The Effect of Tidal Stripping on Composite Stellar Populations in Dwarf Spheroidal Galaxies

We use N-body simulations to study the effects of tides on the kinematical structure of satellite galaxies orbiting a Milky Way-like potential. Our work is motivated by observations of dwarf spheroidal galaxies in the Local Group, for which often a distinction is possible between a cold centrally concentrated metal rich and a hot, extended metal poor population. We find that an important attenuation of the initial differences in the distribution of the two stellar components occurs for orbits with small pericentric radii (r_per < 20 kpc). This is mainly due to: i) the loss of the gravitational support provided by the dark matter component after tidal stripping takes place, which forces a re-configuration of the luminous components, and ii) tides preferentially affect the more extended stellar component, leading to a net decrease in its velocity dispersion as a response for the mass loss, which thus shrinks the kinematical gap. We apply these ideas to the Sculptor and Carina dwarf spheroidals. Differences in their orbits might help to explain, under the assumption of similar initial configurations, why in the former a clear kinematical separation between metal poor and metal rich stars is apparent, while in Carina this segregation is significantly more subtle.Comment: 17 pages, 7 figures, Accepted for publication in Advances in Astronomy, special issue on "Dwarf-Galaxy Cosmology

Dark influences III. Structural characterization of minor mergers of dwarf galaxies with dark satellites

In the current concordance cosmology small halos are expected to be completely dark and can significantly perturb low-mass galaxies during minor merger interactions. These interactions may well contribute to the diversity of the dwarf galaxy population. Dwarf galaxies in the field are often observed to have peculiarities in their structure, morphology, and kinematics, as well as strong bursts of star formation without apparent cause. We aim to characterize the signatures of minor mergers of dwarf galaxies with dark satellites to aid their observational identification. We explore and quantify a variety of structural, morphological, and kinematic indicators of merging dwarf galaxies and their remnants using a suite of hydrodynamical simulations. The most sensitive indicators of mergers with dark satellites are large asymmetries in the gaseous and stellar distributions, enhanced central surface brightness and starbursts, and velocity offsets and misalignments between the cold gas and stellar components. In general, merging systems span a wide range of values of the most commonly used indicators, while isolated objects tend to have more confined values. Interestingly, we find in our simulations that a significantly off-centered burst of star formation can pinpoint the location of the dark satellite. Observational systems with such characteristics are perhaps the most promising for unveiling the presence of the hitherto, missing satellites.Comment: 9 pages, 7 figures. Accepted in A&

Realidades invisibilizadas: pobreza e impacto de la crisis a partir de una investigación feminista en el área metropolitana de Barcelona

This article sets out a critical feminist analysis of poverty and the economic crisis, based a quantitative qualitative research carried out in 2009 with 2,609 women in the Barcelona metropolitan area. it begins with a critical analysis of the concept of poverty, which challenges conventional methods of calculating the poverty rate. it also refers to several aspects of the invisible differential impact of the economic crisis on women, in terms of women’s unemployment and its quality, and a process of recasualization of women's work and increased obligations in care work. These impacts are shown with employment statistics and the conclusion of the research carried out by the surt foundation.El artículo plantea una crítica feminista al análisis de la pobreza y la crisis económica, a partir de una investigación cuantitativa y cualitativa realizada en 2009 con 2.609 mujeres del área metropolitana de barcelona. se parte de un análisis crítico del concepto de pobreza, que cuestiona los métodos convencionales de cálculo de la tasa de pobreza, y de diversos aspectos invisibilizados del impacto de la crisis económica en las mujeres, en términos de desempleo y de calidad del desempleo, reprecarización del trabajo femenino, y aumento del trabajo reproductivo. Estos impactos se muestran a partir de estadísticas de empleo y las conclusiones del estudio realizado por la fundació surt

Stellar feedback by radiation pressure and photoionization

The relative impact of radiation pressure and photoionization feedback from young stars on surrounding gas is studied with hydrodynamic radiative transfer (RT) simulations. The calculations focus on the single-scattering (direct radiation pressure) and optically thick regime, and adopt a moment-based RT-method implemented in the moving-mesh code AREPO. The source luminosity, gas density profile and initial temperature are varied. At typical temperatures and densities of molecular clouds, radiation pressure drives velocities of order ~20 km/s over 1-5 Myr; enough to unbind the smaller clouds. However, these estimates ignore the effects of photoionization that naturally occur concurrently. When radiation pressure and photoionization act together, the latter is substantially more efficient, inducing velocities comparable to the sound speed of the hot ionized medium (10-15 km/s) on timescales far shorter than required for accumulating similar momentum with radiation pressure. This mismatch allows photoionization to dominate the feedback as the heating and expansion of gas lowers the central densities, further diminishing the impact of radiation pressure. Our results indicate that a proper treatment of the impact of young stars on the interstellar medium needs to primarily account for their ionization power whereas direct radiation pressure appears to be a secondary effect. This conclusion may change if extreme boosts of the radiation pressure by photon trapping are assumed.Comment: 18 pages, 19 figures (main results presented in 13 pages, 10 figures; extended appendix for RT tests with extra 9 figures). Accepted for publication in MNRAS after tiny change

Efeitos de uso de terra e manejo em populações de Annona crassiflora Mart. no Cerrado

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Ecologia, Programa de Pós-Graduação em Ecologia, 2017.O Cerrado apresenta diversas espécies com potencial de utilização, e a Annona crassiflora Mart., ou araticum, é uma árvore com frutos destinados principalmente à alimentação por comunidades tradicionais. Para incentivar o seu uso e extrativismo sustentável, o objetivo deste trabalho foi conhecer o estado de conservação de suas populações. Para tanto, foi avaliada estrutura populacional e os fatores ambientais e antrópicos de influência nas densidades dos estágios de vida, definidos como plântulas, infantes, jovens e adultos. Foram estudadas 40 populações de A. crassiflora em diversos estados de conservação, sendo 29 em áreas de cerrado primário e de 11 em áreas convertidas para pastagem. As variações ambientais foram representadas por teor de argila e soma de bases trocáveis do solo, cobertura vegetal e altitude, e as intervenções antrópicas por índices de extrativismo, presença de gado e raleamento de vegetação arbórea. As populações tenderam a distribuição simétrica de indivíduos ao longo das classes de diâmetro, com maiores quantidades de indivíduos menores em áreas de cerrado. Pastagens apresentaram, em média, 47% menos indivíduos que em áreas de cerrado, com mais lacunas de indivíduos nas classes de diâmetro. Em geral, as populações têm poucos indivíduos nas menores classes de diâmetro, indicando rápida passagem do estágio de plântula, e uma alta permanência nas classes subsequentes de tamanho. As densidades populacionais de todas as classes de tamanho foram associadas negativamente à soma de bases trocáveis do solo e altitude, e positivamente ao extrativismo de frutos. Plântulas e infantes foram associadas negativamente ao raleamento e ao gado, enquanto para jovens e adultos não houve essa relação. Reduzir frequência e intensidade de raleamento e do gado e o plantio de mudas pode favorecer o recrutamento de plântulas. O extrativismo não é prejudicial e deve ser incentivado principalmente em áreas de pastagem que conectam remanescentes de áreas naturais.The Cerrado biome harbors many useful plant species. Among these, Annona crassiflora Mart, known as araticum, is a tree with fruits used for human feeding, mainly by traditional communities. To encourage its sustainable use and harvest, the objective of this work was to know the conservation status of its populations. Therefore, it was evaluated the population structure and the environmental and anthropic variables associated to the life stage densities, defined as seedlings, infants, juvenile and adults. For this, we studied 40 populations of A. crassiflora in different conservation conditions, being 29 in primary cerrado and 11 in areas converted to pasture. Soil characteristics of clay content and sum of exchangeable bases, plant cover and altitude represented environment variable, while indexes of extractivism, cattle and vegetation thinning represented anthropic interventions. Most populations showed symmetric distribution of the individuals, but there were more individual of smaller classes in cerrado areas. Pasture areas had on average 47% less plants then in the cerrado, and it presented more gaps through the diameter classes. In general, populations have low densities of individuals at the smaller diameter classes, indicating rapid passage of the seedling stage to subsequent stages, in which permanence is longer. All size classes plant density were negatively associated with sum of exchangeable bases and altitude, and positively with fruit harvest. Seedlings and infants associated negatively with vegetation thinning and cattle index, whereas juveniles and adults did not present the same relation. Reducing frequency and intensity of vegetation thinning and cattle may increase seedling recruitment to higher life stages as well as by planting new individual. As fruit harvest is not harmful, it may be promoted, principally in pasture areas that connect cerrado remnants

Design and Development of Widgets for a Corporate Security Application

Aquest projecte es lliura com a Treball Final del Grau d'Enginyeria Informàtica de la Facultat d'Informàtica de Barcelona. L'objectiu és posar en pràctica els coneixements adquirits durant l'especialitat d'enginyeria del Software. El projecte consisteix a dissenyar i desenvolupar widgets per a una aplicació móvil corporativa de seguretat que permet als usuaris interaccionar amb una de les funcionalitats principals de la aplicació, sempre mantenint la perspectiva de la seguretat i la usabilitat.This project is delivered as the Bachelor Thesis of the Informatics Engineering Degree of the Barcelona Faculty of Computer Science. The objective is to put into practice the knowledge acquired during the Software engineering specialty. The project consists of designing and developing widgets for a corporate security mobile application that allows users to interact with one of the main functionalities of the application, always maintaining the perspective of security and usability

A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE

The hierarchical structure formation model predicts that stellar halos should form, at least partly, via mergers. If this was a predominant formation channel for the Milky Way's halo, imprints of this merger history in the form of moving groups or streams should exist also in the vicinity of the Sun. Here we study the kinematics of halo stars in the Solar neighbourhood using the very recent first data release from the Gaia mission, and in particular the TGAS dataset, in combination with data from the RAVE survey. Our aim is to determine the amount of substructure present in the phase-space distribution of halo stars that could be linked to merger debris. To characterise kinematic substructure, we measure the velocity correlation function in our sample of halo (low metallicity) stars. We also study the distribution of these stars in the space of energy and two components of the angular momentum, in what we call "Integrals of Motion" space. The velocity correlation function reveals substructure in the form of an excess of pairs of stars with similar velocities, well above that expected for a smooth distribution. Comparison to cosmological simulations of the formation of stellar halos indicate that the levels found are consistent with the Galactic halo having been built fully via accretion. Similarly, the distribution of stars in the space of "Integrals of motion" is highly complex. A strikingly high fraction (between 58% and upto 73%) of the stars that are somewhat less bound than the Sun are on (highly) retrograde orbits. A simple comparison to Milky Way-mass galaxies in cosmological hydrodynamical simulations suggests that less than 1% have such prominently retrograde outer halos. We also identify several other statistically significant structures in "Integrals of Motion" space that could potentially be related to merger events.Comment: 19 pages, 16 figures. A&A in pres