Luminosity- and redshift-dependent quasar clustering

We present detailed clustering measurements for a flux-limited sample of ∼14 000 quasars extracted from the 2dF QSO Redshift Survey in the redshift range 0.8 1.3. On the other hand, a number of tests based on information theory and Bayesian statistics show only marginal evidence for luminosity-dependent clustering. Anyway, the quality of the data is not good enough to accurately quantify how quasar biasing depends on luminosity. We critically discuss the limitations of our data set and show that a much larger sample is needed to rule out current models for luminosity segregation. Studying the evolution of the clustering amplitude with redshift, we detect an increase of the quasar correlation length with lookback time at the 99.3 per cent confidence level. Adopting the concordance cosmological model, we discuss the evolution of quasar biasing with cosmic epoch and show that quasars are typically hosted by dark matter haloes with mass ∼1013 M

Analysis of the two degree field galaxy redshift survey

In this Thesis we analyse in detail the Anglo-Australian 2 degree Field Galaxy Redshift Survey (2dFGRS). The goal of this survey is to measure all galaxy redshifts for the 250 000 galaxies brighter than b(_J) = 19.45 spread over ~ 2000 square degrees. At present, the 2dFGRS has obtained redshifts for ~ 190 000 galaxies. It is currently the biggest galaxy redshift survey in existence and represents an order of magnitude increase in size over any previous survey. The study of the large-scale structure of the Universe is undergoing a revolution due to important technological advances in observational astronomy that make surveys like the 2dFGRS possible. This new era in mapping the Universe demands the development of new theoretical analysis tools, both to exploit the large amounts of data, and to take advantage of, for the first time in cosmology, the extraordinary opportunity to push random errors below the level of the systematic errors. By a detailed analysis of the survey construction and observing strategy, we implement a set of maps to estimate, as precisely as possible, the selection function of the 2dFGRS. These maps, which characterize the survey completeness, enable us to estimate accurately fundamental properties of a homogeneous galaxy sample: the galaxy luminosity function and real space galaxy clustering. By combining the 2dFGRS with the near infra-red 2MASS survey, we estimate the K(_s)-band galaxy luminosity function, from which we infer the stellar mass function of galaxies. This yields a total mass fraction in stars between 0.1% and 0.3% of the critical cosmic density. Exploiting the size of the survey, we undertake the first precise measurement of the dependence of galaxy clustering on luminosity and spectral type. Star-forming galaxies as well as more quiescent galaxies show a clear increase in clustering strength with luminosity at a similar rate. This is the first time that we are able to examine in detail the properties of galaxies that drive their spatial distribution

Cosmic evolution of quasar clustering: implications for the host haloes

We present detailed clustering measurements from the 2dF Quasi-Stellar Object Redshift Survey (2QZ) in the redshift range 0.8 1012 M⊙ and that the characteristic mass of their host haloes is of the order of 1013 M⊙. The observed clustering is consistent with assuming that the locally observed correlation between black hole mass and host galaxy circular velocity is still valid at z > 1. From the fraction of haloes which contain active quasars, we infer that the characteristic quasar lifetime is tQ∼ a few × 107 yr at z∼ 1 and approaches 108 yr at higher redshift

Massive dark matter haloes around bright isolated galaxies in the 2dFGRS

We identify a large sample of isolated bright galaxies and their fainter satellites in the 2dF Galaxy Redshift Survey (2dFGRS). We analyse the dynamics of ensembles of these galaxies selected according to luminosity and morphological type by stacking the positions of their satellites and estimating the velocity dispersion of the combined set. We test our methodology using realistic mock catalogues constructed from cosmological simulations. The method returns an unbiased estimate of the velocity dispersion provided that the isolation criterion is strict enough to avoid contamination and that the scatter in halo mass at fixed primary luminosity is small. Using a maximum likelihood estimator that accounts for interlopers, we determine the satellite velocity dispersion within a projected radius of 175 h−1kpc. The dispersion increases with the luminosity of the primary and is larger for elliptical galaxies than for spiral galaxies of similar bJ luminosity. Calibrating the mass-velocity dispersion relation using our mock catalogues, we find a dynamical mass within 175 h−1kpc of for elliptical galaxies and for spiral galaxies. Finally, we compare our results with recent studies and investigate their limitations using our mock catalogue

The real-space clustering of luminous red galaxies around z < 0.6 quasars in the Sloan Digital Sky Survey

We measure the clustering of a sample of photometrically selected luminous red galaxies (LRGs) around a low-redshift (0.2 25 per cen

The anisotropic distribution of satellite galaxies

We identify satellites of isolated galaxies in the Sloan Digital Sky Survey and examine their angular distribution. Using mock catalogues generated from cosmological N-body simulations, we demonstrate that the selection criteria used to select isolated galaxies and their satellites in large galaxy redshift surveys must be very strict in order to correctly identify systems in which the primary galaxy dominates its environment. We demonstrate that the criteria used in many previous studies instead select predominantly group members. We refine a set of selection criteria for which the group contamination is estimated to be less than 7 per cent and present a catalogue of the resulting sample. The angular distribution of satellites about their host is biased towards the major axes for spheroidal galaxies and probably also for red disc galaxies (the ‘intermediate' class of Bailin & Harris), but is isotropic for blue disc galaxies, i.e. it is the colour of the host that determines the distribution of its satellites rather than its morphology. The similar anisotropy measured in this study to studies that were dominated by groups implies that group-specific processes are not responsible for the angular distribution. Satellites that are most likely to have been recently accreted, late-type galaxies at large projected radii, show a tendency to lie along the same axis as the surrounding large-scale structure. The orientations of isolated early- and intermediate-type galaxies also align with the surrounding large-scale structures. We discuss the origin of the anisotropic satellite distribution and consider the implications of our results, critically assessing the respective roles played by the orientation of the visible galaxy within its dark matter halo, anisotropic accretion of satellites from the larger scale environment, and the biased nature of satellites as tracers of the underlying dark matter subhalo populatio

A new marked correlation function scheme for testing gravity

We introduce a new scheme based on the marked correlation function to probe gravity using the large-scale structure of the Universe. We illustrate our approach by applying it to simulations of the metric-variation $f(R)$ modified gravity theory and general relativity (GR). The modifications to the equations in $f(R)$ gravity lead to changes in the environment of large-scale structures that could, in principle, be used to distinguish this model from GR. Applying the Monte Carlo Markov Chain algorithm, we use the observed number density and two-point clustering to fix the halo occupation distribution (HOD) model parameters and build mock galaxy catalogues from both simulations. To generate a mark for galaxies when computing the marked correlation function we estimate the local density using a Voronoi tessellation. Our approach allows us to isolate the contribution to the uncertainty in the predicted marked correlation function that arises from the range of viable HOD model parameters, in addition to the sample variance error for a single set of HOD parameters. This is critical for assessing the discriminatory power of the method. In a companion paper we apply our new scheme to a current large-scale structure survey.Comment: 11 pages, 7 figure

A new test of gravity – II. Application of marked correlation functions to luminous red galaxy samples

We apply the marked correlation function test proposed by Armijo et al. (Paper I) to samples of luminous red galaxies (LRGs) from the final data release of the Sloan Digital Sky Survey (SDSS) III. The test assigns a density-dependent mark to galaxies in the estimation of the projected marked correlation function. Two gravity models are compared: general relativity (GR) and gravity. We build mock catalogues which, by construction, reproduce the measured galaxy number density and two-point correlation function of the LRG samples, using the halo occupation distribution model (HOD). A range of HOD models give acceptable fits to the observational constraints, and this uncertainty is fed through to the error in the predicted marked correlation functions. The uncertainty from the HOD modelling is comparable to the sample variance for the SDSS-III LRG samples. Our analysis shows that current galaxy catalogues are too small for the test to distinguish a popular model from GR. However, upcoming surveys with a better measured galaxy number density and smaller errors on the two-point correlation function, or a better understanding of galaxy formation, may allow our method to distinguish between viable gravity models