Interacción de galaxias

Se describe un modelo en la aproximación restringida, para computar numéricamente la dinámica de un sistema galáctico binario interactuante, con distintas condiciones iniciales. Se discuten y comentan algunos resultados preliminares.Asociación Argentina de Astronomí

Galaxy morphology in dissipative models

Using numerical simulations in the context of a simple dissipative model (Abadi et al. 1990) we study the final morphologies and dynamical properties of galaxies under different initial conditions. The proto-galaxies are embedded in dynamically relaxed potential wells of dark matter with different initial spin parameters λ and velocity dispersions σ in the dissipative component. We find that both λ and σ control the final morphology of the galaxies. The angular momentum might be acquired by tidal torques, and several sources may account for the velocity dispersion. For instance, under the assumption that supernovae explosions provide kinetic energy to the medium giving σ ∼ 8 - 10 km/sec (Mc Kee and Ostriker 1977) our models suggest that the border line spin parameter between early and late types morphologies would be approximately λ ∼ 0.04.Asociación Argentina de Astronomí

Colisiones de sistemas autogravitantes

Se encuentran actualmente en análisis los resultados de las simulaciones numéricas de colisiones de sistemas esféricos de partículas inmersos en un "halo" común, con diferentes condiciones iniciales. Estas experiencias pueden representar la dinámica global de colisiones de galaxias, con halos masivos extendidos, pues las acciones tidales son más eficientes para éstos que para la componente luminosa, y por lo tanto, el merging de la componente estelar tendría lugar dentro de un único "halo" relajado.Asociación Argentina de Astronomí

Evolución de sistemas anisotrópicos en la presencia de "halos" masivos

Se analizan los resultados de una serie de experimentos numéricos concernientes a la distancia de sistemas de partículas bajo la influencia de una distribución de materia que representa un halo masivo. El análisis de las configuraciones relajadas en diferentes experiencias, muestra que la anisotropía espacial no es fuertemente afectada por la presencia de "halos" masivos. Nuestros resultados extienden de esta manera, aquellos obtenidos por Aarseth y Binney (1978) en el sentido de que la relajación violenta no borra eficazmente las condiciones iniciales de sistemas autogravitantes.Asociación Argentina de Astronomí

Eventos astrofísicos y formación de estructura

Se están estudiando los procesos astrofísicos vinculados a los eventos de explosión de supernova. En particular se analiza la posibilidad que la energía liberada pueda modificar la dinámica local en un esquema jerárquico de formación de estructura como el modelo Coid Dark Matter. Además, se está trabajando en la elaboración de un programa de cómputos basado en el esquema particle - mesh y que permita un tratamiento adecuado de las interacciones partícula - partícula en escalas menores que la resolución del potencial de la red. Esto permitiría un cómputo mas preciso de estos modelos.Asociación Argentina de Astronomí

The chemical enrichment of the ICM from hydrodynamical simulations

The study of the metal enrichment of the intra-cluster and inter-galactic media (ICM and IGM) represents a direct means to reconstruct the past history of star formation, the role of feedback processes and the gas-dynamical processes which determine the evolution of the cosmic baryons. In this paper we review the approaches that have been followed so far to model the enrichment of the ICM in a cosmological context. While our presentation will be focused on the role played by hydrodynamical simulations, we will also discuss other approaches based on semi-analytical models of galaxy formation, also critically discussing pros and cons of the different methods. We will first review the concept of the model of chemical evolution to be implemented in any chemo-dynamical description. We will emphasise how the predictions of this model critically depend on the choice of the stellar initial mass function, on the stellar life-times and on the stellar yields. We will then overview the comparisons presented so far between X-ray observations of the ICM enrichment and model predictions. We will show how the most recent chemo-dynamical models are able to capture the basic features of the observed metal content of the ICM and its evolution. We will conclude by highlighting the open questions in this study and the direction of improvements for cosmological chemo-dynamical models of the next generation.Comment: 25 pages, 11 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 18; 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

Towards the high-accuracy determination of the 238U fission cross section at the threshold region at CERN - N-TOF

The 238U fission cross section is an international standard beyond 2 MeV where the fission plateau starts. However, due to its importance in fission reactors, this cross-section should be very accurately known also in the threshold region below 2 MeV. The 238U fission cross section has been measured relative to the 235U fission cross section at CERN - n-TOF with different detection systems. These datasets have been collected and suitably combined to increase the counting statistics in the threshold region from about 300 keV up to 3 MeV. The results are compared with other experimental data, evaluated libraries, and the IAEA standards

A Prospective Evaluation of Infant Cerebellar-Cerebral Functional Connectivity in Relation to Behavioral Development in Autism Spectrum Disorder

Background: Autism spectrum disorder (ASD) is a neurodevelopmental disorder diagnosed based on social impairment, restricted interests, and repetitive behaviors. Contemporary theories posit that cerebellar pathology contributes causally to ASD by disrupting error-based learning (EBL) during infancy. The present study represents the first test of this theory in a prospective infant sample, with potential implications for ASD detection. Methods: Data from the Infant Brain Imaging Study (n = 94, 68 male) were used to examine 6-month cerebellar functional connectivity magnetic resonance imaging in relation to later (12/24-month) ASD-associated behaviors and outcomes. Hypothesis-driven univariate analyses and machine learning–based predictive tests examined cerebellar–frontoparietal network (FPN; subserves error signaling in support of EBL) and cerebellar–default mode network (DMN; broadly implicated in ASD) connections. Cerebellar-FPN functional connectivity was used as a proxy for EBL, and cerebellar-DMN functional connectivity provided a comparative foil. Data-driven functional connectivity magnetic resonance imaging enrichment examined brain-wide behavioral associations, with post hoc tests of cerebellar connections. Results: Cerebellar-FPN and cerebellar-DMN connections did not demonstrate associations with ASD. Functional connectivity magnetic resonance imaging enrichment identified 6-month correlates of later ASD-associated behaviors in networks of a priori interest (FPN, DMN), as well as in cingulo-opercular (also implicated in error signaling) and medial visual networks. Post hoc tests did not suggest a role for cerebellar connections. Conclusions: We failed to identify cerebellar functional connectivity–based contributions to ASD. However, we observed prospective correlates of ASD-associated behaviors in networks that support EBL. Future studies may replicate and extend network-level positive results, and tests of the cerebellum may investigate brain-behavior associations at different developmental stages and/or using different neuroimaging modalities

Transferencia de momentos angulares entre sistemas auto-gravitantes

A partir de experiencias numéricas se estudia la adquisición de momento angular intrínseco a expensas del momento orbital en un par de sistemas débilmente interactuantes.Asociación Argentina de Astronomí

Colapso y relajación de sistemas de N cuerpos

Se discuten las propiedades cualitativas y cuantitativas del colapso, relajación y escapes en sistemas esferoidales auto-gravitantes de N partículas, basadas en varias experiencias numéricas.Asociación Argentina de Astronomí