galaxies determined by the projected distance to the 5 th nearest neighbour; and 2) ρ 1.1 and ρ 5.5 , 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 Hα equivalent width, W 0 (Hα). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of W 0 (Hα) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, ρ 5.5 , which is likely independent of the trend with local density, ρ 1.1 . We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for σ = 200-1000 km s −1 . Even in the lowest density environments, no more than ∼ 70 per cent of galaxies show significant Hα 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.

Monthly Notices of The Royal Astronomical Society - MON NOTIC ROY ASTRON SOC, 2004

We present an analysis of the relative bias between early- and late-type galaxies in the Two-degr... more We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) - as defined by the η parameter of Madgwick et al., which quantifies the spectral type of galaxies in the survey. We calculate counts in cells for flux-limited samples of early- and late-type galaxies, using approximately cubical cells with sides ranging from 7 to 42 h-1 Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al., which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum-likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We then examine the joint density distribution function, f(δE, δL), and directly fit deterministic bias models to the joint counts in cells. We measure a linear relative bias of ~1.3, which does not vary significantly with l. A deterministic linear bias model is, however, a poor approximation to the data, especially on small scales (l<= 28h-1 Mpc) where deterministic linear bias is excluded at high significance. A power-law bias model with index b1~ 0.75 is a significantly better fit to the data on all scales, although linear bias becomes consistent with the data for l>~ 40h-1 Mpc.

Monthly Notices of The Royal Astronomical Society, 2000

We investigate the spatial clustering of galaxies in the PSCz galaxy redshift survey, as revealed... more We investigate the spatial clustering of galaxies in the PSCz galaxy redshift survey, as revealed by the two-point correlation function, the luminosity mark correlations, and the moments of counts-in-cells. We construct volume-limited subsamples at different depths, and search for a luminosity dependence of the clustering pattern. We find no statistically significant effect in either the two-point correlation function or the mark correlations and so we take each subsample (of different characteristic luminosity) as representing the same statistical process. We then carry out a counts-in-cells analysis of the volume-limited subsamples, including a rigorous error calculation based on the recent theory of Szapudi, Colombi and Bernardeau. In this way, we derive the best estimates to date of the skewness and kurtosis of IRAS galaxies in redshift space. Our results agree well with previous measurements in both the parent angular catalogue, and in the derived redshift surveys. This is in contrast with smaller, optically selected surveys, were there is a discrepancy between the redshift space and projected measurements. Predictions from cold dark matter theory, obtained using the recent semi-analytical model of galaxy formation of Benson {\it et al}, provide an excellent description of our clustering data.

The Astrophysical Journal, 2002

We present the first results on the history of star formation in the Universe based on the 'cosmi... more We present the first results on the history of star formation in the Universe based on the 'cosmic spectrum', in particular, the volume-averaged, luminosity-weighted, stellar absorption line spectrum of present day galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that unlike previous studies it is not an estimator based on total luminosity density. The cosmic spectrum is fitted with models of population synthesis, tracing the history of star formation prior to the epoch of the observed galaxies, using a method we have developed which decouples continuum and spectral-line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with models incorporating chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value and that the increase back to z = 1, assuming it scales as (1 + z) β , has a strong upper limit of β < 5. We find in the general case there is some model degeneracy between star formation at low and high redshift. However, if we incorporate previous work on star formation at z < 1 we can put strong upper limits on the star-formation rate at z > 1: e.g., if β > 2 then the SFR for 1 < z < 5 scales as (1 + z) α with α < 2. This is equivalent to stating that no more than 80% of stars in the Universe formed at z > 1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density, which give 1.8 < β < 2.9 and −1.0 < α < 0.7, and are also consistent with estimates of Ω stars based on the K-band luminosity density.

The Astrophysical Journal, 2003

In the course of a weak gravitational lensing survey of 39 clusters of galaxies, covering a total... more In the course of a weak gravitational lensing survey of 39 clusters of galaxies, covering a total sky area of ∼ 1 square degree, we have serendipitously discovered mass concentrations in the fields of A1705 and A1722 which are most probably not associated with the main cluster target. By combining weak lensing information with two-color galaxy photometry in fields centered on our sample clusters, we identify a new cluster candidate at z ∼ 0.5 in the field of A1705. This cluster candidate also displays strong lensing in the form of a giant luminous arc. The new mass concentration in the field of A1722 also seems to be associated with an optically luminous cluster of galaxies at z ∼ 0.5, but in this case there is some evidence for additional structures along the line of sight that may contribute to the lensing signal. A third cluster, A959, has a dark sub-clump which shows interesting morphological evidence in the mass map for being associated with the main cluster. This is the first case where there is any significant evidence for a physical association between a dark sub-clump (discovered from weak lensing) and a normal cluster. Analysis of archival X-ray data shows that the three new mass concentrations are not firmly detected in X-rays and that they are X-ray underluminous.

Monthly Notices of the Royal Astronomical Society, 2004

Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure ... more 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).

Monthly Notices of the Royal Astronomical Society, 2004

The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (... more The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS) is described. Groups are identified by means of a friends-offriends percolation algorithm which has been thoroughly tested on mock versions of the 2dFGRS generated from cosmological N-body simulations. The tests suggest that the algorithm groups all galaxies that it should be grouping, with an additional 40 per cent of interlopers. About 55 per cent of the ∼ 190 000 galaxies considered are placed into groups containing at least two members of which ∼ 29 000 are found. Of these, ∼ 7000 contain at least four galaxies, and these groups have a median redshift of 0.11 and a median velocity dispersion of 260 km s −1 . This 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue represents the largest available homogeneous sample of galaxy groups. It is publicly available on the WWW.

Monthly Notices of the Royal Astronomical Society, 2005

We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct ... more We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct Fourier method. The sample used comprises 221 414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models, and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the 'baryon oscillations' that are predicted in CDM models. Fitting to a CDM model, assuming a primordial n s = 1 spectrum, h = 0.72 and negligible neutrino mass, the preferred parameters are Ω m h = 0.168 ± 0.016 and a baryon fraction Ω b /Ω m = 0.185 ± 0.046 (1σ errors). The value of Ω m h is 1σ lower than the 0.20 ± 0.03 in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly-sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard Ω m = 0.3: in combination with CMB data from WMAP, we infer Ω m = 0.231 ± 0.021.

Monthly Notices of the Royal Astronomical Society, 2005

We present an analysis of the relative bias between early-and late-type galaxies in the Two-degre... more We present an analysis of the relative bias between early-and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) -as defined by the η parameter of , which quantifies the spectral type of galaxies in the survey. Our analysis examines the joint counts in cells between early-and late-type galaxies, using approximately cubical cells with sides ranging from 7h −1 Mpc to 42h −1 Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al. (1990), which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We use a modified χ 2 technique to determine to what extent the relative bias is consistent with a simple linear bias relation; this analysis results in a significant detection of nonlinearity/stochasticity even on large scales. We directly fit deterministic models for the joint density distribution function, f (δ E , δ L ), to the joint counts in cells using a maximum likelihood technique. Our results are consistent with a scale invariant relative bias factor on all scales studied. Linear bias is ruled out on scales less than ℓ = 28h −1 Mpc. A power-law bias model is a significantly better fit to the data on all but the largest scales studied; the relative goodness of fit of this model as compared to that of the linear bias model suggests that any nonlinearity is negligible for ℓ 40h −1 Mpc, consistent with the expectation from theory that the bias should become linear on large scales.

Monthly Notices of the Royal Astronomical Society, 2004

We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonorm... more 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 Ω 0.6 m σ 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 β(L * , 0) = 0.58 ± 0.08, and the amplitude of the overdensity fluctuations b(L * , 0)σ 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.

Monthly Notices of the Royal Astronomical Society, 2004

We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field... more We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.

Monthly Notices of the Royal Astronomical Society, 2004

The clustering properties of local, S 1.4GHz ≥ 1 mJy, radio sources are investigated for a sample... more The clustering properties of local, S 1.4GHz ≥ 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 b J ≤ 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. From measurements of the redshift-space correlation function ξ(s) we derive a redshift-space clustering length s 0 = 10.7 +0.8 −0.7 Mpc, while from the projected correlation function Ξ(r T ) we estimate the parameters of the real-space correlation function ξ(r) = (r/r 0 ) −γ , r 0 = 6.7 +0.9 −1.1 Mpc and γ = 1.6 ± 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 ± 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. Comparisons with models for ξ(r) show that AGN-fuelled sources reside in dark matter halos more massive than ∼ 10 13.4 M ⊙ , 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 min BH ∼ 10 9 M ⊙ . 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.

Monthly Notices of the Royal Astronomical Society, 2003

We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosit... more We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h −1 Mpc, 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 − 5 log 10 h < ∼ − 18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M bJ − 5 log 10 h < ∼ − 21. Differences in the mid to faint-end population between environments are significant: at M bJ − 5 log 10 h = −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.

Monthly Notices of the Royal Astronomical Society, 2001

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using ... more We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power-law in pair separation over the range 0.1 < (r/ h −1 Mpc) < 10. The clustering of L * (M bJ − 5 log 10 h = −19.7) galaxies in real space is well fit by a correlation length r 0 = 4.9 ± 0.3 h −1 Mpc and power-law slope γ = 1.71 ± 0.06. The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M * , but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the SSRS2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between M bJ − 5 log 10 h = −18 and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.

Monthly Notices of the Royal Astronomical Society, 2002

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V 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 scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. 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 Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.

The Astrophysical Journal, 1998

To derive a new Hα luminosity function and to understand the clustering properties of star-formin... more To derive a new Hα luminosity function and to understand the clustering properties of star-forming galaxies at z ≈ 0.24, we have made a narrow-band imaging survey for Hα emitting galaxies in the HST COSMOS 2 square degree field. We used the narrow-band filter NB816 (λ c = 8150Å, ∆λ = 120 A) and sampled Hα emitters with EW obs (Hα + [Nii]) > 12Å in a redshift range between z = 0.233 and z = 0.251 corresponding to a depth of 70 Mpc. We obtained 980 Hα emitting galaxies in a sky area of 5540 arcmin 2 , corresponding to a survey volume of 3.1 × 10 4 Mpc 3 . We derive a Hα luminosity function with a best-fit Schechter function parameter set of α = −1.35 +0.11 −0.13 , log φ * = −2.65 +0.27 −0.38 , and log L * (erg s −1 ) = 41.94 +0.38 −0.23 . The Hα luminosity density is 2.7 +0.7 −0.6 × 10 39 ergs s −1 Mpc −3 . After subtracting the AGN contribution (15 %) to the Hα luminosity density, the star formation rate density is evaluated as 1.8 +0.7 −0.4 × 10 −2 M ⊙ yr −1 Mpc −3 . The angular two-point correlation function of Hα emitting galaxies of log L(Hα) > 39.8 is well fit by a power law form of w(θ) = 0.013 +0.002 −0.001 θ −0.88±0.03 , corresponding to the correlation function of ξ(r) = (r/1.9Mpc) −1.88 . We also find that the Hα emitters with higher Hα luminosity are more strongly clustered than those with lower luminosity.

The Astronomical Journal, 2003

Existing observations are consistent with rich clusters of galaxies having no dust on > ∼ Mpc sca... more Existing observations are consistent with rich clusters of galaxies having no dust on > ∼ Mpc scales, while galaxy groups most probably do have dust distributed over Mpc scales. Dust in groups accounts for the observed redshift asymmetries of their galaxy distributions, and about E(B − V ) ∼ 0.1 − 0.2 mag of reddening. Motivated by these results, we develop a new technique for determining the degree of reddening and extinction due to widely-distributed dust in nearby moderately rich and poor galaxy clusters. The method compares the color-magnitude plane distributions of galaxies from cluster and control regions on the sky, where control regions are assumed to be unaffected by dust. The method is statistical in nature; it can distinguish between uniformly, nonuniformly, and clumpily distributed dust, and can determine the amount of reddening and obscuration without a priori assuming an A R /E(B J − R) ratio. We apply the method to nearby, z ≤ 0.08, medium rich and poor APM galaxy clusters. We detect no dust in these on 1.3 Mpc scales (we assume h = 0.75), and derive 99% confidence upper limits on extinction of A R = 0. m 025 and reddening of E(B J − R) = 0. m 025 (which corresponds to E(B − V ) ≈ 0. m 02). We test the method using clusters whose galaxies have been artificially reddened and obscured by various amounts, and conclude that it robustly recovers the input values for reddening, its distribution, and the ratio of total-to-selective extinction. The method can be applied to any set of galaxy clusters or groups constructed out of homogeneous and uniform two-color galaxy catalogs.

Nature, 2001

The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter ␤ ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.

Monthly Notices of the Royal Astronomical Society, 2002

We have cross-matched the 1.4 GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed i... more We have cross-matched the 1.4 GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 square degrees (about 20% of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio IDs -the largest and most homogeneous set of radio-source spectra ever obtained. The 2dFGRS radio sources span the redshift range z = 0.005 to 0.438, and are a mixture of active galaxies (60%) and star-forming galaxies (40%). About 25% of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We have made a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star-formation density of 0.022 ± 0.004 M ⊙ yr −1 Mpc −3 (H 0 =50 km s −1 Mpc −1 ).

Monthly Notices of the Royal Astronomical Society, 2004

We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG... more We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 28 877 groups with at least two members. The clustering amplitude of the full 2PIGG catalogue is weaker than that of 2dFGRS galaxies, in agreement with theoretical predictions. We have subdivided the 2PIGG catalogue into samples that span a factor of ≈ 25 in median total luminosity. Our correlation function measurements span an unprecedented range of clustering strengths, connecting the regimes probed by groups fainter than L * galaxies and rich clusters. There is a steady increase in clustering strength with group luminosity; the most luminous groups are ten times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the clustering of groups expected in the ΛCDM model.

Monthly Notices of the Royal Astronomical Society, 2004

We analyse the observed correlation between galaxy environment and Hα emission line strength, usi... more We analyse the observed correlation between galaxy environment and Hα emission line strength, using volume-limited samples and group catalogues of 24968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M bJ < −19.5) and the Sloan Digital Sky Survey (M r < −20.6). We characterise the environment by 1) Σ 5 , the surface number density of galaxies determined by the projected distance to the 5 th nearest neighbour; and 2) ρ 1.1 and ρ 5.5 , 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 Hα equivalent width, W 0 (Hα). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of W 0 (Hα) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, ρ 5.5 , which is likely independent of the trend with local density, ρ 1.1 . We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for σ = 200-1000 km s −1 . Even in the lowest density environments, no more than ∼ 70 per cent of galaxies show significant Hα 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.

Monthly Notices of The Royal Astronomical Society - MON NOTIC ROY ASTRON SOC, 2004

We present an analysis of the relative bias between early- and late-type galaxies in the Two-degr... more We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) - as defined by the η parameter of Madgwick et al., which quantifies the spectral type of galaxies in the survey. We calculate counts in cells for flux-limited samples of early- and late-type galaxies, using approximately cubical cells with sides ranging from 7 to 42 h-1 Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al., which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum-likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We then examine the joint density distribution function, f(δE, δL), and directly fit deterministic bias models to the joint counts in cells. We measure a linear relative bias of ~1.3, which does not vary significantly with l. A deterministic linear bias model is, however, a poor approximation to the data, especially on small scales (l<= 28h-1 Mpc) where deterministic linear bias is excluded at high significance. A power-law bias model with index b1~ 0.75 is a significantly better fit to the data on all scales, although linear bias becomes consistent with the data for l>~ 40h-1 Mpc.

Monthly Notices of The Royal Astronomical Society, 2000

We investigate the spatial clustering of galaxies in the PSCz galaxy redshift survey, as revealed... more We investigate the spatial clustering of galaxies in the PSCz galaxy redshift survey, as revealed by the two-point correlation function, the luminosity mark correlations, and the moments of counts-in-cells. We construct volume-limited subsamples at different depths, and search for a luminosity dependence of the clustering pattern. We find no statistically significant effect in either the two-point correlation function or the mark correlations and so we take each subsample (of different characteristic luminosity) as representing the same statistical process. We then carry out a counts-in-cells analysis of the volume-limited subsamples, including a rigorous error calculation based on the recent theory of Szapudi, Colombi and Bernardeau. In this way, we derive the best estimates to date of the skewness and kurtosis of IRAS galaxies in redshift space. Our results agree well with previous measurements in both the parent angular catalogue, and in the derived redshift surveys. This is in contrast with smaller, optically selected surveys, were there is a discrepancy between the redshift space and projected measurements. Predictions from cold dark matter theory, obtained using the recent semi-analytical model of galaxy formation of Benson {\it et al}, provide an excellent description of our clustering data.

The Astrophysical Journal, 2002

We present the first results on the history of star formation in the Universe based on the 'cosmi... more We present the first results on the history of star formation in the Universe based on the 'cosmic spectrum', in particular, the volume-averaged, luminosity-weighted, stellar absorption line spectrum of present day galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that unlike previous studies it is not an estimator based on total luminosity density. The cosmic spectrum is fitted with models of population synthesis, tracing the history of star formation prior to the epoch of the observed galaxies, using a method we have developed which decouples continuum and spectral-line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with models incorporating chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value and that the increase back to z = 1, assuming it scales as (1 + z) β , has a strong upper limit of β < 5. We find in the general case there is some model degeneracy between star formation at low and high redshift. However, if we incorporate previous work on star formation at z < 1 we can put strong upper limits on the star-formation rate at z > 1: e.g., if β > 2 then the SFR for 1 < z < 5 scales as (1 + z) α with α < 2. This is equivalent to stating that no more than 80% of stars in the Universe formed at z > 1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density, which give 1.8 < β < 2.9 and −1.0 < α < 0.7, and are also consistent with estimates of Ω stars based on the K-band luminosity density.

The Astrophysical Journal, 2003

In the course of a weak gravitational lensing survey of 39 clusters of galaxies, covering a total... more In the course of a weak gravitational lensing survey of 39 clusters of galaxies, covering a total sky area of ∼ 1 square degree, we have serendipitously discovered mass concentrations in the fields of A1705 and A1722 which are most probably not associated with the main cluster target. By combining weak lensing information with two-color galaxy photometry in fields centered on our sample clusters, we identify a new cluster candidate at z ∼ 0.5 in the field of A1705. This cluster candidate also displays strong lensing in the form of a giant luminous arc. The new mass concentration in the field of A1722 also seems to be associated with an optically luminous cluster of galaxies at z ∼ 0.5, but in this case there is some evidence for additional structures along the line of sight that may contribute to the lensing signal. A third cluster, A959, has a dark sub-clump which shows interesting morphological evidence in the mass map for being associated with the main cluster. This is the first case where there is any significant evidence for a physical association between a dark sub-clump (discovered from weak lensing) and a normal cluster. Analysis of archival X-ray data shows that the three new mass concentrations are not firmly detected in X-rays and that they are X-ray underluminous.

Monthly Notices of the Royal Astronomical Society, 2004

Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure ... more 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).

Monthly Notices of the Royal Astronomical Society, 2004

The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (... more The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS) is described. Groups are identified by means of a friends-offriends percolation algorithm which has been thoroughly tested on mock versions of the 2dFGRS generated from cosmological N-body simulations. The tests suggest that the algorithm groups all galaxies that it should be grouping, with an additional 40 per cent of interlopers. About 55 per cent of the ∼ 190 000 galaxies considered are placed into groups containing at least two members of which ∼ 29 000 are found. Of these, ∼ 7000 contain at least four galaxies, and these groups have a median redshift of 0.11 and a median velocity dispersion of 260 km s −1 . This 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue represents the largest available homogeneous sample of galaxy groups. It is publicly available on the WWW.

Monthly Notices of the Royal Astronomical Society, 2005

We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct ... more We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct Fourier method. The sample used comprises 221 414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models, and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the 'baryon oscillations' that are predicted in CDM models. Fitting to a CDM model, assuming a primordial n s = 1 spectrum, h = 0.72 and negligible neutrino mass, the preferred parameters are Ω m h = 0.168 ± 0.016 and a baryon fraction Ω b /Ω m = 0.185 ± 0.046 (1σ errors). The value of Ω m h is 1σ lower than the 0.20 ± 0.03 in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly-sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard Ω m = 0.3: in combination with CMB data from WMAP, we infer Ω m = 0.231 ± 0.021.

Monthly Notices of the Royal Astronomical Society, 2005

We present an analysis of the relative bias between early-and late-type galaxies in the Two-degre... more We present an analysis of the relative bias between early-and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) -as defined by the η parameter of , which quantifies the spectral type of galaxies in the survey. Our analysis examines the joint counts in cells between early-and late-type galaxies, using approximately cubical cells with sides ranging from 7h −1 Mpc to 42h −1 Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al. (1990), which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We use a modified χ 2 technique to determine to what extent the relative bias is consistent with a simple linear bias relation; this analysis results in a significant detection of nonlinearity/stochasticity even on large scales. We directly fit deterministic models for the joint density distribution function, f (δ E , δ L ), to the joint counts in cells using a maximum likelihood technique. Our results are consistent with a scale invariant relative bias factor on all scales studied. Linear bias is ruled out on scales less than ℓ = 28h −1 Mpc. A power-law bias model is a significantly better fit to the data on all but the largest scales studied; the relative goodness of fit of this model as compared to that of the linear bias model suggests that any nonlinearity is negligible for ℓ 40h −1 Mpc, consistent with the expectation from theory that the bias should become linear on large scales.

Monthly Notices of the Royal Astronomical Society, 2004

We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonorm... more 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 Ω 0.6 m σ 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 β(L * , 0) = 0.58 ± 0.08, and the amplitude of the overdensity fluctuations b(L * , 0)σ 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.

Monthly Notices of the Royal Astronomical Society, 2004

We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field... more We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.

Monthly Notices of the Royal Astronomical Society, 2004

The clustering properties of local, S 1.4GHz ≥ 1 mJy, radio sources are investigated for a sample... more The clustering properties of local, S 1.4GHz ≥ 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 b J ≤ 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. From measurements of the redshift-space correlation function ξ(s) we derive a redshift-space clustering length s 0 = 10.7 +0.8 −0.7 Mpc, while from the projected correlation function Ξ(r T ) we estimate the parameters of the real-space correlation function ξ(r) = (r/r 0 ) −γ , r 0 = 6.7 +0.9 −1.1 Mpc and γ = 1.6 ± 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 ± 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. Comparisons with models for ξ(r) show that AGN-fuelled sources reside in dark matter halos more massive than ∼ 10 13.4 M ⊙ , 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 min BH ∼ 10 9 M ⊙ . 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.

Monthly Notices of the Royal Astronomical Society, 2003

We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosit... more We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h −1 Mpc, 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 − 5 log 10 h < ∼ − 18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M bJ − 5 log 10 h < ∼ − 21. Differences in the mid to faint-end population between environments are significant: at M bJ − 5 log 10 h = −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.

Monthly Notices of the Royal Astronomical Society, 2001

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using ... more We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power-law in pair separation over the range 0.1 < (r/ h −1 Mpc) < 10. The clustering of L * (M bJ − 5 log 10 h = −19.7) galaxies in real space is well fit by a correlation length r 0 = 4.9 ± 0.3 h −1 Mpc and power-law slope γ = 1.71 ± 0.06. The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M * , but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the SSRS2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between M bJ − 5 log 10 h = −18 and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.

Monthly Notices of the Royal Astronomical Society, 2002

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V 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 scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. 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 Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.