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We present an analysis of a sample of robust high-redshift galaxies selected from the 'blank' fields of the Prime Extragalactic Areas for Reionization Science (PEARLS) survey and Early Release Observations (ERO) data from JWST with the aim of selecting candidate high-redshift active galactic nuclei (AGN). Sources were identified from this parent sample using a threefold selection procedure, which includes spectral energy distribution (SED) fitting to identify sources that are best fitted by AGN SED templates, a further selection based on the relative performance of AGN and non-AGN models, and finally morphological fitting to identify compact sources of emission, resulting in a purity-oriented procedure. Using this procedure, we identify a sample of nine AGN candidates at 6.5 < z < 12, from which we constrain their physical properties as well as measure a lower bound on the AGN fraction in this redshift range of 5 ± 1 per cent. As this is an extreme lower limit due to our focus on purity and our SEDs being calibrated for unobscured Type 1 AGN, this demonstrates that AGN are perhaps quite common at this early epoch. The rest-frame UV colours of our candidate objects suggest that these systems are potentially candidate obese black hole galaxies (OBGs). We also investigate Chandra and VLA maps of these areas from which we calculate detection limits. Of note is a z  = 11.9 candidate source exhibiting an abrupt morphological shift in the reddest band as compared to bluer bands, indicating a potential merger or an unusually strong outflow. [ABSTRACT FROM AUTHOR]

We derive single Sérsic fits and bulge-disc decompositions for 13 096 galaxies at redshifts z < 0.08 in the GAMA II equatorial survey regions in the Kilo-Degree Survey (KiDS) g, r , and i bands. The surface brightness fitting is performed using the Bayesian two-dimensional profile fitting code ProFit. We fit three models to each galaxy in each band independently with a fully automated Markov chain Monte Carlo analysis: a single Sérsic model, a Sérsic plus exponential and a point source plus exponential. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate (mainly mergers/Irregular galaxies). The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2–3. Automated model selection criteria are accurate to |$\gt 90{{\ \rm per\ cent}}$| as calibrated by visual inspection of a subsample of galaxies. We also present g − r component colours and the corresponding colour–magnitude diagram, consistent with previous works despite our increased fit flexibility. Such reliable structural parameters for the components of a diverse sample of galaxies across multiple bands will be integral to various studies of galaxy properties and evolution. All results are integrated into the GAMA database. [ABSTRACT FROM AUTHOR]

We investigate changes in stellar population age and metallicity ([Z/H]) scaling relations for quiescent galaxies from intermediate redshift (0.60 ≤   |$z$| ≤ 0.76) using the LEGA-C Survey to low redshift (0.014 ≤   |$z$| ≤ 0.10) using the SAMI Galaxy Survey. Specifically, we study how the spatially integrated global age and metallicity of individual quiescent galaxies vary in the mass–size plane, using the stellar mass M * and a dynamical mass proxy derived from the virial theorem M D  ∝ σ2  R e. We find that, similarly to at low redshift, the metallicity of quiescent galaxies at 0.60 ≤   |$z$| ≤ 0.76 closely correlates with M / R e (a proxy for the gravitational potential or escape velocity), in that galaxies with deeper potential wells are more metal-rich. This supports the hypothesis that the relation arises due to the gravitational potential regulating the retention of metals by determining the escape velocity for metal-rich stellar and supernova ejecta to escape the system and avoid being recycled into later stellar generations. Conversely, we find no correlation between age and surface density (⁠|$M/R_\mathrm{e}^2$|⁠) at 0.60 ≤   |$z$| ≤ 0.76, despite this relation being strong at low redshift. We consider this change in the age– |$M/R_\mathrm{e}^2$| relation in the context of the redshift evolution of the star-forming and quiescent mass–size relations, and find our results are consistent with galaxies forming more compactly at higher redshifts and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift. The |$z$| ∼  0 age– |$M/R_\mathrm{e}^2$| relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and therefore a range of surface densities. [ABSTRACT FROM AUTHOR]

The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming 'main sequence' and a separate region of 'passive' or 'red-and-dead' galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red starforming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population. [ABSTRACT FROM AUTHOR]

With a large sample of bright, low-redshift galaxies with optical-near-IR imaging from the GAMA survey we use bulge-disc decompositions to understand the wavelength-dependent behaviour of single-Sérsic structural measurements. We denote the variation in single-Sérsic index with wavelength asN, likewise for effective radius we use R. We find that most galaxies with a substantial disc, even those with no discernable bulge, display a high value of N. The increase in Sérsic index to longer wavelengths is therefore intrinsic to discs, apparently resulting from radial variations in stellar population and/or dust reddening. Similarly, low values of R (< 1) are found to be ubiquitous, implying an element of universality in galaxy colour gradients. We also study how bulge and disc colour distributions vary with galaxy type. We find that, rather than all bulges being red and all discs being blue in absolute terms, both components become redder for galaxies with redder total colours. We even observe that bulges in bluer galaxies are typically bluer than discs in red galaxies, and that bulges and discs are closer in colour for fainter galaxies. Trends in total colour are therefore not solely due to the colour or flux dominance of the bulge or disc. [ABSTRACT FROM AUTHOR]

We study the stellar-to-halo mass relation of central galaxies in the range 9.7 < log10(M*/h-2M☉) < 11.7 and z < 0.4, obtained from a combined analysis of the Kilo Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. We use ∼100 deg2 of KiDS data to study the lensing signal around galaxies for which spectroscopic redshifts and stellar masses were determined by GAMA.We show that lensing alone results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when we simultaneously fit the stellar mass function. At M* > 5 × 1010 h-2M☉, the stellar mass increases with halo mass as ∼M0.25h. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8 × 1011 h-1M ☉with a value of Mh/M* = 56+16-10 [h].We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper describes the first catalogue of photometrically derived stellar mass estimates for intermediate-redshift ( z < 0.65; median z= 0.2) galaxies in the Galaxy And Mass Assembly (GAMA) spectroscopic redshift survey. These masses, as well as the full set of ancillary stellar population parameters, will be made public as part of GAMA data release 2. Although the GAMA database does include near-infrared (NIR) photometry, we show that the quality of our stellar population synthesis fits is significantly poorer when these NIR data are included. Further, for a large fraction of galaxies, the stellar population parameters inferred from the optical-plus-NIR photometry are formally inconsistent with those inferred from the optical data alone. This may indicate problems in our stellar population library, or NIR data issues, or both; these issues will be addressed for future versions of the catalogue. For now, we have chosen to base our stellar mass estimates on optical photometry only. In light of our decision to ignore the available NIR data, we examine how well stellar mass can be constrained based on optical data alone. We use generic properties of stellar population synthesis models to demonstrate that restframe colour alone is in principle a very good estimator of stellar mass-to-light ratio, M*/ Li. Further, we use the observed relation between restframe ( g− i) and M*/ Li for real GAMA galaxies to argue that, modulo uncertainties in the stellar evolution models themselves, ( g− i) colour can in practice be used to estimate M*/ Li to an accuracy of ≲0.1 dex (1σ). This 'empirically calibrated' ( g− i)- M*/ Li relation offers a simple and transparent means for estimating galaxies' stellar masses based on minimal data, and so provides a solid basis for other surveys to compare their results to z≲0.4 measurements from GAMA. [ABSTRACT FROM AUTHOR]

We combine data from the Millennium Galaxy Catalogue, Sloan Digital Sky Survey and UKIRT Infrared Deep Sky Survey Large Area Survey to produce ugrizYJHK luminosity functions and densities from within a common, low-redshift volume ( for systems) with 100 per cent spectroscopic completeness. In the optical the fitted Schechter functions are comparable in shape to those previously reported values but with higher normalizations (typically 0, 30, 20, 15, 5 per cent higher values in , respectively, over those reported by the SDSS team). We attribute these to differences in the redshift ranges probed, incompleteness and adopted normalization methods. In the near-IR (NIR) we find significantly different Schechter function parameters (mainly in the values) to those previously reported and attribute this to the improvement in the quality of the imaging data over previous studies. This is the first homogeneous measurement of the extragalactic luminosity density which fully samples both the optical and NIR regimes. Unlike previous compilations that have noted a discontinuity between the optical and NIR regimes our homogeneous data set shows a smooth cosmic spectral energy distribution (CSED). After correcting for dust attenuation we compare our CSED to the expected values based on recent constraints on the cosmic star formation history and the initial mass function. [ABSTRACT FROM AUTHOR]

Simon P Driver, Peder Norberg, Ivan K Baldry, Steven P Bamford, Andrew M Hopkins, Jochen Liske, Jon Loveday, John A Peacock and the GAMA Survey Team (Galaxy and Mass Assembly) review progress on the latest large galaxy redshift survey now underway on the 3.9 m Anglo-Australian Telescope. [ABSTRACT FROM AUTHOR]

We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and [O ii] (3727 Å) lines and the D4000 index. LRGs are luminous galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and [O ii] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O ii] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario. [ABSTRACT FROM AUTHOR]

We present a spectroscopic survey of almost 15 000 candidate intermediate-redshift luminous red galaxies (LRGs) brighter than , observed with 2dF on the Anglo-Australian Telescope. The targets were selected photometrically from the Sloan Digital Sky Survey (SDSS) and lie along two narrow equatorial strips covering 180 deg2. Reliable redshifts were obtained for 92 per cent of the targets and the selection is very efficient: over 90 per cent have . More than 80 per cent of the red galaxies have pure absorption-line spectra consistent with a passively evolving old stellar population. The redshift, photometric and spatial distributions of the LRGs are described. The 2SLAQ data will be released publicly from mid-2006, providing a powerful resource for observational cosmology and the study of galaxy evolution. [ABSTRACT FROM AUTHOR]

We use deep wide-field V-band imaging obtained with the Wide Field Camera at the prime focus of the Issac Newton Telescope to study the spatial and luminosity distribution of galaxies in three low redshift (0.04 < z < 0.2) clusters: Abell 119, Abell 2443 and Abell 2218. The absolute magnitude limits probed in these clusters are , respectively. The galaxy population, at all luminosities, along the line-of-sight to the clusters can be described by the linear combination of a King profile and a constant surface density of field galaxies. We find that, for these three clusters, the core radius is invariant with intrinsic luminosity of the cluster population to the above limits and thus there is no evidence for luminosity segregation in these clusters. The exception is the brightest galaxies in A2218 which exhibit a more compact spatial distribution. We find that the total projected luminosity distribution (within of the cluster centre) can be well represented by a single Schechter function with moderately flat faint-end slopes: (A119), (A2443) and (A2218). We perform a geometric deprojection of the cluster galaxy population and confirm that no ‘statistically significant’ evidence of a change in the shape of the luminosity distribution with cluster-centric radius exists. Again, the exception being A2218 which exhibits a core region with a flatter faint-end slope. [ABSTRACT FROM AUTHOR]

We present a power-spectrum analysis of the final 2dF Galaxy Redshift Survey (2dFGRS), 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 cold dark matter (CDM) models. Fitting to a CDM model, assuming a primordial spectrum, and negligible neutrino mass, the preferred parameters are and a baryon fraction (1σ errors). The value of is 1σ lower than the 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 : in combination with cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe ( WMAP), we infer . [ABSTRACT FROM AUTHOR]

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 theη 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. 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,, 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 withℓ. A deterministic linear bias model is, however, a poor approximation to the data, especially on small scaleswhere deterministic linear bias is excluded at high significance. A power-law bias model with indexis a significantly better fit to the data on all scales, although linear bias becomes consistent with the data for. [ABSTRACT FROM AUTHOR]

It is well known that the clustering of galaxies depends on galaxy type. Suchrelative biascomplicates 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,η, 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 non-linearity and stochasticity of the relative bias, with cubic cells of side. 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 (rLN) of 0.958 for cells of length, increasing to 0.970 by. This corresponds to a stochasticityofand, 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 semi-analytic galaxy formation models: these match the data well in terms of the overall level of stochasticity, variation with scale and the fraction of empty cells. [ABSTRACT FROM AUTHOR]

ABSTRACT The Two-degree Field Galaxy Redshift Survey (2dFGRS) Percolation-Inferred Galaxy Group (2PIGG) catalogue of ∼29 000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. It is found that a Schechter function is a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, and that the characteristic luminosity L⋆ is slightly larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. Luminosity function results are presented in both the bJ and rF wavebands. The variation of the halo mass-to-light ratio, ϒ, with group size is studied in both of these wavebands. A robust trend of increasing ϒ with increasing group luminosity is found in the 2PIGG data. Going from groups with bJ luminosities equal to 1010 h−2 L⊙ to those 100 times more luminous, the typical bJ-band mass-to-light ratio increases by a factor of 5, whereas the rF-band mass-to-light ratio grows by a factor of 3.5. These trends agree well with the predictions of the simulations which also predict a minimum in the mass-to-light ratio on a scale roughly corresponding to the Local Group. The data indicate that if such a minimum exists, then it must occur at L≲ 1010 h−2 L⊙, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bJ mass-to-light ratios of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data, the mean bJ luminosity density of the Universe yields an estimate of Ωm= 0.26 ± 0.03 (statistical error only). Various possible sources of systematic error are considered, with the conclusion that these could affect the estimate of Ωm by a few tens of per cent. [ABSTRACT FROM AUTHOR]

ABSTRACT We select a sample of low-redshift ( z∼ 0.1) E+A galaxies from the 2dF Galaxy Redshift Survey (2dFGRS). The spectra of these objects are defined by strong hydrogen Balmer absorption lines (Hδ, Hγ, Hβ) combined with a lack of [O ii] 3727-Å emission, together implying a recently truncated burst of star formation. The E+A spectrum is thus a signpost to galaxies in the process of evolution. We quantify the local environments, clustering properties and luminosity function of the E+A galaxies. We find that the environments are consistent with the ensemble of 2dFGRS galaxies: low-redshift E+A systems are located predominantly in the field, existing as isolated objects or in poor groups. However, the luminosity distribution of galaxies selected using three Balmer absorption lines Hδγβ appears more typical of ellipticals. Indeed, morphologically these galaxies are preferentially spheroidal (E/S0) systems. In a small but significant number we find evidence for recent major mergers, such as tidal tails. We infer that major mergers are one important formation mechanism for E+A galaxies, as suggested by previous studies. At low redshift the merger probability is high in the field and low in clusters, thus these recently formed spheroidal systems do not follow the usual morphology-density relation for ellipticals. Regarding the selection of E+A galaxies: we find that basing the Balmer-line criterion solely on Hδ absorption leads to a significant subpopulation of disc systems with detectable Hα emission. In these objects the [O ii] emission is presumably either obscured by dust or present with a low signal-to-noise ratio, whilst the (Hγ, Hβ) absorption features are subject to emission-filling. [ABSTRACT FROM AUTHOR]

We reconstruct the underlying density field of the Two-degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 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. We use a variable smoothing technique with two different effective resolutions: 5 and 10 h−1 Mpc at the median redshift of the survey. We identify all major superclusters and voids in the survey. In particular, we find two large superclusters and two large local voids. The full set of colour maps can be viewed on the World Wide Web at . [ABSTRACT FROM AUTHOR]

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 per cent confidence 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 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). [ABSTRACT FROM AUTHOR]

We derive the fraction of blue galaxies in a sample of clusters at 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. [ABSTRACT FROM AUTHOR]

The clustering properties of local, , radio sources are investigated for a sample of 820 objects drawn from the joint use of the Faint Images of the Radio Sky at 20 cm (FIRST) and 2dF Galaxy Redshift surveys. To this aim, we present 271 new spectroscopic counterparts of FIRST radio sources to be added to those already introduced in our previous paper. 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 , while from the projected correlation function Ξ( rT) we estimate the parameters of the real-space correlation function and , where is assumed. Different results are instead obtained if we only consider sources that present signatures of active galactic nucleus (AGN) activity in their spectra. These objects are shown to be very strongly correlated, with and , 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 haloes more massive than , higher than the corresponding figure for radio-quiet quasi-stellar objects. This value can be converted into a minimum black hole mass associated with radio-loud, AGN-fuelled objects of . 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. [ABSTRACT FROM AUTHOR]

We analyse the observed correlation between galaxy environment and Hα emission-line strength, using volume-limited samples and group catalogues of 24 968 galaxies at , drawn from the 2dF Galaxy Redshift Survey ( M bJ< −19.5) and the Sloan Digital Sky Survey . We characterize the environment by: (1) Σ5, the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) ρ1.1 and ρ5.5, three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterized by their Hα equivalent width, W0(Hα). The relative numbers of star-forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W0(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, ρ5.5, which is likely independent of the trend with local density, ρ1.1. We use two differently selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for . 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-time-scale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy–galaxy interactions. [ABSTRACT FROM AUTHOR]

The construction of a catalogue of galaxy groups from the Two-degree Field Galaxy Redshift Survey (2dFGRS) is described. Groups are identified by means of a friends-of-friends 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 World Wide Web. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the two-point correlation function, , from the 2dF Galaxy Redshift Survey (2dFGRS). The large size of the catalogue, which contains ∼220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is , and similarly the effective luminosity, . We estimate the redshift-space correlation function, , from which we measure the redshift-space clustering length, . We also estimate the projected correlation function, , and the real-space correlation function, , which can be fit by a power law , with . For drops below a power law as, for instance, is expected in the popular Λ cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8– gives an estimate of the redshift-space distortion parameter β. The quadrupole moment of on scales 30– provides another estimate of β. We also estimate the distribution function of pairwise peculiar velocities, f( v), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our ξ(σ, π) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of ξ( r) and the two redshift-space distortion effects parametrized by β and velocity dispersion, a. We find and , although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(σ), and find that the shape is consistent with models and simulations. This is the first time that β and f( v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that , and that the present-day matter density of the Universe, , consistent with other 2dFGRS estimates and independent analyses. [ABSTRACT FROM AUTHOR]

Focuses on two-point correlation functions in redshift space for galaxies of different spectral types in the galaxy redshift survey. Estimate of the linear redshift space distortion parameter; Tendency of the relative bias to a constant; Consistency of the result with similar degrees of redshift space distortions.

ABSTRACT We have determined the composite luminosity function (LF) for galaxies in 60 clusters from the 2dF Galaxy Redshift Survey. The LF spans the range -22.5 < M[sub b[sub J]] < -15 , and is well fitted by a Schechter function with M*[sub b[sub J]]=-20.07 ± 0.07 and α=-1.28 ± 0.03 (H[sub 0]= 100 km s[sup -1] Mpc[sup -1], Ω[sub M]= 0.3, Ω[sub Λ]= 0.7) . It differs significantly from the field LF, having a characteristic magnitude that is approximately 0.3 mag brighter and a faint-end slope that is approximately 0.1 steeper. There is no evidence for variations in the LF across a wide range of cluster properties: the LF is similar for clusters with high and low velocity dispersions, for rich and poor clusters, for clusters with different Bautz–Morgan types, and for clusters with and without substructure. The core regions of clusters differ from the outer parts, however, in having an excess of very bright galaxies. We also construct the LFs for early (quiescent), intermediate and late (star-forming) spectral types. We find that, as in the field, the LFs of earlier-type galaxies have brighter characteristic magnitudes and shallower faint-end slopes. However, the LF of early-type galaxies in clusters is both brighter and steeper than its field counterpart, although the LF of late-type galaxies is very similar. The trend of faint-end slope with spectral type is therefore much less pronounced in clusters than in the field, explaining why variations in the mixture of types do not lead to significant differences in the cluster LFs. The differences between the field and cluster LFs for the various spectral types can be qualitatively explained by the suppression of star formation in the dense cluster environment, together with mergers to produce the brightest early-type galaxies. [ABSTRACT FROM AUTHOR]

We constrain fiat 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 Ωm, 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 is shown to follow the simple relation &Omega[sub m] h[sup 3.4] = constant. Adding the 2dF-GRS power spectrum constrains Ω[sub m] h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant of h = 0.665 ± 0.047, the matter density Ω[sub m] = 0.313 ± 0.055, and the physical cold dark matter and baryon densities Ω[sub c] h² = 0.115 ± 0.009, Ω[sub b] h² = 0.022 ± 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set an upper limit to the tensorto-scalar ratio of r < 0.7 at a 95 per cent confidence level. 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 per cent 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/. [ABSTRACT FROM AUTHOR]

We use more than 110 500 galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the b[sub J]-band galaxy luminosity function at redshift z = 0, taking account of evolution, the distribution of magnitude measurement errors and small corrections for incompleteness in the galaxy catalogue. Throughout the interval -16.5 > Mb[sub J] - 5 log[sub 10] h >-22, the luminosity function is accurately described by a Schechter function with M[sup *][sub b][sub J] - 5 log[sub 10] h = -19.66 ± 0.07, α = -1.21 ± 0.03 and Φ[sup *] = (1.61 ± 0.08) × 10[sup -2] h³ Mpc[sup -3], giving an integrated luminosity density of ρ[sub L] = (1.82 ± 0.17) × 10[sup 8] h L[sub ...] Mpc[sup -3] (assuming an Ω[sub 0] = 0.3, Λ[sub 0] = 0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zero-point, from large-scale structure in the galaxy distribution and, importantly, from the uncertainty in the appropriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than, an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the b[sub J] band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on apparent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented. [ABSTRACT FROM AUTHOR]

Abstract We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than M[sub b]=-19 (Ω[sub Λ]= 0.7 , Ω[sub m]= 0.3 , H[sub 0]= 70 km s[sup -1] Mpc[sup -1]) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ* , the star formation rate normalized to L* , as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc[sup -2] (brighter than M[sub b]=-19 ). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present-day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment. [ABSTRACT FROM AUTHOR]

We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with S≥1 mJy . 557 objects (hereafter called the spectroscopic sample) drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS catalogue within the area 9[sup h]48[sup m]&lsim;RA(2000)&lsim;14[sup h]32[sup m] and -2°.77&lsim;Dec.(2000)&lsim;2°.25 , down to a magnitude limit b[sub J]=19.45 . The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra. Absorption-line systems make up 63 per cent of the spectroscopic sample. These may or may not show emission lines due to AGN activity, and correspond to ‘classical’ radio galaxies belonging mainly to the FRI class. They are characterized by relatively high radio-to-optical ratios, red colours, and high radio luminosities (10[sup 21]&lsim;P[sub 1.4 GHz]/W Hz[sup -1] sr[sup -1]&lsim;10[sup 24]) . Actively star-forming galaxies contribute about 32 per cent of the sample. These objects are mainly found at low redshifts (z&lsim;0.1) and show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies (3 per cent) and four Seyfert 1s (1 per cent). Analysis of the local radio luminosity function (LF) shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers P[sub 1.4 GHz]&lsim;10[sup 20.5] W Hz[sup -1] sr[sup -1] . Late-type galaxies, whose relative contribution to the radio LF is found to be lower than was predicted by previous works, present an LF which is comparable with the IRAS galaxy LF. This class of sources therefore plausibly constitutes the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 μm. [ABSTRACT FROM AUTHOR]

We calculate the optical b[sub J] luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope (α) as one moves from passive (α=-0.54) to active (α=-1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude M*-5 log[sub 10](h) (from -19.6 to -19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies [M[sub b[sub J]]-5 log[sub 10](h) fainter than -16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k-corrections, and investigate possible fibre-aperture biases. [ABSTRACT FROM AUTHOR]

We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines (‘late types’) and more quiescent galaxies (‘early types’). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<(σ/h-1 Mpc)<15 , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L* and 4L*. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity. [ABSTRACT FROM AUTHOR]

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 ns and nt. On its own, the 2dFGRS sets tight limits on the parameter combination ω[sub m]h, but relatively weak limits on the fraction of the cosmic matter density in baryons ω[sub b]/ω[sub m]. (Here h is Hubble's constant H[sub 0] in units of 100 km s-[sup -1] Mpc[sup 1]. The cosmic densities in baryons, cold dark matter and vacuum energy are denoted by ω[sub b], ω[sub c] and ωλ, respectively. The total matter density is ω[sub m] = &omega[sub b] + &omega[sub c] and the curvature is fixed by ω[sub k] = 1 - ω[sub m] - ωλ.) The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a 'geometrical degeneracyrsquo; 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 (ω[sub b] = ω[sub b]h ² and ω[sub c] = &omega[sub c]h²). 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 ± 2σ range of 0.65 < ω&λ < 0.85, independently of constraints on ωA derived from Type Ia supernovae. [ABSTRACT FROM AUTHOR]

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250 000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey data base. The 2dFGRS uses the 2dF multifibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2° diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than . The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning around the SGP, and the other in the northern Galactic hemisphere spanning along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 deg[sup 2] and has a median depth of . Adaptive tiling is used to give a highly uniform sampling rate of 93 per cent over the whole survey region. Redshifts are measured from spectra covering at a two-pixel resolution of 9.0 Å and a median S/N of 13 pixel[sup -1]. All redshift identifications are visually checked and assigned a quality parameter Q in the range redshifts are 98.4 per cent reliable and have an rms uncertainty of 85 km s[sup -1]. The overall redshift completeness for redshifts is 91.8 per cent, but this varies with magnitude from 99 per cent for the brightest galaxies to 90 per cent for objects at the survey limit. The 2dFGRS data base is available on the World Wide Web at http://www.mso.anu.edu.au/2dFGRS. [ABSTRACT FROM AUTHOR]

Investigates the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey. Distortion of the clustering pattern induced by peculiar motion; Inclusion of the hierarchical galaxy formation models; Estimation of the correlation function.

Analyzes galaxy clustering in the two-degree-field Galaxy Redshift Survey (2dFGRS), which supports the simplest picture of cosmological structure formation in which the primary mechanism is gravitational instability in a sea of collisionless dark matter. Extrapolation of the fluctuations in the cosmic microwave background (CMB) to predict the peculiar velocities that distort redshift-space clustering; Results favoring a low-density Universe with OMEGA approximately equal to 0.3.