Escenarios cosmológicos con distintos parámetros de densidad

Se están analizando diferentes escenarios cosmológicos con distintos parámetros de densidad compatibles con las determinaciones del espectro primordial de fluctuaciones, el contenido de material bariónico en cúmulos de galaxias y los resultados de la teoría de nucleosíntesis, el campo de velocidades peculiares de galaxias y su distribución espacial. Además, se está trabajando en la elaboración de un programa de cálculo de N-cuerpos basado en el esquema particle - mesh y que permite un tratamiento mas exacto de las interacciones partícula - partícula en escalas menores que la resolución numérica del potencial de la red.Asociación Argentina de Astronomí

Dependencia de la longitud de correlación de galaxias con el tipo morfológico y la velocidad circular

Utilizando el catálogo de velocidades radiales CfA investigamos la dependencia entre la longitud de correlación r. de galaxias con el tipo morfológico t y la velocidad circular Vc. Adoptando una ley de potencia para la función de correlación bipuntual x(r) =(r/r₀) con g = 1.8 y r₀ = 6 h Mpc (valor medio), se determina una relación entre r₀ y t que resulta: r₀ = (6.7 - 0.3 t) h Mpc. Encontramos una dependencia significativa entre el número medio de vecinos y la velocidad circular de las galaxias. Objetos con Vc mayor que 250 km/s presentan un exceso en el número medio de vecinos dentro de esferas de radio R, R < 6 h Mpc. Este exceso implica un incremento del 20% en el valor de r. respecto a su valor medio. Por otra parte no se encuentra evidencia estadística de una dependencia similar para objetos con velocidades Vc < 250 km/s.Asociación Argentina de Astronomí

Ring galaxies in the EAGLE hydrodynamical simulations

Galaxie

Indirect Dark Matter Detection from Dwarf Satellites: Joint Expectations from Astrophysics and Supersymmetry

We present a general methodology for determining the gamma-ray flux from annihilation of dark matter particles in Milky Way satellite galaxies, focusing on two promising satellites as examples: Segue 1 and Draco. We use the SuperBayeS code to explore the best-fitting regions of the Constrained Minimal Supersymmetric Standard Model (CMSSM) parameter space, and an independent MCMC analysis of the dark matter halo properties of the satellites using published radial velocities. We present a formalism for determining the boost from halo substructure in these galaxies and show that its value depends strongly on the extrapolation of the concentration-mass (c(M)) relation for CDM subhalos down to the minimum possible mass. We show that the preferred region for this minimum halo mass within the CMSSM with neutralino dark matter is ~10^-9-10^-6 solar masses. For the boost model where the observed power-law c(M) relation is extrapolated down to the minimum halo mass we find average boosts of about 20, while the Bullock et al (2001) c(M) model results in boosts of order unity. We estimate that for the power-law c(M) boost model and photon energies greater than a GeV, the Fermi space-telescope has about 20% chance of detecting a dark matter annihilation signal from Draco with signal-to-noise greater than 3 after about 5 years of observation

Pregnancy in women with perinatally acquired HIV-infection: Outcomes and challenges

This is a retrospective comparison of pregnant women with perinatally acquired HIV-infection (PAH) with a cohort of pregnant women with behaviorally acquired HIV-infection (BAH). PAH cases (11 women) included all pregnant adolescents followed at our HIV clinic from January 2000 to January 2009. BAH cases (27 women) were randomly selected from all deliveries within the study period at the same institution. Demographics, mode of delivery, CD4+ counts, and viral loads (VLs) before, during, and six months postpartum, as well as neonatal outcomes, were reviewed

Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons

We extract at redshift z=0 a Milky Way sized object including gas, stars and dark matter (DM) from a recent, high-resolution cosmological N-body simulation with baryons. Its resolution is sufficient to witness the formation of a rotating disk and bulge at the center of the halo potential. The phase-space structure of the central galactic halo reveals the presence of a dark disk component, that is co-rotating with the stellar disk. At the Earth's location, it contributes to around 25% of the total DM local density, whose value is rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations from pure Gaussian and Maxwellian distributions, with a sharper drop of the high velocity tail. We give a detailed study of the impact of these features on the predictions for DM signals in direct detection experiments. In particular, the question of whether the modulation signal observed by DAMA is or is not excluded by limits set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and compared to the case of a standard Maxwellian halo, in both the elastic and the inelastic scattering scenarios. We find that the compatibility between DAMA and the other experiments is improved. In the elastic scenario, the DAMA modulation signal is slightly enhanced in the so-called channeling region, as a result of several effects. For the inelastic scenario, the improvement of the fit is mainly attributable to the departure from a Maxwellian distribution at high velocity.Comment: 39 page

The outer halos of elliptical galaxies

Recent progress is summarized on the determination of the density distributions of stars and dark matter, stellar kinematics, and stellar population properties, in the extended, low surface brightness halo regions of elliptical galaxies. With integral field absorption spectroscopy and with planetary nebulae as tracers, velocity dispersion and rotation profiles have been followed to ~4 and ~5-8 effective radii, respectively, and in M87 to the outer edge at ~150 kpc. The results are generally consistent with the known dichotomy of elliptical galaxy types, but some galaxies show more complex rotation profiles in their halos and there is a higher incidence of misalignments, indicating triaxiality. Dynamical models have shown a range of slopes for the total mass profiles, and that the inner dark matter densities in ellipticals are higher than in spiral galaxies, indicating earlier assembly redshifts. Analysis of the hot X-ray emitting gas in X-ray bright ellipticals and comparison with dynamical mass determinations indicates that non-thermal components to the pressure may be important in the inner ~10 kpc, and that the properties of these systems are closely related to their group environments. First results on the outer halo stellar population properties do not yet give a clear picture. In the halo of one bright galaxy, lower [alpha/Fe] abundances indicate longer star formation histories pointing towards late accretion of the halo. This is consistent with independent evidence for on-going accretion, and suggests a connection to the observed size evolution of elliptical galaxies with redshift.Comment: 8 pages. Invited review to appear in the proceedings of "Galaxies and their Masks" eds. Block, D.L., Freeman, K.C. & Puerari, I., 2010, Springer (New York

Metal enrichment processes

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, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Evolución de sistemas de galaxias en el modelo CDM

Se realizaron simulaciones numéricas de N-cuerpos para estudiar la evolución de sistemas de galaxias en el contexto teórico del modelo CDM (Cold Dark Matter) con la normalización impuesta por la reciente determinación de las fluctuaciones en la temperatura de la radiación de fondo. Se implementaron modelos de formación de galaxias suponiendo un enfriamiento instantáneo del gas en regiones cuyo contraste de densidad local es alto. Los modelos analizados incluyen los efectos de fusión de galaxias, la acreción de gas y la inyección de energía al medio intergaláctico debido a vientos de supernovas. Los resultados obtenidos permiten dar cuenta de la relación observacional Tully-Fisher para galaxias espirales y del extremo débil de la función de luminosidad; como así también de la aparente disminución en la eficiencia de formación de galaxias en sistemas ricos. Los modelos no sustentan la existencia de efectos sistemáticos entre la dispersión de velocidades peculiares de las galaxias y la materia oscura indicando una gran dificultad del modelo CDM para reproducir las observaciones.Asociación Argentina de Astronomí

Chemical evolution of the galactic disk: evidence of an abundance gradient perpendicular to the galactic plane

Using a revised DDO abundance scale for the galactic open cluster system, the existence and size of the radial and axial abundance gradients, as well as the existence of a global age-metallicity relation in the galactic disk are investigated.Asociación Argentina de Astronomí