Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos

We study the population of satellite galaxies formed in a suite of N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find little spatial or kinematic bias between the dark matter and the satellite population. The velocity dispersion of the satellites is a good indicator of the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the rotation speed of their disk components. The detailed kinematics of simulated satellites and dark matter are also in good agreement. By contrast, the stellar halo of the simulated galaxies is kinematically and spatially distinct from the population of surviving satellites. This is because the survival of a satellite depends on mass and on time of accretion; surviving satellites are biased toward low-mass systems that have been recently accreted by the galaxy. Our results support recent proposals for the origin of the systematic differences between stars in the Galactic halo and in Galactic satellites: the elusive ``building blocks'' of the Milky Way stellar halo were on average more massive, and were accreted (and disrupted) earlier than the population of dwarfs that has survived self-bound until the present.Comment: 13 pages, 11 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme Orbits

We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of $L_*$ galaxies in a LCDM universe. Most satellites follow conventional orbits; after turning around, they accrete into their host halo and settle on orbits whose apocentric radii are steadily eroded by dynamical friction. However, a number of outliers are also present, we find that ~1/3 of satellites identified at $z=0$ are on unorthodox orbits, with apocenters that exceed their turnaround radii. This population of satellites on extreme orbits consists typically of the faint member of a satellite pair that has been ejected onto a highly-energetic orbit during its first approach to the primary. Since the concurrent accretion of multiple satellite systems is a defining feature of hierarchical models of galaxy formation, we speculate that this three-body ejection mechanism may be the origin of (i) some of the newly discovered high-speed satellites around M31 (such as Andromeda XIV); (ii) some of the distant fast-receding Local Group members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus and Tucana in the outskirts of the Local Group. Our results suggest that care must be exercised when using the orbits of the most weakly bound satellites to place constraints on the total mass of the Local Group.Comment: 10 pages, 6 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Density distribution of particles upon jamming after an avalanche in a 2D silo

We present a complete analysis of the density distribution of particles in a two dimensional silo after discharge. Simulations through a pseudo-dynamic algorithm are performed for filling and subsequent discharge of a plane silo. Particles are monosized hard disks deposited in the container and subjected to a tapping process for compaction. Then, a hole of a given size is open at the bottom of the silo and the discharge is triggered. After a clogging at the opening is produced, and equilibrium is restored, the final distribution of the remaining particles at the silo is analyzed by dividing the space into cells with different geometrical arrangements to visualize the way in which the density depression near the opening is propagated throughout the system. The different behavior as a function of the compaction degree is discussed.Comment: 11 pages, 10 figure

Avaliação do desempenho produtivo de bovinos de corte, em pastos puros e consorciados com o amendoim forrageiro cultivar Mandobi, no Acre.

Objetivou-se avaliar o efeito da consorciação de pastos de Brachiaria humidicola com Arachis pintoi cv. Mandobi sobre o desempenho produtivo de novilhos Nelore. O experimento foi realizado em uma fazenda particular no Estado do Acre, de novembro de 2013 a fevereiro de 2014. As unidades experimentais foram seis piquetes de 1,42 ha cada, em um delineamento inteiramente casualizado, com dois tratamentos e três repetições. Foram utilizados seis novilhos Nelore, não castrados, com idade e peso médio iniciais de 16 meses e 282 kg, como testes. Novilhos adicionais foram alocados ou retirados dos piquetes para a manutenção da altura do pasto, em 15 cm. Os animais foram pesados a cada 28 dias, após um jejum de 16 horas, para determinar o ganho de peso médio diário (GMD). A capacidade de suporte foi calculada de acordo com o peso médio e número de animais/dia em cada unidade experimental. A produtividade animal foi calculada com base no GMD dos animais teste e o número de animais/dia utilizados durante todo experimento. As médias dos quadrados mínimos foram comparadas usando o teste de Tukey com 5% de probabilidade. A taxa de lotação durante o período experimental foi de 3,97 UA/ha nos pastos consorciado e 3,81 nos pastos puros (P = 0,8255). O ganho de peso médio diário dos animais foi 17,7% superior (P = 0,0465) para o pasto consorciado (0,597 x 0,479 kg/animal/dia) e a produtividade animal aumentou 18,7% (P = 0,1010) pelo uso de A. pintoi cv. Mandobi (330 kg/ha x 278 kg/ha). Este estudo mostra que apenas 7,7% desta leguminosa em pastagens consorciadas com Brachiaria humidicola pode afetar positivamente a produtividade animal

Newly arrived migrant and refugee children in the British educational system

In 2009, Action for Social Integration was commissioned by London Councils to implement a four-year programme to improve the educational attainment for African and Caribbean children and young people in Barnet, Enfield and Haringey. Within this programme, the Social Policy Research Centre (SPRC) at Middlesex University has carried out a small-scale research project aimed at producing a guide for BME and migrant parents of children attending UK schools. The guide provides information to better understand the UK educational system, highlighting what may be different from those of other countries in the world and discussing issues such as language support and parents’ involvement. In order to identify the knowledge gaps and the main issues to include in the guide, the research team conducted a series of interviews, as well as an analysis and mapping of existing demographic data. The research findings presented in this report contribute to a better understanding of the key challenges and opportunities facing BME parents and their children in London schools

Forgotten Irish

The research was commissioned by the Ireland Fund of Great Britain to inform its Forgotten Irish Campaign and decisions about where to deploy funds most effectively. It aimed to identify groups of Irish people who have experienced problems settling in Britain but who, for personal or economic reasons, are reluctant or unable to return to Ireland. They may be isolated and lack support in Britain, especially as they get older, but have little contact with family in Ireland. It is this group which has become the focus of the Forgotten Irish Campaign. The research used a range of evidence – from national statistics, local research reports and key informant interviews – to identify particular groups who suffer disadvantage and specific issues which disproportionately affect the Irish population. Some of these groups – such as single elderly men – are well known to organisations working with the Irish community. The research provides further evidence of the inter-related problems which they face. The research also uncovered evidence of other problems which particularly affect the Irish population in Britain and of groups within the Irish community who face specific difficulties but whose needs are not widely acknowledged either by mainstream service providers or by Irish services

Satellite Galaxies and Fossil Groups in the Millennium Simulation

We use a semianalytic galaxy catalogue constructed from the Millennium Simulation to study the satellites of isolated galaxies in the LCDM cosmogony. This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites) allows the characterization, with minimal statistical uncertainty, of the dynamical properties of satellite/primary galaxy systems in a LCDM universe. We find that, overall, the satellite population traces the dark matter rather well: its spatial distribution and kinematics may be approximated by an NFW profile with a mildly anisotropic velocity distribution. Their spatial distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg'' effect that reflects the misalignment between the major axis and angular momentum of the host halo. The isolation criteria for our primaries picks not only galaxies in sparse environments, but also a number of primaries at the centre of ''fossil'' groups. We find that the abundance and luminosity function of these unusual systems are in reasonable agreement with the few available observational constraints. We recover the expected L_{host} \sigma_{sat}^3 relation for LCDM models for truly-isolated primaries. Less strict primary selection, however, leads to substantial modification of the scaling relation. Our analysis also highlights a number of difficulties afflicting studies that rely on blind stacking of satellite systems to constrain the mean halo mass of the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms

In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein modes; yet only for the Eu and Sr systems is there a large dip in the thermal conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here we argue that it is the off-center displacement that is crucial for understanding this unexplained difference in behavior. It enhances the coupling between the "rattler" motion and the lattice phonons for the Eu and Sr systems, and turns on/off another scattering mechanism (for 1K < T < 20K) produced by the presence/absence of off-center sites. The random occupation of different off-center sites produces a high density of symmetry-breaking defects which scatters phonons. It may also be important for improving our understanding of other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened arguments regarding need for additional phonon scattering mechanis