Showing papers by "Carlton M. Baugh published in 2004"
Durham University1, Carnegie Mellon University2, University of New South Wales3, Johns Hopkins University4, Australian National University5, Liverpool John Moores University6, University of St Andrews7, University of Cambridge8, California Institute of Technology9, University of Nottingham10, ETH Zurich11, University of Edinburgh12
TL;DR: In this article, the authors analyzed the observed correlation between galaxy environment and Halpha emission-line strength, using volume-limited samples and group catalogues of 24 968 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).
Abstract: We analyse the observed correlation between galaxy environment and Halpha emission-line strength, using volume-limited samples and group catalogues of 24 968 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 characterize the environment by: (1) Sigma(5), the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) rho(1.1) and rho(5.5), 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 H equivalent width, W-0(Halpha). The relative numbers of star-forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W-0(Halpha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho(5.5), which is likely independent of the trend with local density, rho(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 sigma = 200-1000 km s(-1). Even in the lowest-density environments, no more than similar to70 per cent of galaxies show significant Halpha 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.
560Â citations
Durham University1, ETH Zurich2, University of Edinburgh3, Johns Hopkins University4, Australian National University5, Liverpool John Moores University6, University of New South Wales7, University of Oxford8, Rutherford Appleton Laboratory9, University of Cambridge10, California Institute of Technology11, University of Leeds12, University of Nottingham13, University of California, Berkeley14
TL;DR: The 2DFGRS percolation-inferred galaxy group (2PIGG) catalogue as discussed by the authors is a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS).
Abstract: 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 � 190000 galaxies considered are placed into groups containing at least two members of which � 29000 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 260kms 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.
371Â citations
TL;DR: The 2DFGRS percolation-inferred galaxy group (2PIGG) catalogue as mentioned in this paper is a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS).
Abstract: 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-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% of interlopers. About 55% of the ~190000 galaxies considered are placed into groups containing at least two members of which ~29000 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 260km/s. This 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue represents the largest available homogeneous sample of galaxy groups. It is publicly available on the WWW.
365Â citations
University of Edinburgh1, Durham University2, Queen's University3, Liverpool John Moores University4, University of New South Wales5, Rutherford Appleton Laboratory6, University of Oxford7, Australian National University8, University of Cambridge9, California Institute of Technology10, Johns Hopkins University11, Australia Telescope National Facility12, University College London13, University of Leeds14, University of Nottingham15, ETH Zurich16
TL;DR: In this paper, a decomposition of the 2dF Galaxy Redshift Survey (2dFGRS) galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions is presented.
Abstract: We present the result of a decomposition of the 2dF Galaxy Redshift Survey (2dFGRS) galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions. Galaxies are expected to directly follow the bulk motion of the density field on large scales, so the absolute amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties. By splitting the overdensity field into radial and angular components, we linearly model the observed distortion and obtain the cosmological constraint Omega(m)(0.6)sigma(8)=0.46+/-0.06. The amplitude of the linear redshift-space distortions relative to the galaxy overdensity field is dependent on galaxy properties and, for L-*, galaxies at redshift z=0, we measure beta(L-*, 0)=0.58+/-0.08, and the amplitude of the overdensity fluctuations b(L-*, 0)sigma(8)=0.79+/-0.03, marginalizing over the power spectrum shape parameters. Assuming a fixed power spectrum shape consistent with the full Fourier analysis produces very similar parameter constraints.
229Â citations
Durham University1, ETH Zurich2, University of Edinburgh3, Johns Hopkins University4, Australian National University5, Liverpool John Moores University6, University of New South Wales7, University of Oxford8, Rutherford Appleton Laboratory9, University of Cambridge10, California Institute of Technology11, University College London12, University of Leeds13, University of Nottingham14, University of California, Berkeley15
TL;DR: In this paper, the authors used the 2DFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue of ∼29,000 objects to study the luminous content of galaxy systems of various sizes.
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≲ 1010h−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.
159Â citations
TL;DR: In this paper, a Schechter function is found to be a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, but 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.
Abstract: The 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue of ~29000 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. A Schechter function is found to be a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data. The characteristic luminosity L* is 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. The variation of halo mass-to-light ratio with group size is studied in both these wavebands. A robust trend of increasing M/L with increasing group luminosity is found in the 2PIGG data. From groups with L_bj=10^{10}Lsol to those 100 times more luminous, the typical bj-band M/L increases by a factor of 5, whereas the rf-band M/L grows by a factor of 3.5. These trends agree well with the simulations, which also predict a minimum M/L on a scale corresponding to the Local Group. Our data indicate that if such a minimum exists, then it must occur at L<~10^{10}Lsol, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bj M/Ls of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data yields an estimate of Omega_m=0.26+/-0.03 (statistical).
131Â citations
University of New South Wales1, University of Oxford2, Johns Hopkins University3, Durham University4, Australian National University5, Liverpool John Moores University6, Rutherford Appleton Laboratory7, University of Cambridge8, California Institute of Technology9, Australia Telescope National Facility10, University of Leeds11, University of Nottingham12, Lawrence Berkeley National Laboratory13, ETH Zurich14, University of Edinburgh15
TL;DR: In this article, the authors select a sample of low-redshift E+A galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) and quantify the local environments, clustering properties and luminosity function of these galaxies.
Abstract: We select a sample of low-redshift (z similar to 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 (Hdelta, Hgamma, Hbeta) combined with a lack of [O II] 3727-Angstrom 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 Hdeltagammabeta 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 Hdelta absorption leads to a significant subpopulation of disc systems with detectable Ha 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 (Hgamma, Hbeta) absorption features are subject to emission-filling.
130Â citations
TL;DR: In this article, the authors developed an analytic model to calculate the rate at which galaxy discs are heated by dark matter substructures orbiting in their haloes, taking into account the internal structure, mass function and accretion rate of satellites expected in the ΛCDM cosmology, but it ignores resonant heating of the disc and the dynamical effects of spiral arms and bars.
Abstract: We develop an analytic model to calculate the rate at which galaxy discs are heated by dark matter substructures orbiting in their haloes. The model takes into account the internal structure, mass function and accretion rate of satellites expected in the ΛCDM cosmology, as well as the growth of the disc by accretion and mergers, but it ignores resonant heating of the disc and the dynamical effects of spiral arms and bars. We calibrate this model against N-body simulations and demonstrate that it is able to reproduce the N-body heating rates to within a factor of 3 in the majority of cases. Our model gives the distribution of disc scaleheights for galaxies of different luminosities. For L* spiral galaxies, it predicts a median disc thickness of only 5 per cent of the radial scalelength if substructure is the only source of heating. The median disc thickness increases to nearly 20 per cent of the radial scalelength when heating due to gravitational scattering of stars by molecular clouds is also included. The latter value is close to the thickness estimated observationally for the disc of the Milky Way galaxy. The distribution of disc thickness predicted by the model is also consistent with a recent observational determination for sub-L* galaxies by Bizyaev & Mitronova. Thus, the observed thickness of the stellar discs of spiral galaxies seems to be entirely compatible with the abundance of substructure in dark matter haloes predicted by the standard Λ-dominated cold dark matter model of structure formation. In an Ω0= 1 universe, our best model of galaxy formation produces similar scaleheights, a consequence of the fact that similar amounts of substructure are accreted by haloes during the lifetime of the disc in Ω0= 1 and 0.3, Λ0= 0.7 cold dark matter cosmologies.
121Â citations
Australian National University1, University of Edinburgh2, University of New South Wales3, Durham University4, Johns Hopkins University5, Queen's University6, Liverpool John Moores University7, University of Oxford8, Rutherford Appleton Laboratory9, University of Cambridge10, California Institute of Technology11, University of Nottingham12, Australia Telescope National Facility13, University of Leeds14, Lawrence Berkeley National Laboratory15, ETH Zurich16
TL;DR: In this article, the authors derived the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift and showed that 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 does not depend on cluster properties.
Abstract: 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.
113Â citations
Middle East Technical University1, University of Cambridge2, University College London3, University of Groningen4, University of Edinburgh5, Australian National University6, Johns Hopkins University7, Durham University8, Liverpool John Moores University9, University of New South Wales10, University of Oxford11, Rutherford Appleton Laboratory12, California Institute of Technology13, University of Leeds14, University of Nottingham15, Lawrence Berkeley National Laboratory16, ETH Zurich17
TL;DR: In this article, the authors reconstruct the underlying density field of the Two-degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 0.035
Abstract: We reconstruct the underlying density field of the Two-degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 0.035
95Â citations
Max Planck Society1, Spanish National Research Council2, Durham University3, ETH Zurich4, Australian National University5, Johns Hopkins University6, Queen's University7, Liverpool John Moores University8, University of New South Wales9, University of Oxford10, Rutherford Appleton Laboratory11, University of Cambridge12, California Institute of Technology13, Australia Telescope National Facility14, University College London15, University of Leeds16, University of Nottingham17, University of California, Berkeley18, University of Edinburgh19
TL;DR: In this paper, the authors measured the moments of the galaxy count probability distribution function in the Two-degree Field Galaxy Redshift Survey (2dFGRS) to examine the dependence of the higher-order clustering on galaxy luminosity.
Abstract: We measure moments of the galaxy count probability distribution function in the Two-degree Field Galaxy Redshift Survey (2dFGRS). The survey is divided into volume-limited subsamples in order to examine the dependence of the higher-order clustering on galaxy luminosity. We demonstrate the hierarchical scaling of the averaged p-point galaxy correlation functions, ξ p , up to p = 6. The hierarchical amplitudes, Sp = ξ p /ξ p-1 2, are approximately independent of the cell radius used to smooth the galaxy distribution on small to medium scales. On larger scales we find that the higher-order moments can be strongly affected by the presence of rare, massive superstructures in the galaxy distribution. The skewness S 3 has a weak dependence on luminosity, approximated by a linear dependence on log luminosity. We discuss the implications of our results for simple models of linear and non-linear bias that relate the galaxy distribution to the underlying mass.
Max Planck Society1, Australian National University2, Spanish National Research Council3, Durham University4, ETH Zurich5, Johns Hopkins University6, Queen's University7, Liverpool John Moores University8, University of New South Wales9, Rutherford Appleton Laboratory10, University of Oxford11, University of Cambridge12, California Institute of Technology13, Australia Telescope National Facility14, University College London15, University of Leeds16, University of Nottingham17, University of California, Berkeley18, University of Edinburgh19
TL;DR: In this article, the authors measured the redshift space reduced void probability function (VPF) for 2dFGRS volume limited galaxy samples covering the absolute magnitude range MbJ 5log10 h = 18 to 22.
Abstract: We measure the redshift space reduced void probability function (VPF) for 2dFGRS volume limited galaxy samples covering the absolute magnitude range MbJ 5log10 h = 18 to 22. Theoretically, the VPF connects the distribution of voids to the moments of galaxy clustering of all orders, and can be used to discriminate clustering models in the weakly non-linear regime. The reduced VPF measured from the 2dFGRS is in excellent agreement with the paradigm of hierarchical scaling of the galaxy clustering moments. The accuracy of our measurement is such that we can rule out, at a very high significance, popular models for galaxy clustering, including the lognormal distribution. We demonstrate that the negative binomial model gives a very good approximation to the 2dFGRS data over a wide range of scales,
Durham University1, ETH Zurich2, Max Planck Society3, Johns Hopkins University4, Queen's University5, Australian National University6, Liverpool John Moores University7, University of New South Wales8, Rutherford Appleton Laboratory9, University of Oxford10, University of Cambridge11, California Institute of Technology12, University College London13, University of Leeds14, University of Nottingham15, University of California, Berkeley16, University of Edinburgh17
TL;DR: In this article, the authors measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue and demonstrate that the results are in very good agreement with the theoretical predictions.
Abstract: 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 10 times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the
Durham University1, Max Planck Society2, Spanish National Research Council3, ETH Zurich4, Johns Hopkins University5, Queen's University6, Liverpool John Moores University7, University of New South Wales8, Rutherford Appleton Laboratory9, University of Oxford10, Australian National University11, University of Cambridge12, California Institute of Technology13, Australia Telescope National Facility14, University College London15, University of Leeds16, University of Nottingham17, University of California, Berkeley18, University of Edinburgh19
TL;DR: In this paper, the authors used the Two-Degree Field Galaxy Redshift Survey (2dFGRS) to test the hierarchical scaling hypothesis, namely, that the p-point galaxy correlation functions can be written in terms of the two-point correlation function or variance.
Abstract: We use the Two-Degree Field Galaxy Redshift Survey (2dFGRS) to test the hierarchical scaling hypothesis: namely, that the p-point galaxy correlation functions can be written in terms of the two-point correlation function or variance. This scaling is expected if an initially Gaussian distribution of density fluctuations evolves under the action of gravitational instability. We measure the volume-averaged p-point correlation functions using a counts-in-cells technique applied to a volume-limited sample of 44 931 L-* galaxies. We demonstrate that L-* galaxies display hierarchical clustering up to order p= 6 in redshift space. The variance measured for L-* galaxies is in excellent agreement with the predictions from a Lambda-cold dark matter N-body simulation. This applies to all cell radii considered, 0.3 < (R/h(-1) Mpc) < 30. However, the higher order correlation functions of L-* galaxies have a significantly smaller amplitude than is predicted for the dark matter for R < 10 h(-1) Mpc. This disagreement implies that a non-linear bias exists between the dark matter and L-* galaxies on these scales. We also show that the presence of two rare, massive superclusters in the 2dFGRS has an impact on the higher-order clustering moments measured on large scales.
Max Planck Society1, Australian National University2, Spanish National Research Council3, Durham University4, ETH Zurich5, Johns Hopkins University6, Queen's University7, Liverpool John Moores University8, University of New South Wales9, Rutherford Appleton Laboratory10, University of Oxford11, University of Cambridge12, California Institute of Technology13, Australia Telescope National Facility14, University College London15, University of Leeds16, University of Nottingham17, University of California, Berkeley18, University of Edinburgh19
TL;DR: In this article, the authors measured the redshift space reduced void probability function (VPF) for 2dFGRS volume limited galaxy samples covering the absolute magnitude range M_bJ-5logh=-18 to -22.
Abstract: We measure the redshift space reduced void probability function (VPF) for 2dFGRS volume limited galaxy samples covering the absolute magnitude range M_bJ-5logh=-18 to -22. Theoretically, the VPF connects the distribution of voids to the moments of galaxy clustering of all orders, and can be used to discriminate clustering models in the weakly non-linear regime. The reduced VPF measured from the 2dFGRS is in excellent agreement with the paradigm of hierarchical scaling of the galaxy clustering moments. The accuracy of our measurement is such that we can rule out, at a very high significance, popular models for galaxy clustering, including the lognormal distribution. We demonstrate that the negative binomial model gives a very good approximation to the 2dFGRS data over a wide range of scales, out to at least 20h-1Mpc. Conversely, the reduced VPF for dark matter in a LambdaCDM universe does appear to be lognormal on small scales but deviates significantly beyond \approx 4h-1Mpc. We find little dependence of the 2dFGRS reduced VPF on galaxy luminosity. Our results hold independently in both the north and south Galactic pole survey regions.
TL;DR: In this paper, the authors measured the moments of the galaxy count probability distribution function in the two-degree field galaxy redshift survey (2dFGRS) to examine the dependence of the higher order clustering on galaxy luminosity.
Abstract: We measure moments of the galaxy count probability distribution function in the two-degree field galaxy redshift survey (2dFGRS). The survey is divided into volume limited subsamples in order to examine the dependence of the higher order clustering on galaxy luminosity. We demonstrate the hierarchical scaling of the averaged p-point galaxy correlation functions, xibar_p, up to p=6. The hierarchical amplitudes, S_p = xibar_p/xibar_2^{p-1}, are approximately independent of the cell radius used to smooth the galaxy distribution on small to medium scales. On larger scales we find the higher order moments can be strongly affected by the presence of rare, massive superstructures in the galaxy distribution. The skewness S_3 has a weak dependence on luminosity, approximated by a linear dependence on log luminosity. We discuss the implications of our results for simple models of linear and non-linear bias that relate the galaxy distribution to the underlying mass.
TL;DR: In this paper, the authors used the GALFORM semi-analytical model to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-$\alpha$ photons, the redshift at which the universe reionised and the cosmological density parameter.
Abstract: We present predictions for the abundance of Ly-$\alpha$ emitters in hierarchical structure formation models. We use the {\tt GALFORM} semi-analytical model to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-$\alpha$ photons, the redshift at which the universe reionised and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. We present predictions for the expected counts in a typical observation with the Multi Unit Spectroscopic Explorer instrument proposed for the Very Large Telescope.
TL;DR: In this paper, the authors measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue and demonstrate that the results are in very good agreement with the clusters expected in the LCDM model.
Abstract: We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 29,000 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 LCDM model.
University of Hawaii1, University of Texas at Dallas2, Goddard Space Flight Center3, University of Maryland, Baltimore County4, Australian National University5, Johns Hopkins University6, Durham University7, Queen's University8, Liverpool John Moores University9, University of New South Wales10, University of Oxford11, Rutherford Appleton Laboratory12, University of Cambridge13, California Institute of Technology14, University of Nottingham15, Australia Telescope National Facility16, University of Leeds17, Lawrence Berkeley National Laboratory18, ETH Zurich19, University of Edinburgh20
TL;DR: In this paper, 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.
Abstract: 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).
TL;DR: In this paper, the authors examined the contribution of central and satellite galaxies to the HOD, more specifically to the probability P(N|M) that a halo of virial mass M contains N galaxies of a particular class.
Abstract: The halo occupation distribution (HOD) describes the relation between galaxies and dark matter at the level of individual dark matter halos. The properties of galaxies residing at the centers of halos differ from those of satellite galaxies because of differences in their formation histories. Using a smoothed particle hydrodynamics (SPH) simulation and a semi-analytic (SA) galaxy formation model, we examine the separate contributions of central and satellite galaxies to the HOD, more specifically to the probability P(N|M) that a halo of virial mass M contains N galaxies of a particular class. In agreement with earlier results for dark matter subhalos, we find that the mean occupation function for galaxies above a baryonic mass threshold can be approximated by a step function for central galaxies plus a power law for satellites, and that the distribution of satellite numbers is close to Poisson at fixed halo mass. For galaxy samples defined by different baryonic mass thresholds, there is a nearly linear relation between the minimum halo mass Mmin required to host a central galaxy and the mass M1 at which an average halo hosts one satellite, with M1 ~ 14 Mmin (SPH) or M1 ~ 18 Mmin (SA). The mean occupation number of young galaxies exhibits a local minimum at M ~ 10 Mmin where halos are too massive to host a young central galaxy but not massive enough to host satellites. We show that the conditional galaxy mass function at fixed halo mass cannot be described by a Schechter function because central galaxies produce a "bump" at high masses. We suggest parameterizations for the HOD and the conditional luminosity function that can be used to model observed galaxy clustering. Many of our predictions are in good agreement with recent results inferred from clustering in the Sloan Digital Sky Survey.
TL;DR: The Square Kilometer Array (SKA) as mentioned in this paper was proposed to provide the only means of studying the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the roles of gas accretion and galaxy merging.
TL;DR: The Square Kilometre Array (SKA) as discussed by the authors was proposed to study the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter overdensities and the roles of gas accretion and galaxy merging.
Abstract: The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics - understanding how galaxies form - and astro-particle physics - inferring properties of the dark components. The Square Kilometre Array (SKA) will provide the only means of studying the cosmic evolution of neutral Hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the roles of gas accretion and galaxy merging. `All hemisphere' HI redshift surveys to redshift 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H0 using extragalactic water masers. The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.
TL;DR: In this article, the authors use the GALFORM semi-analytical model to compute the evolution of the neutral hydrogen mass function with redshift and combine it with the spectro-photometric code GRASIL to make predictions for the number counts of radio sources whose radio emission is driven by star formation.
TL;DR: In this paper, the relative bias between early and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) was analyzed using a maximum likelihood technique.
Abstract: We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS). 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. 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 directly fit deterministic models for the joint density distribution function, f(delta_E,delta_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. (abridged)
University of Edinburgh1, Durham University2, Queen's University3, Liverpool John Moores University4, University of New South Wales5, University of Oxford6, Rutherford Appleton Laboratory7, Australian National University8, University of Cambridge9, California Institute of Technology10, Johns Hopkins University11, Australia Telescope National Facility12, University College London13, University of Leeds14, University of Nottingham15, ETH Zurich16
TL;DR: In this paper, a decomposition of the 2dFGRS galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions is presented. And the amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties.
Abstract: We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions. Galaxies are expected to directly follow the bulk motion of the density field on large scales, so the absolute amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties. By splitting the overdensity field into radial and angular components, we linearly model the observed distortion and obtain the cosmological constraint Omega_m^{0.6} sigma_8=0.46+/-0.06. The amplitude of the linear redshift-space distortions relative to the galaxy overdensity field is dependent on galaxy properties and, for L_* galaxies at redshift z=0, we measure beta(L_*,0)=0.58+/-0.08, and the amplitude of the overdensity fluctuations b(L_*,0) sigma_8=0.79+/-0.03, marginalising over the power spectrum shape parameters. Assuming a fixed power spectrum shape consistent with the full Fourier analysis produces very similar parameter constraints.
Max Planck Society1, New York University2, ETH Zurich3, University of Edinburgh4, Johns Hopkins University5, Durham University6, Queen's University7, Liverpool John Moores University8, University of New South Wales9, University of Oxford10, Rutherford Appleton Laboratory11, University of Bristol12, Australian National University13, University of Cambridge14, California Institute of Technology15, Australia Telescope National Facility16, University College London17, University of Leeds18, University of Nottingham19, University of California, Berkeley20
TL;DR: In this paper, the authors measured the dependence of the bJ-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h-1Mpc, and on spectral type, determined from principal component analysis.
Abstract: We use the 2dF Galaxy Redshift Survey to measure the dependence of the bJ-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h-1Mpc, and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M_bJ-5log10h <-18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M_bJ-5log10h < -21. Differences in the mid to faint-end population between environments are significant: at M_bJ-5log10h=-18 early and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion which differs strikingly for early and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation.
TL;DR: In this article, the authors performed a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, eta, as early or late type galaxies.
Abstract: It is well known that the clustering of galaxies depends on galaxy type.Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, eta, as early or late type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the nonlinearity and stochasticity of the relative bias, with cubical cells of side 10Mpc \leq L \leq 45Mpc (h=0.7). Exact linear bias is ruled out with high significance on all scales. Power law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero `stochasticity' - i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (r_LN) of 0.958 for cells of length L=10Mpc, increasing to 0.970 by L=45Mpc. This corresponds to a stochasticity sigma_b/bhat of 0.44\pm0.02 and 0.27\pm0.05 respectively. For smaller cells, the Poisson sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semianalytic galaxy formation models: these match the data well in terms of overall level of stochasticity, variation with scale, and fraction of empty cells.
TL;DR: In this paper, the abundance of sub-mm galaxies (SMGs) and Lyman-break galaxies (LBGs) in the Lambda$CDM cosmology is predicted, based on the self-consistent calculation of the absorption and emission of radiation by dust.
Abstract: We present predictions for the abundance of sub-mm galaxies (SMGs) and Lyman-break galaxies (LBGs) in the $\Lambda$CDM cosmology. A key feature of our model is the self-consistent calculation of the absorption and emission of radiation by dust. The new model successfully matches the LBG luminosity function, as well reproducing the properties of the local galaxy population in the optical and IR. The model can also explain the observed galaxy number counts at $850\mum$, but only if we assume a top-heavy IMF for the stars formed in bursts. The predicted redshift distribution of SMGs depends relatively little on their flux over the range 1-$10\mjy$, with a median value of $z\approx 2.0$ at a flux of $5\mjy$, in very good agreement with the recent measurement by Chapman et al The counts of SMGs are predicted to be dominated by ongoing starbursts. However, in the model these bursts are responsible for making only a few per cent of the stellar mass locked up in massive ellipticals at the present day.
Australian National University1, University of Edinburgh2, University of New South Wales3, Durham University4, Johns Hopkins University5, Queen's University6, Liverpool John Moores University7, Rutherford Appleton Laboratory8, University of Oxford9, University of Cambridge10, California Institute of Technology11, University of Nottingham12, Australia Telescope National Facility13, University of Leeds14, Lawrence Berkeley National Laboratory15, ETH Zurich16
TL;DR: In this paper, the authors derived the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift and showed that 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 does not depend on cluster properties.
Abstract: 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.
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TL;DR: In this article, the 2dFGRS is used in conjunction with the 2MASSXSC to study the near-IR light and stellar mass content of the local Universe, and the mean luminosity densities of the Universe are found to be rho_J=(3.57+/-0.11)*10^8 h Lsol/Mpc^3 (statistical uncertainty).
Abstract: The 2dFGRS is used in conjunction with the 2MASSXSC to study the near-IR light and stellar mass content of the local Universe. Mock galaxy catalogues, constructed from cosmological N-body simulations and semi-analytical galaxy formation models, are used to gauge the accuracy with which quantities can be recovered. The mean luminosity densities of the Universe are found to be rho_J=(3.57+/-0.11)*10^8 h Lsol/Mpc^3 and rho_KS=(7.04+/-0.23)*10^8 h Lsol/Mpc^3 (statistical uncertainty). Using the 2PIGG catalogue, the group dynamical mass-to-light ratio in the K_S band is found to increase by a factor of ~3 when going from groups with total bJ-band luminosities of 3*10^10 h^-2 Lsol to rich clusters, which have typical values of Upsilon_K~80 h Upsilon_sol. Taking into account the bias introduced by uncertainties in estimating galaxy stellar masses from luminosities, a value of Omega_* h=(0.99+/-0.03)*10^-3 is measured, assuming that a Kennicutt stellar IMF is applicable to all galaxies. The 2PIGGs are then used to study the distribution of the stellar content of the local Universe. The three main conclusions are: (1) a slowly rising stellar M/L_KS is found with the clusters having the largest value of ~0.6 Upsilon_sol, (2) in contrast, the fraction of mass in stars decreases with increasing group size, reaching ~5*10^-3 h for the rich clusters, and (3) in answer to the question posed in the title, most stellar mass is contained in Local Group-sized objects (M~2*10^12 h^-1 Msol) with only ~2% in clusters with M>5*10^14 h^-1 Msol.