119183957
The environmental dependence of the red galaxy sequence
The dependence of the sequence of red galaxies (RS) with the environment is investigated using volume-limited samples of field, group and cluster galaxies drawn from the Sloan Digital Sky Survey. Our work focuses on studying the mean colour (μ R ) and the scatter (σ R ) of the RS as a function of 0.1 r-band absolute magnitude in different environments characterized either by the mass of the system in which the galaxies are located or by the distance to the system's centre. These results are compared with the RS of field galaxies. The same analysis is carried out using subsamples of red galaxies classified as early types according to their concentration parameter. For a given luminosity, μ R of field galaxies is bluer and σ R is larger than their group and cluster counterparts irrespective of mass and position within the systems. Among systems of galaxies, high-mass groups and clusters have the reddest μ R and the smallest σ R . These differences almost disappear when red early-type galaxies alone are considered. Galaxies in the core and in the outskirts of groups have similar μ R , whereas galaxies in clusters show a strong dependence on cluster-centric distance, the inner galaxies being the reddest objects. Red early-type galaxies in the outskirts of clusters have σ R values as large as those of field galaxies, while galaxies in the inner regions of clusters have lower values, comparable to those of group galaxies. We find that bright red early-type galaxies have reached nearly the same evolutionary stage in all environments. Our results suggest that, although effective in drifting galaxies of intermediate luminosities towards redder colours, the cluster environment is not necessary to populate the RS. We propose a scenario in which the RS in massive systems is populated by two different star formation history galaxies: red early-type galaxies that formed the bulk of their stars during the early stages of massive halo assembly and red galaxies that passed most of their lives inhabiting poor groups or the field and fell into massive systems at lower redshifts.
17723357
Galaxy groups in the 2dF Galaxy Redshift Survey: luminosity and mass statistics
Several statistics are applied to groups and galaxies in groups in the Two degree Field Galaxy Redshift Survey. Firstly we estimate the luminosity functions for different subsets of galaxies in groups. The results are well fitted by a Schechter function with parameters M ∗ 5log(h) = 19.90 ± 0.03 and � = 1.13 ± 0.02 for all galaxies in groups, which is quite consistent with the results by Norberg et al. for field galaxies. When considering the four different spectral types defined by Madgwick et al. we find that the characteristic magnitude is typically brighter than in the field. We also observe a steeper value, � = 0.76± 0.03, of the faint end slope for low star-forming galaxies when compared with the corresponding field value. This steepening is more conspicuous, � = 1.10 ± 0.06, for those galaxies in more massive groups (M � 10 14 h −1 M⊙) than the obtained in the lower mass subset, � = 0.71 ± 0.04 (M < 10 14 h −1 M⊙). Secondly, we compute group total luminosities using Moore, Frenk & White prescriptions. We define a flux-limited group sample using a new statistical tool developed by Rauzy. The resulting group sample is used to determine the group luminosity function finding a good agreement with previous determinations and semianalytical models.
17504603
Using the large scale quasar clustering to constrain flat quintessential universes
Aims. We search for the most suitable set of cosmological parameters that describes the observable universe. The search includes the possibility of quintessential flat universes, i.e., the analysis is restricted to the determination of the dimensionless matter density and the quintessential parameters, $\Omega_{\rm M}$ and w Q , respectively. Methods. Our study is focused on comparing the position of features at large scales in the density fluctuation field at different redshifts by analysing the evolution of the quasar two-point correlation function. We trace the density field fluctuations at large scales using a large and homogeneous sample of quasars (~38 000 objects with 0.3  ≲ z ≤  2.4 and a median z = 1.45) drawn from the Sloan Digital Sky Survey Data Release Six. The analysis relies on the assumption that, in the linear regime, the length scale of a particular feature should remain fixed at different times of the universe for the proper cosmological model. Our study does not assume any particular comoving length scale at which a feature should be found, but intends to perform a comparison for a wide range of scales instead. This is done by quantifying the amount of overlap among the quasar correlation functions at different times using a cross-correlation technique. Results. The most likely cosmological model is $\Omega_{\rm M}$ = 0.21 ± 0.02 and w Q = -0.93 ± 0.04, in agreement with previous studies. These constraints are the result of a good overall agreement of the correlation function at different redshifts over scales ~100–300 h -1 Mpc. Conclusions. Under the assumption of a flat cosmological model, our results indicate that we are living in a low density universe with a quintessential parameter greater than the one corresponding to a cosmological constant. This work also demonstrates that a large homogeneous quasar sample can be used to tighten the constraints upon cosmological parameters.
117908138
COMPARING GALAXY POPULATIONS IN COMPACT AND LOOSEGROUPS OF GALAXIES
Aims. We compare the properties of galaxies in compact groups, loose groups, and the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. Methods. We select samples of galaxies in compact groups, loose groups, and field galaxies from the Sloan Digital Sky Survey. We compare the properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass, and concentration. We also study the fraction of red and early-type galaxies, the luminosity function, the colourluminosity, and luminosity-size relations. Results. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of red and early-type galaxies is larger in compact groups. Galaxies in compact groups are, on average, systematically smaller in size, more concentrated, and have higher surface brightnesses than galaxies in the field and in loose groups. At a fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller in size. Conclusions. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups, owing to the typically high densities and small velocity dispersions of these environments, which could explain the large fraction of red and early-type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.
16676496
Clustering and Light Profiles of Galaxies in the Environment of 20 Ultra-Steep-Spectrum Radio Sources
We have analyzed galaxy properties in the neighborhood of 20 ultra–steep-spectrum (USS) radio sources taken from the Westerbork in the Southern Hemisphere (WISH) catalog of De Breuck and coworkers. Galaxies in these USS fields were identified in deep observations that were carried out in the K' band using the OSIRIS imager at the CTIO 4 m telescope. We find a statistically significant signal of clustering around our sample of USS sources. The angular extension of the detected USS source–galaxy clustering is θc ~ 20'', corresponding to a spatial scale of ~120 h-1 kpc, assuming the sources are at z ~ 1 in an Ωm = 0.3, ΩΛ = 0.7 model universe. These results are in agreement with those obtained by Best for radio galaxy–galaxy correlation, and Best and coworkers for radio-loud AGN–galaxy correlation. We have also analyzed the light distribution of the galaxies by fitting Sersic's law profiles. Our results show no significant dependence of the galaxy shape parameters on the projected distance to the USS source.
118549208
An analytic Pade-motivated QCD coupling
We consider a modification of the Minimal Analytic (MA) coupling of Shirkov and Solovtsov. This modified MA (mMA) coupling reflects the desired analytic properties of the space‐like observables. We show that an approximation by Dirac deltas of its discontinuity function ρ is equivalent to a Pade (rational) approximation of the mMA coupling that keeps its analytic structure. We propose a modification to mMA that, as preliminary results indicate, could be an improvement in the evaluation of low‐energy observables compared with other analytic couplings.
118070287
Cosmology, Relativity and Cosmic Rays
This is a short review of the evolution of ideas and concepts about the Universe. It is based on the introductory talk given on the 25 of July 2008 within the Third School on Cosmic Rays and Astrophysics held in Arequipa, Peru.
122967003
Augmented reality aiding collimator exchange at the LHC
Novel Augmented Reality techniques have the potential to have a large positive impact on the way remote maintenance operations are carried out in hazardous areas, e.g. areas where radiation doses that imply careful planning and optimization of maintenance operations are present. This paper describes an Augmented Reality strategy, system and implementation for aiding the remote collimator exchange in the LHC, currently the world׳s largest and highest-energy particle accelerator. The proposed system relies on marker detection and multi-modal augmentation in real-time. A database system has been used to ensure flexibility. The system has been tested in a mock-up facility, showing real time performance and great potential for future use in the LHC. The technical-scientific difficulties identified during the development of the system and the proposed solutions described in this paper may help the development of future Augmented Reality systems for remote handling in scientific facilities.
122910167
Implications of Yukawa textures in the neutral Higgs decays within the 2HDM–III
We discuss the implications of assuming a four–zero Yukawa ansatz for the neutral Higgs decays, within the context of the general 2–Higgs Doublet Model of type III. We begin by presenting a detailed analysis of the neutral Higgs boson couplings with fermions and gauge bosons and the resulting effects on its decays. In particular, we are interested on the possibility of the neutral Higgs boson production in current colliders.
56302496
Design, analysis, and fabrication of the APT cavities
The design for the superconducting cavities of the high-energy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.
14875226
Galaxy groups in the 2dF Galaxy Redshift Survey: a compactness analysis of groups
A comprehensive study on compactness has been carried out on the 2dF Galaxy Group Catalogue constructed by Merchan and Zandivarez. The compactness indices defined in this work take into account different geometrical constraints in order to explore a wide range of possibilities. Our results show that there is no clear distinction between groups with high and low levels of compactness when considering particular properties such as the radial velocity dispersion, the relative fraction of galaxies per spectral type, and the luminosity functions of their galaxy members. Studying the trend of the fraction of galaxies per spectral type as a function of the dimensionless crossing time, some signs of dynamical evolution are observed. From the comparison with previous works on compactness, we realize that special care should be taken for some compactness criteria definitions in order to avoid possible biases in the identification.