Antonaldo Diaferio

• University of Turin

We show that varsigma , the radial location of the minimum in the differential radial mass profile $M^ of a galaxy cluster, can probe the theory of gravity. We derived $M^ of the dark matter halos of galaxy clusters from N-body cosmological simulations that implement two different theories of gravity: standard gravity in the Lambda CDM model, and $...

We used simulated cluster member galaxies from the TNG300-1 run of the IllustrisTNG simulations to develop a technique for measuring the galaxy cluster mass accretion rate (MAR) that can be applied directly to observations. We analyzed 1318 IllustrisTNG clusters of galaxies with M 200c > 10 ¹⁴ M ⊙ and 0.01 ≤ z ≤ 1.04. The MAR we derived is the rati...

The TNG300-1 run of the IllustrisTNG simulations includes 1697 clusters of galaxies with M 200c > 10 ¹⁴ M ⊙ covering the redshift range 0.01 − 1.04. We built mock spectroscopic redshift catalogs of simulated galaxies within these clusters and applied the caustic technique to estimate the cumulative cluster mass profiles. We computed the total true...

Context. Clusters of galaxies are powerful probes with which to study cosmology and astrophysics. However, for many applications, an accurate measurement of a cluster’s mass is essential. A systematic underestimate of hydrostatic masses from X-ray observations (the so-called hydrostatic bias) may be responsible for tension between the results of di...

We show how $\varsigma$, the radial location of the minimum of the differential radial mass profile $M^\prime(r)$ of a galaxy cluster, can probe the theory of gravity. We derive $M^\prime(r)$ of the dark matter halos of galaxy clusters from N-body cosmological simulations that implement two different theories of gravity: standard gravity in the $\L...

We estimate the mass accretion rate (MAR) of 321 clusters of galaxies in the HectoMAP Cluster Survey. The clusters span the redshift range 0.17–0.42 and the M 200 mass range ≈ (0.5–3.5) × 10 ¹⁴ M ⊙ . The MAR estimate is based on the caustic technique along with a spherical infall model. Our analysis extends the measurement of MARs for 129 clusters...

The cold dark-matter model successfully explains both the emergence and evolution of cosmic structures on large scales and, when we include a cosmological constant, the properties of the homogeneous and isotropic Universe. However, the cold dark-matter model faces persistent challenges on the scales of galaxies. Indeed, N-body simulations predict s...

We prove that Conformal Gravity (CG) is unable to describe galactic rotation curves without the aid of dark matter as suggested in the literature: if we interpret CG as a gauge natural theory, we can derive conservation laws and their associated superpotentials without ambiguities. We consider the light deflection of a point-like lens in CG and imp...

We show how Conformal Gravity (CG) has to satisfy a fine-tuning condition to describe the rotation curves of disk galaxies without the aid of dark matter. Interpreting CG as a gauge natural theory yields conservation laws and their associated superpotentials without ambiguities. We consider the light deflection of a point-like lens and impose that...

We discuss the phenomenology of gravitational lensing in the purely metric f(χ) gravity, an f(R) gravity where the action of the gravitational field depends on the source mass. We focus on the strong lensing regime in galaxy-galaxy lens systems and in clusters of galaxies. By adopting point-like lenses and using an approximate metric solution accur...

We discuss the phenomenology of gravitational lensing in the purely metric $f\left(\chi\right)$ gravity, an $f(R)$ gravity where the action of the gravitational field depends on the source mass. We focus on the strong lensing regime in galaxy-galaxy lens systems and in clusters of galaxies. Using an approximate metric solution accurate to second or...

With the Westerbork Synthesis Radio Telescope, we performed HI observations of a sample of known X-ray emitting Gigahertz-peaked-spectrum galaxies with compact-symmetric-object morphology (GPS/CSOs) that lacked an HI absorption detection. We combined radio and X-ray data of the full sample of X-ray emitting GPS/CSOs and found a significant, positiv...

This article explores the agreement between the predictions of modified Newtonian dynamics (MOND) and the rotation curves and stellar velocity dispersion profiles measured by the DiskMass Survey (DMS). A bulge–disk decomposition was made for each of the thirty published galaxies, and a MOND Poisson solver was used to simultaneously compute, from th...

We use our Modified Newtonian Dynamics (MOND) cosmological particle-mesh N-body code to investigate the feasibility of structure formation in a framework involving MOND and light sterile neutrinos in the mass range 11 - 300 eV: always assuming that \Omega_{\nu_s}=0.225 for H_o=72 \kms Mpc^{-1}. We run a suite of simulations with variants on the exp...

We present a spectrophotometric analysis of the galaxy pop. in the area of the merging cluster Abell 3921 at redshift 0.093. We investigate the impact of the complex cluster environment on galaxy properties such as morphology or star formation rate. We combine multi-object spectroscopy from the 2dF spectrograph with optical imaging taken with the E...

The bulge dominated galaxy NGC 7814 provides one of the strongest dynamical tests possible for Modified Newtonian Dynamics (MOND). Spitzer 3.6 micron photometry fixes the bulge parameterisation and strongly constrains the properties of the sub-dominant stellar disk. Furthermore, the distance is known to better than 5 percent, virtually eliminating...

Cluster mass profiles are tests of models of structure formation. Only two current observational methods of determining the mass profile, gravitational lensing, and the caustic technique are independent of the assumption of dynamical equilibrium. Both techniques enable the determination of the extended mass profile at radii beyond the virial radius...

The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M 200 ≥ 1014h –1M ☉ extracted from a cosmological N-body simulation of a ΛCDM universe to test the ability of the caustic technique to identify t...

The infall regions of galaxy clusters represent the largest gravitationally bound structures in a $\Lambda$CDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these haloes. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cl...

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster is not "overconcentrated" as found previously, implying a formation time in agreement with ΛCDM expectations. These results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging obtained as part...

General Relativity is able to describe the dynamics of galaxies and larger cosmic structures only if most of the matter in the Universe is dark, namely it does not emit any electromagnetic radiation. Intriguingly, on the scale of galaxies, there is strong observational evidence that the presence of dark matter appears to be necessary only when the...

Weak gravitational lensing by galaxy clusters on faint higher redshift galaxies has been traditionally used to study the cluster mass distribution and as a tool to identify clusters as peaks in the shear maps. However, it becomes soon clear that peak statistics can also be used as a way to constrain the underlying cosmological model due to its depe...

We use Wide-field Infrared Survey Explorer (WISE) data covering the entire region (~130 deg^2) of the A2199 supercluster at z=0.03 to study the mid-infrared (MIR) properties of supercluster galaxies. We identify a `MIR star-forming sequence' in the WISE [3.4]-[12] color-12 \mu m luminosity diagram, consisting of late-type, star-forming galaxies. At...

The observed accelerated cosmic expansion can be a signature of fourth\,-\,order gravity theories, where the acceleration of the Universe is a consequence of departures from Einstein General Relativity, rather than the sign of the existence of a fluid with negative pressure. In the fourth\,-\,order gravity theories, the gravity Lagrangian is descri...

We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the first time and determine this cluster is not "over-concentrated" as found previously, implying a formation time in agreement with {\Lambda}CDM expectations. These results are based on strong lensing analyses of new 16-band HST imaging obtained as part of the Cluster Lensi...

Redshift surveys are a powerful tool of modern cosmology. We discuss two aspects of their power to map the distribution of mass and light in the universe: (1) measuring the mass distribution extending into the infall regions of rich clusters and (2) applying deep redshift surveys to the selection of clusters of galaxies and to the identification of...

We present a new particle mesh cosmological N-body code for accurately solving the modified Poisson equation of the quasi-linear formulation of modified Newtonian dynamics (MOND). We generate initial conditions for the Angus cosmological model, which is identical to Λ cold dark matter (ΛCDM) except that the CDM is switched for a single species of t...

The highly organised distribution of satellite galaxies surrounding the Milky Way is a serious challenge to the concordance cosmological model. Perhaps the only remaining solution, in this framework, is that the dwarf satellite galaxies fall into the Milky Way's potential along one or two filaments, which may or may not plausibly reproduce the obse...

Smithsonian Hectospec Lensing Survey (SHELS) is a dense redshift survey covering a 4 deg2 region to a limiting R = 20.6. In the construction of the galaxy catalog and in the acquisition of spectroscopic targets, we paid careful attention to the survey completeness for lower surface brightness dwarf galaxies. Thus, although the survey covers a small...

We show that extreme value statistics are useful for studying the largest structures in the Universe by using them to assess the significance of two of the most dramatic structures in the local Universe – the Shapley supercluster and the Sloan Great Wall. If we assume that the Shapley concentration (volume ≈1.2 × 105 h−3 Mpc3) evolved from an overd...

Flexion is the weak lensing effect responsible for the weakly skewed and arc-like appearance of lensed galaxies. The flexion signal-to-noise ratio can be an order of magnitude larger than that of shear. For the first time, we show how this makes flexion an invaluable tool for discriminating among alternative cosmological models. We analyse a scalar...

We present the cosmic shear signal predicted by two viable cosmological models in the framework of modified-action f(R) theories. We use f(R) models where the current accelerated expansion of the Universe is a direct consequence of the modified gravitational Lagrangian rather than Dark Energy (DE), either in the form of vacuum energy/cosmological c...

LambdaCDM, for the currently preferred cosmological density Omega_0 and cosmological constant Omega_Lambda, predicts that the Universe expansion decelerates from early times to redshift z~0.9 and accelerates at later times. On the contrary, the cosmological model based on conformal gravity predicts that the cosmic expansion has always been accelera...

Modified Newtonian dynamics (MOND) has been shown to be able to fit spiral galaxy rotation curves as well as giving a theoretical foundation for empirically determined scaling relations, such as the Tully–Fisher law, without the need for a dark matter halo. As a complementary analysis, one should investigate whether MOND can also reproduce the dyna...

A phenomenological extension of the well-known brane-world cosmology of Dvali, Gabadadze and Porrati (eDGP) has recently been proposed. In this model, a cosmological-constant-like term is explicitly present as a non-vanishing tension sigma on the brane, and an extra parameter alpha tunes the cross-over scale r_c, the scale at which higher dimension...

The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic t...

In this article, we review model selection predictions for modified gravity scenarios as an explanation for the observed acceleration of the expansion history of the Universe. We present analytical procedures for calculating expected Bayesian evidence values in two cases: (i) that modified gravity is a simple parametrized extension of general relat...

In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-peaked-spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium...

We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel'dovich Effect (SZE) signals. We study 15 clusters from the Hectospec Cluster Survey (HeCS) with MMT/Hectospec spectroscopy and published SZE signals. We measure virial masses of these clusters from an average of 90 member redshifts inside the radius r 100. Th...

We present a new multiphase subresolution model for star formation and feedback in smoothed particle hydrodynamics (SPH) numerical simulations of galaxy formation. Our model, called MUPPI (MUlti-Phase Particle Integrator), describes each gas particle as a multiphase system, with cold and hot gas phases, coexisting in pressure equilibrium and a stel...

We present parameter estimation forecasts for future 3D cosmic shear surveys for a class of Unified Dark Matter (UDM) models, where a single scalar field mimics both Dark Matter (DM) and Dark Energy (DE). These models have the advantage that they can describe the dynamics of the Universe with a single matter component providing an explanation for s...

We present a new multi-phase sub-resolution model for star formation and feedback in SPH numerical simulations of galaxy formation. Our model, called MUPPI (MUlti-Phase Particle Integrator), describes each gas particle as a multi-phase system, with cold and hot gas phases, coexisting in pressure equilibrium, and a stellar component. Cooling of the...

We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel'dovich Effect (SZE) signals. We study 15 clusters from the Hectospec Cluster Survey (HeCS) with MMT/Hectospec spectroscopy and published SZE signals. We measure virial masses of these clusters from an average of 90 member redshifts inside the radius $r_{100}$...

Weak gravitational lensing is a powerful tool for studying both the geometry and the dynamics of the Universe. Its power spectrum contains information on the sources emitting photons and on the large-scale structures that these photons cross. We calculate the weak lensing cosmic convergence and shear power spectra, in linear theory and Limber's app...

We present a spectroscopic sample of 910 distant halo stars from the Hypervelocity Star survey from which we derive the velocity dispersion profile of the Milky Way halo. The sample is a mix of 74% evolved horizontal branch stars and 26% blue stragglers. We estimate distances to the stars using observed colors, metallicities, and stellar evolution...

Fourth - order gravity theories have received much interest in recent years thanks to their ability to provide an accelerated cosmic expansion in a matter only universe. In these theories, the Lagrangian density of the gravitational field has the form R + f(R), and the explicit choice of the arbitrary function f(R) must meet the local tests of grav...

Using the caustic method, we identify the member stars of five dwarf spheroidal (dSph) galaxies of the Milky Way, the smallest dark matter (DM) dominated systems in the Universe. After our interloper rejection, we compute line-of-sight velocity dispersion profiles that are substantially smoother than previous results. Moreover, two dSphs have line-...

(Abridged) Modified Newtonian Dynamics (MOND) can fit a broad range of galaxy kinematic data, but struggles with clusters of galaxies. MONDian clusters need dark matter, and here we test the 11 eV sterile neutrino - used to fit the first three acoustic peaks of the cosmic microwave background - by investigating their equilibrium distributions in 30...

We re-investigate the old problem of the survival of the five globular clusters orbiting the Fornax dwarf galaxy in both standard and modified Newtonian dynamics. For the first time in the history of the topic, we use accurate mass models for the Fornax dwarf, obtained through Jeans modelling of the recently published line of sight velocity dispers...

Traditional estimators of the mass of galaxy clusters assume that the cluster components (galaxies, intracluster medium, and dark matter) are in dynamical equilibrium. Two additional estimators, that do not require this assumption, were proposed in the 1990s: gravitational lensing and the caustic technique. With these methods, we can measure the cl...

The study of the broad-band emission of GHz-Peaked-Spectrum (GPS) radio galaxies is a powerful tool to investigate the physical processes taking place in the central, kpc-sized region of their active hosts, where the jets propagate and the lobes expand, interacting with the surrounding interstellar medium (ISM). We recently developed a new dynamica...

We use the Fifth Data Release of the Sloan Digital Sky Survey to study X-ray-selected galaxy groups and compare their properties to clusters. We search for infall patterns around the groups and use these to measure group mass profiles to large radii. In previous work, we analyzed infall patterns for an X-ray-selected sample of 72 clusters from the...

We run adiabatic N-body/hydrodynamical simulations of isolated self-gravitating gas clouds to test whether conformal gravity, an alternative theory to General Relativity, is able to explain the properties of X-ray galaxy clusters without resorting to dark matter. We show that the gas clouds rapidly reach equilibrium with a density profile which is...

We use scalar-field Lagrangians with a non-canonical kinetic term to obtain unified dark matter models where both the dark matter and the dark energy, the latter mimicking a cosmological constant, are described by the scalar field itself. In this framework, we propose a technique to reconstruct models where the effective speed of sound is small eno...

Under the assumption that General Relativity (GR) correctly describes the phenomenology of our Universe, astronomical observations provide compelling evidence that (1) the dynamics of cosmic structure is dominated by dark matter (DM), an exotic matter mostly made of hypothetical elementary particles, and (2) the expansion of the Universe is current...

The recently revised cosmological constraints from the Five-Year WMAP data ameliorate previous tension between cosmological constraints from the microwave background and from cluster abundances. We demonstrate that the revised estimates of cosmological parameters are in excellent agreement with the mass function of X-ray clusters in the Sloan Digit...

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and t...

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and t...

Clusters of galaxies are self-gravitating systems of mass ∼10¹⁴–10¹⁵h⁻¹ M⊙ and size ∼1–3h⁻¹ Mpc. Their mass budget consists of dark matter (∼80%, on average), hot diffuse intracluster plasma (≲20%) and a small fraction of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties, like mass, g...

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds,...

Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat tra...

We discuss H-band (1.65 μm) near-infrared photometry of the central 9 h-2 Mpc2 of Abell 1644 (A1644) to a limiting MH ~ M*H + 3 (throughout this paper H0 = 100 h km s-1 Mpc-1). There are 861 galaxies in the photometric survey region. We also measured radial velocities of 155 galaxies; 141 of these are cluster members within 2.44 h-1 Mpc of the clus...

We compare the properties of galaxy groups extracted from the Updated Zwicky Catalogue (UZC) with those of groups extracted from N-body simulations of the local Universe, in a Λ cold dark matter (CDM) and a τCDM cosmology. In the simulations, the initial conditions of the dark matter density field are set to reproduce the present time distribution...

We present a new determination of the cluster mass function and velocity dispersion function in a volume $\sim10^7 h^3$Mpc$^{-3}$ using the Fourth Data Release of the Sloan Digital Sky Survey (SDSS). We use the caustic technique to remove foreground and background galaxies. The cluster virial mass function agrees well with recent estimates from bot...

We use the Fourth Data Release of the Sloan Digital Sky Survey to test the ubiquity of infall patterns around galaxy clusters and measure cluster mass profiles to large radii. We match X-ray cluster catalogs with SDSS, search for infall patterns, and compute mass profiles for a complete sample of X-ray selected clusters. Very clean infall patterns...

Free electrons within the hot diffuse plasma (ICM) of clusters of galaxies scatter the photons of the Cosmic Microwave Background (CMB), an effect predicted by Zeldovich and Sunyaev (SZ) in 1969. Clusters thus appears as cold (hot) spots in the low (high) radio frequency observations of the CMB. The magnitude of the SZ effect is independent of the...

We discuss an extended set of Tree+SPH simulations of galaxy clusters, with the goal of investigating the interplay between numerical resolution effects and star-formation/feedback processes. The simulated clusters span the mass range (0.1-2.3) 10^{15}Msun/h, with mass resolution varying by several decades. At the highest achieved resolution, we re...

The angular-diameter distance D_A of a galaxy cluster can be measuread by combining its X-ray emission with the cosmic microwave background fluctution due to the Sunyaev-Zeldovich effect. The application of this distance indicator usually assumes that the cluster is spherically symmetric, the gas is distributed according to the isothermal beta-mode...

We investigate the environmental dependence of star formation in cluster virial regions and infall regions as part of the Cluster and Infall Region Nearby Survey (CAIRNS), a large spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. We use complete, homogeneous spectroscopic surveys of Ks-limited samples in...

There are only two methods for estimating the mass distribution in the outer regions of galaxy clusters, where virial equilibrium does not hold: weak gravitational lensing and identification of caustics in redshift space. For the first time, we apply both methods to three clusters: A2390, MS1358 and Cl 0024. The two measures are in remarkably good...

We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular Λ cold dark matter cosmogony. We identify voids by requiring them to be regions of space with a mean overdensity of −0.8 or less – roughly the equivalent of using a spherical overdensity group finder for haloes. Each of the simulat...

The detection of excess of soft X-ray or Extreme Ultraviolet (EUV) radiation, above the thermal contribution from the hot intracluster medium (ICM), has been a controversial subject ever since the initial discovery of this phenomenon. We use a large--scale hydrodynamical simulation of a concordance $\Lambda$CDM model, to investigate the possible th...

In this paper we present the analysis of Beppo-SAX observations of the cluster pairs A2061-A2067 and A2122-A2124, located in the Corona Borealis supercluster, which have been selected as candidate merging clusters. The aim of this work is to study the physics of the intracluster medium and to look for the possible presence of merging signatures. We...

We study the properties of the diffuse light in galaxy clusters forming in a large hydrodynamical cosmological simulation of the Lambda-CDM cosmology. The simulation includes a model for radiative cooling, star formation in dense cold gas, and feedback by SN-II explosions. We select clusters having mass M>10^(14) h^(-1) Msun and study the spatial d...

We present results on the X-ray properties of clusters and groups of galaxies, extracted from a large hydrodynamical simulation. We used the GADGET code to simulate a LambdaCDM model within a box of 192 Mpc/h on a side, with 480^3 dark matter particles and as many gas particles. The simulation includes radiative cooling, star formation and supernov...

We use a simple analytic model to compute the angular correlation function of clusters identified in upcoming thermal Sunyaev—Zel'dovich (SZ) effect surveys. We then compute the expected fraction of close pairs of clusters on the sky that are also close along the line of sight. We show how the expected number of cluster pairs as a function of redsh...

N-body simulations of the formation of the large-scale structure in the Universe have been used to both design and test the halo model, an analytic model which describes the spatial and velocity distribution of galaxies and dark matter halos. Here, we use the halo model to (1) describe the correlation function of galaxies, selected from simulated c...

We combine dissipationless N-body simulations and semi-analytic models of galaxy formation to study the spatial and kinematic distributions of cluster galaxies in a ΛCDM cosmology. We investigate how the star formation rates (SFRs), colours and morphologies of galaxies vary as a function of distance from the cluster centre, and compare our results...

We use numerical simulations of a (480 Mpc h(-1))(3) volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev-Zeldovich (SZ) effects will be highly non-Gaussian, and very different from the peak-height distribution of a Gaussian random field. We then show that it is a good a...

We write the correlation function of dark matter particles, ξ(r), as the sum of two terms – one which accounts for non-linear evolution, and dominates on small scales, and another which is essentially the term from linear theory, and dominates on large scales. We use models of the number and spatial distribution of haloes and halo density profiles...

A model for the formation and evolution of structure in the Universe through the hierarchical assembly of matter can successfully account for the large scale distribution of galaxies with different internal properties as morphology, color or star formation rate. The same model naturally produces the complex distribution of stellar populations obser...

We present a simple model for the shape of the distribution function of galaxy peculiar velocities. We show how both nonlinear and linear theory terms combine to produce a distribution which has an approximately Gaussian core with exponential wings. The model is easily extended to study how the statistic depends on the type of particle used to trac...

A simple model is described of how objects of different masses stream towards each other as they cluster gravitationally. The model shows how the mean streaming velocity of dark matter particles is related to the motions of the parent dark matter haloes. It also provides a reasonably accurate description of how the pairwise velocity dispersion of d...

We identify high-density regions of supercluster size in high-resolution n-body simulations of a representative volume of three cold dark matter universes. By assuming that (1) the density and peculiar velocities of baryons trace those of the dark matter and that (2) the temperature of plasma is proportional to the velocity dispersion of the dark m...

We analyse the redshift space topology and geometry of the nearby Universe by computing the Minkowski functionals of the Updated Zwicky Catalogue (UZC). The UZC contains the redshifts of almost 20,000 galaxies, is 96% complete to the limiting magnitude m_Zw=15.5 and includes the Center for Astrophysics (CfA) Redshift Survey (CfA2). From the UZC we...

For the first time, the combination of semi-analytic modelling of galaxy formation and N-body simulations of cosmic structure formation enables us to model, at the same time, both the photometric and the clustering properties of galaxies. Two Cold Dark Matter Universes provide a reasonable fit to the observed properties of galaxies, groups and clus...

We use a new redshift survey complete to mR ' 15:4 within 4:25 o from the center of the Coma cluster to measure the mass profile of the cluster to r 5:5h Gamma1 Mpc. We extend the profile to r 10h Gamma1 Mpc with a further sample complete to mR = 15:4 in 42% of the area within a 10 ffi radius and to mZw = 15:5 in the remaining area. Galaxies within...

This is the third paper in a series which combines N-body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a Cold Dark Matter model with either Omega_0=1 (tauCDM) or Omega_0=0.3 and Lambda=0.7 (Lambda...

In hierarchical cosmologies the evolution of galaxy clustering depends both on cosmological quantities such as Omega and Lambda, which determine how dark matter halos form and evolve, and on the physical processes - cooling, star formation and feedback - which drive the formation of galaxies within these merging halos. In this paper, we combine dis...

We introduce a new technique for following the formation and evolution of galaxies in cosmological N-body simulations. Dissipationless simulations are used to track the formation and merging of dark matter halos as a function of redshift. Simple prescriptions, taken directly from semi-analytic models of galaxy formation, are adopted for cooling, st...

Using high-resolution cosmological N-body simulations, we investigate the survival of dark matter satellites falling into larger haloes. Satellites preserve their identity for some time after merging. We compute their loss of mass, energy and angular momentum as they are dissolved by dynamical friction, tidal forces and collisions with other satell...

In hierarchical clustering, galaxy clusters accrete mass through the aggregation of smaller systems. Thus, the velocity field of the infall regions of clusters contains significant random motion superposed on radial infall. Because the purely spherical infall model does not predict the amplitude of the velocity field correctly, methods estimating t...

The redshift-space correlation function $\xi_s$ for projected galaxy separations $\simless 1h^{-1}$ Mpc can be expressed as the convolution of the real-space correlation function with the galaxy pairwise velocity distribution function (PVDF). An exponential PVDF yields the best fit to the $\xi_s$ measured from galaxy samples of different redshift s...

We use N-body/hydrodynamic simulations of collapsing rich galaxy groups to predict X-ray properties of compact groups. The model is consistent with the X-ray observations of a few compact groups and naturally explains the correlation between the spiral fraction and the velocity dispersion and crossing time observed in compact groups. The model pred...

Current research on the origin and evolution of active galaxies is comprehensively surveyed in this collaborative volume. Both of the proposed types of central activity - active galactic nuclei and starbursts - are analysed with a particular emphasis on their relationship to the large-scale properties of the host galaxy. The crucial question is wha...

We use complete redshift surveys to study the redshift neighborhoods of 38 Hickson compact groups (HCGs). Twenty-nine of these HCGs (76%) are embedded in rich looser systems which we call HCG associations. Analysis of the redshift neighborhood of HCGs outside the CfA survey suggests that most HCGs are embedded in more extended physical systems. Ric...

The small crossing time of compact groups of galaxies (t(sub cr)H(sub 0) approximately less than 0.02) makes it hard to understand why they are observable at all. Our dissipationless N-body simulations show that within a single rich collapsing group compact groups of galaxies continually form. The mean lifetime of a particular compact configuration...

We present numerical simulations with the aim of studying how the violent relaxation induced by a non-dissipative collapse in an N-body system acts on the redistribution of the specific angular momentum.