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This paper is based on the multi-band VST Early-type GAlaxy Survey (VEGAS) with the VLT Survey Telescope (VST). We present new deep photometry of the IC1459 group in g and r band. The main goal of this work is to investigate the photometric properties of the IC1459 group, and to compare our results with those obtained for other galaxy groups studied in VEGAS, in order to provide a first view of the variation of their properties as a function of the evolution of the system. For all galaxies in the IC1459 group, we fit isophotes and extract the azimuthally-averaged surface-brightness profiles, the position angle and ellipticity profiles as a function of the semi-major axis, as well as the average colour profile. In each band, we estimate the total magnitudes, effective radii, mean colour, and total stellar mass for each galaxies in the group. Then we look at the structure of the brightest galaxies and faint features in their outskirts, considering also the intragroup component. The wide field of view, long integration time, high angular resolution, and arcsec-level seeing of OmegaCAM@VST allow us to map the light distribution of IC1459 down to a surface brightness level of 29.26 mag arcsec^{-2} in g band and 28.85 mag arcsec^{-2} in r band, and out to 7-10 Re, and to detect the optical counterpart of HI gas around IC1459. We also explore in depth three low density environments and provide information to understand how galaxies and groups properties change with the group evolution stage. There is a good agreement of our results with predictions of numerical simulations regarding the structural properties of the brightest galaxies of the groups. We suggest that the structure of the outer envelope of the BCGs, the intra-group light and the HI amount and distribution may be used as indicators of the different evolutionary stage and mass assembly in galaxy groups., Comment: Accepted for publication in Astronomy & Astrophysics

In recent years, multiple studies have reported substantial populations of large, low-surface-brightness galaxies in local galaxy clusters. Various theories that aim to explain the presence of such ultra-diffuse galaxies (UDGs) have since been proposed. A key question that will help to differentiate between models is whether UDGs have counterparts in lower-mass host haloes, and what their abundance as a function of halo mass is. In this study we extend our previous study of UDGs in galaxy clusters to galaxy groups. We measure the abundance of UDGs in 325 spectroscopically-selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make use of the overlapping imaging from the ESO Kilo-Degree Survey (KiDS), from which we can identify galaxies with mean surface brightnesses within their effective radii down to ~25.5 mag arcsec$^{-2}$ in the r-band. We are able to measure a significant overdensity of UDGs (with sizes r_eff > 1.5 kpc) in galaxy groups down to M200=10^12 Msun, a regime where approximately only 1 in 10 groups contains a UDG that we can detect. We combine measurements of the abundance of UDGs in haloes that cover three orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass; N_UDG (R, Comment: 13 pages, 9 figures (including appendices). Accepted for publication in A&A after minor revision

Semi-analytic models (SAMs) are currently one of the primary tools with which we model statistically significant ensembles of galaxies. The underlying physical prescriptions inherent to each SAM are, in many cases, different from one another. Several SAMs have been applied to the dark matter merger trees extracted from the Millennium Run, including those associated with the well-known Munich and Durham lineages. We compare the predicted luminosity distributions of galaxy groups using four publicly available SAMs, in order to explore a galactic environment in which the models have not been explored to the same degree as they have in the field or in rich clusters. We identify a characteristic 'wiggle' in the group galaxy luminosity function generated using the De Lucia et al. SAM, which is not present in the Durham-based models, consistent to some degree with observations. However, a comparison between conditional luminosity functions of groups between the models and observations suggests that neither model is a particularly good match. The luminosity function wiggle is interpreted as the result of the two-mode active galactic nucleus feedback implementation used in the Munich models, which itself results in flattened magnitude gap distribution. An associated analysis of the magnitude gap distribution between first-and second-ranked group galaxies shows that while the Durham models yield distributions with approximately equal luminosity first-and second-ranked galaxies, in agreement with observations, the De Lucia et al. models favour the scenario in which the second-ranked galaxy is approximately 1 mag fainter than the primary, especially when the dynamic range of the mock data is limited to 3 mag.

This paper is devoted to the analysis of charged superselection sectors in the framework of the locally covariant quantum field theories. We shall analize sharply localizable charges, and use net-cohomology of J.E. Roberts as a main tool. We show that to any 4-dimensional globally hyperbolic spacetime it is attached a unique, up to equivalence, symmetric tensor $\Crm^*-$category with conjugates (in case of finite statistics); to any embedding between different spacetimes, the corresponding categories can be embedded, contravariantly, in such a way that all the charged quantum numbers of sectors are preserved. This entails that to any spacetime is associated a unique gauge group, up to isomorphisms, and that to any embedding between two spacetimes there corresponds a group morphism between the related gauge groups. This form of covariance between sectors also brings to light the issue whether local and global sectors are the same. We conjecture this holds that at least on simply connected spacetimes. It is argued that the possible failure might be related to the presence of topological charges. Our analysis seems to describe theories which have a well defined short-distance asymptotic behaviour., 66 pages

In this paper, we study gravitational lensing by groups of galaxies. Since groups are abundant and therefore have a large covering fraction on the sky, lensing by groups is likely to be very important observationally. Besides, it has recently become clear that many lens models for strong lensing by individual galaxies require external shear to reproduce the observed image geometries; in many cases a nearby group is detected that could provide this shear. In this work, we study the expected lensing behavior of galaxy groups in both the weak and strong lensing regime. We examine the shear and magnification produced by a group and its dependence on the detailed mass distribution within the group. We find that the peak value of the weak lensing shear signal is of the order of 3 per cent and varies by a factor of about 2 for different mass distributions. These variations are large enough to be detectable in the Sloan Digital Sky Survey (SDSS). In the strong lensing regime we find that the image geometries and typical magnifications are sensitive to the group properties and that groups can easily provide enough external shear to produce quadruple images. We investigate the statistical properties of lensing galaxies that are near or part of a group and find that statistical lens properties, like the distribution of time delays, are affected measurably by the presence of the group which can therefore introduce an additional systematic error in the measurement of the Hubble constant from such systems. We conclude that both the detection of weak lensing by groups and accurate observations of strong galaxy lens systems near groups could provide important information on the total mass and matter distribution within galaxy groups., Comment: 40 pages, 12 figures + 2 color figs (high resolution color figures available at http://www.astro.rug.nl/~ole/groups/highres/), submitted to ApJ

We present mass models of the four-image gravitational lens system B1608 + 656, based on information obtained through VLBA imaging, VLA monitoring, and Hubble Space Telescope (HST) WFPC2 and NICMOS imaging. We have determined a mass model for the lens galaxies that reproduces (1) all image positions within the observational errors, (2) two out of three flux-density ratios within about 10% from the observed ratios, and (3) the model time delays within 1% from their observed values, given our best estimate of the Hubble parameter. Using the time delays determined in a companion paper, we also find that the best isothermal mass model gives H-0 = 59(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 1 and Omega(Lambda) = 0.0, or H-0 = (65-63)(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. The statistical errors indicate the 95.4% (2 sigma) confidence interval. A systematic error of +/-15 km s(-1) Mpc(-1) is estimated from a 20% (1 sigma) uncertainty in the steepness of radial mass profile. This cosmological determination of H-0 agrees well with determinations from three other gravitational lens systems (i.e., B0218 + 357, Q0957 + 561, and PKS 1830-211), Type Ia supernovae, the Sunyaev-Zeldovich effect and local determinations. The current agreement on H-0-within the 1 sigma statistical errors-from four of five gravitational lens systems (1) emphasizes the reliability of its determination from isolated gravitational lens systems and (2) suggests that a close-to-isothermal mass profile can describe disk galaxies (e.g., B0218 + 357 and possibly PKS 1830-211), ellipticals (e.g., B1608 +/- 656), and central cluster ellipticals (e.g., 00957 + 561). The average of H-0 from B0218 + 357, Q0957 + 561, B1608 + 656, and PKS 1830-211, gives H-0(GL) = 69 +/- 7 km s(-1) Mpc(-1) for a flat universe with Omega(m) = 1 or H-0(GL) = 74 +/- 8 km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. When including PG 1115 + 080, these values decrease to 64 +/- 11 km s(-1) Mpc(-1) and 68 +/- 13 km s(-1) Mpc(-1), respectively. The errors are the estimated 2 a errors on the average. The Hubble parameter from gravitational lenses seems to agree best with local determinations of H-0 for a low-density universe, under the assumption that all lenses are nearly isothermal.

We discuss the results of a VLA(2) [Napier et al., Proc. IEEE 71, 1295 (1983)] H I survey of the Bootes void and compare the distribution and H I properties of the void galaxies to those of galaxies found in a survey of regions of mean cosmic density. The Bootes survey covers 1100 Mpc(3), or similar to 1% of the volume of the void and consists of 24 cubes of typically 2 MpcX2 MpcX1280 km s(-1), centered on optically known galaxies. Sixteen targets were detected in H I; 18 previously uncataloged objects were discovered directly in H I. The control samples consists of 12 cubes centered on IRAS-selected galaxies with FIR luminosities similar to those of the Bootes targets and located in regions of one to two times the cosmic mean density. In addition to the 12 targets 29 companions were detected in H I. We find that the number of galaxies within 1 Mpc of the targets is the same to within a factor of 2 for void and control samples, and thus that the small scale clustering of galaxies is the same in regions that differ by a factor of similar to 6 in density an larger scales. A dynamical analysis of the galaxies in the void suggests that on scales of a few Mpc the galaxies are gravitationally bound, forming interacting galaxy pairs, loose pairs, and loose groups. One group is compact enough to qualify as a Hickson compact group (hereafter referred to as HCG [Hickson, APJ, 255, 382 (1952)]. The galaxies found in the void are mostly late-type, gas-rich systems. A careful scrutiny of their H I and optical properties shows them to be very similar to field galaxies of the same morphological type. This, combined with our finding that the small scale clustering of the galaxies in the voids is the same as in the field, suggests that it is the near environment that mostly affects the evolution of galaxies. (C) 1996 American Astronomical Society.

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved, Semi-analytic models (SAMs) are currently one of the primary tools with which we model statistically significant ensembles of galaxies. The underlying physical prescriptions inherent to each SAM are, in many cases, different from one another. Several SAMs have been applied to the dark matter merger trees extracted from the Millennium Run, including those associated with the well-known Munich and Durham lineages. We compare the predicted luminosity distributions of galaxy groups using four publicly available SAMs, in order to explore a galactic environment in which the models have not been explored to the same degree as they have in the field or in rich clusters. We identify a characteristic 'wiggle' in the group galaxy luminosity function generated using the De Lucia et al. SAM, which is not present in the Durham-based models, consistent to some degree with observations. However, a comparison between conditional luminosity functions of groups between the models and observations suggests that neither model is a particularly good match. The luminosity function wiggle is interpreted as the result of the two-mode active galactic nucleus feedback implementation used in the Munich models, which itself results in flattened magnitude gap distribution. An associated analysis of the magnitude gap distribution between first- and second-ranked group galaxies shows that while the Durham models yield distributions with approximately equal luminosity first- and second-ranked galaxies, in agreement with observations, the De Lucia et al. models favour the scenario in which the second-ranked galaxy is approximately 1 mag fainter than the primary, especially when the dynamic range of the mock data is limited to 3 mag., ONS acknowledges the support of the STFC through its PhD Studentship Programme. BKG and CBB acknowledge the support of the UK Science & Technology Facilities Council (STFC Grant ST/F002432/1) and the Commonwealth Cosmology Initiative; visitor support (PS-B, DK, AK and LVS) from the STFC (ST/G003025/1) is similarly acknowledged. PS-B acknowledges the support of a Marie Curie Intra-European Fellowship within the 6th European Community Framework Programme. AK and PS-B are supported by the Ministerio de Ciencia e Innovación (MICINN) in Spain through the Ramón y Cajal programme. The Millennium Simulation data bases used in this paper and the web application providing online access to them were constructed as part of the activities of the German Astrophysical Virtual Observatory. Access to the University of Central Lancashire’s High Performance Computing Facility is gratefully acknowledged. We acknowledge the computational support provided by the UK National Cosmology Supercomputer, COSMOS. We thank the DEISA consortium, cofunded through EU FP6 project RI-031513 and the FP7 project RI-222919, for support within the DEISA Extreme Computing Initiative

We characterize the automorphisms of aC*-algebra Open image in new window which extend to automorphisms of the crossed product Open image in new window by a compact group dual. The case where the inclusion Open image in new window is equipped with a group of automorphisms commuting with the dual action is also treated. These results are applied to the analysis of broken gauge symmetries in Quantum Field Theory to draw conclusions on the structure of the degenerate vacua on the field algebra.

We introduce and investigate the notion of a quasi-complete group. A group G is quasi-complete if every automorphism f A AutðGÞ, with the property that p and pf are uni- tarily equivalent for every unitary irreducible representation p of G, is an inner automorphism of G. Our main result is that every connected linear real reductive Lie group is quasi-complete.

We present mass models of the four-image gravitational lens system B1608 + 656, based on information obtained through VLBA imaging, VLA monitoring, and Hubble Space Telescope (HST) WFPC2 and NICMOS imaging. We have determined a mass model for the lens galaxies that reproduces (1) all image positions within the observational errors, (2) two out of three flux-density ratios within about 10% from the observed ratios, and (3) the model time delays within 1% from their observed values, given our best estimate of the Hubble parameter. Using the time delays determined in a companion paper, we also find that the best isothermal mass model gives H-0 = 59(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 1 and Omega(Lambda) = 0.0, or H-0 = (65-63)(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. The statistical errors indicate the 95.4% (2 sigma) confidence interval. A systematic error of +/-15 km s(-1) Mpc(-1) is estimated from a 20% (1 sigma) uncertainty in the steepness of radial mass profile. This cosmological determination of H-0 agrees well with determinations from three other gravitational lens systems (i.e., B0218 + 357, Q0957 + 561, and PKS 1830-211), Type Ia supernovae, the Sunyaev-Zeldovich effect and local determinations. The current agreement on H-0-within the 1 sigma statistical errors-from four of five gravitational lens systems (1) emphasizes the reliability of its determination from isolated gravitational lens systems and (2) suggests that a close-to-isothermal mass profile can describe disk galaxies (e.g., B0218 + 357 and possibly PKS 1830-211), ellipticals (e.g., B1608 +/- 656), and central cluster ellipticals (e.g., 00957 + 561). The average of H-0 from B0218 + 357, Q0957 + 561, B1608 + 656, and PKS 1830-211, gives H-0(GL) = 69 +/- 7 km s(-1) Mpc(-1) for a flat universe with Omega(m) = 1 or H-0(GL) = 74 +/- 8 km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. When including PG 1115 + 080, these values decrease to 64 +/- 11 km s(-1) Mpc(-1) and 68 +/- 13 km s(-1) Mpc(-1), respectively. The errors are the estimated 2 a errors on the average. The Hubble parameter from gravitational lenses seems to agree best with local determinations of H-0 for a low-density universe, under the assumption that all lenses are nearly isothermal.

We discuss the results of a VLA(2) [Napier et al., Proc. IEEE 71, 1295 (1983)] H I survey of the Bootes void and compare the distribution and H I properties of the void galaxies to those of galaxies found in a survey of regions of mean cosmic density. The Bootes survey covers 1100 Mpc(3), or similar to 1% of the volume of the void and consists of 24 cubes of typically 2 MpcX2 MpcX1280 km s(-1), centered on optically known galaxies. Sixteen targets were detected in H I; 18 previously uncataloged objects were discovered directly in H I. The control samples consists of 12 cubes centered on IRAS-selected galaxies with FIR luminosities similar to those of the Bootes targets and located in regions of one to two times the cosmic mean density. In addition to the 12 targets 29 companions were detected in H I. We find that the number of galaxies within 1 Mpc of the targets is the same to within a factor of 2 for void and control samples, and thus that the small scale clustering of galaxies is the same in regions that differ by a factor of similar to 6 in density an larger scales. A dynamical analysis of the galaxies in the void suggests that on scales of a few Mpc the galaxies are gravitationally bound, forming interacting galaxy pairs, loose pairs, and loose groups. One group is compact enough to qualify as a Hickson compact group (hereafter referred to as HCG [Hickson, APJ, 255, 382 (1952)]. The galaxies found in the void are mostly late-type, gas-rich systems. A careful scrutiny of their H I and optical properties shows them to be very similar to field galaxies of the same morphological type. This, combined with our finding that the small scale clustering of the galaxies in the voids is the same as in the field, suggests that it is the near environment that mostly affects the evolution of galaxies. (C) 1996 American Astronomical Society.