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Chemical Evolution of the Large Magellanic Cloud) EVOLUCIÓN QUÍMICA DE LA NUBE GRANDE DE MAGALLANES. (CHEMICAL EVOLUTION OF THE LARGE MAGELLANIC CLOUD) Profesor Guía: Dr. Douglas Geisler Tesis para optar al grado académico de Doctor en Ciencias Físicas Autor RENEÉ CECILIA MATELUNA PÉREZ CONCEPCIÓN - CHILE NOVIEMBRE 2012 Director de Tesis : Dr. Douglas Geisler Departamento de Astronomia, Universidad de Concepción, Chile. Comisión Evaluadora : Dr. Giovanni Carraro. European Southern Observatory, Santiago, Chile. Dipartimento di Astronomia, Universitá di Padova, Padova, Italia. Dr. Sandro Villanova. Departamento de Astronomia, Universidad de Concepción, Chile. Dr. Tom Richtler. Departamento de Astronomia, Universidad de Concepción, Chile. Dedicado a Mi Padre Agradecimientos He llegado al final de un ciclo, y son muchas las personas que me han acompañado de alguna u otra forma en este proceso. Por esta razón, es que decidí hacer estos agradecimientos en un orden más o menos cronológico. Comenzaré por mis padres: Cecilia y René, ya que gracias a ellos estoy aquí. Mamá has sido un gran apoyo en este camino, te agradezco cada gesto de amor y cada sabio consejo que me has dado. Papá, aunque no estas físicamente presente para presenciar este momento, agradezco la oportunidad que me diste para ser fuerte y seguir adelante con mis sueños a pesar de las dificultades y se que estarías muy orgulloso de mi. Muchas gracias papá por el legado que me dejaste, mis hermanos: Alejandra, Gabriel, Mariela, José Luis y Alfredo, con ellos aprendo cada día de que en la diversidad esta la belleza y la armonía, muchas gracias, son un gran apoyo, los amo. A mis tios y primos: tia Quelita, tio Rene, Dany, Pauta y a mi comadre(Cecilia), gracias por entregarme su amor, sus consejos y esos momentos de celebración y risas. A los amig@s: Candy-Candy, Chany, Dany, Anis, Jessika, Nico, ustedes que creyeron en que este sueño se haría realidad mucho antes de que comenzara, me dieron su apoyo, su confianza y muchas risas compartidas hasta hoy, mil gracias. A la comunidad ’Physilandia’: Leo, Carlitos, Arturo G., Omar, Yaz, Marisol y Faio, les agradezco los grandes momentos vividos en la que fuera por un tiempo nuestra casa, el "Phys". Rodrigo F., gracias por la ayuda técnica y el apoyo durante el proceso final. A Roger, gracias por tus sabias palabras. A Nelson, quien fue un gran compañero durante parte de este camino, gracias por ser un apoyo y por la alegría que me entregaste en momentos importantes de mi vida. A Guille D. y Coté mis amiguitos ’PIA’...gracias por compartir este sueño. A mis nuevos ’compañeritos’, el equipo de divulgadores AstroUdec: Pamela, Paula, Gustavo, Matias y Roy, han sido un apoyo importante durante mi último año de este proceso, muchas gracias por aparecer en el momento preciso. Especialmente a Pamela, Gustavo y Paula gracias por la alegría y los momentos ñoños!!! Agradezco a mis referentes femeninos dentro de la astronomía: Stella, Karen, Amelia, Maja, Sonia y Barbara, las admiro mucho y son una fuente de motivación constante, gracias por el apoyo y los consejos. A mis compañeritos de la ESO: Mauricio, Mono, Florian, Joachim, Matias, Karla, Lucy, Daniela (compañera de oficina y amiga), muchas gracias por los almuerzos de sushi en ’patota’ y esos cafecitos de tarde conversados. A los postdocs que apoyaron mi trabajo de Tesis: Sandro y Karen, muchas gracias por el tiempo y la dedicación en resolver mis dudas. Christian, un gran apoyo en el primer ’run’ de observación en Las Campanas, muchas gracias. A mis tutores: Doug y Giovanni, muchas gracias por su paciencia, apoyo y visión. A Hugo Schwarz, el primero en depositar su confianza en mi ii y quien me guió al comienzo de este camino: aunque ya no estás para ver el resultado, muchas gracias por las enseñanzas, no olvidaré tus consejos. A quienes son parte de la Facultad y me apoyaron durante este proceso: Calu, muchas gracias por los necesarios ’breaks’ y los consejos. Jeanette, gracias por tu buena onda y por tus ricos ’coffees’. Paulina, gracias por el apoyo y el dinamismo y Marcelita, muchas gracias por tu paciencia y tu buena voluntad. Muchas gracias al comité evaluador por sus oportunos comentarios sobre esta Tesis. Agradezco a CONICYT, ESO y al proyecto BASAL por el financiamiento en la realización de esta tesis de doctorado. A todos aquellos que me han acompañado en algún momento y que no fueron nombrados, gracias por existir y haber sido parte de mi vida y de esta experiencia. Finalmente agradezco a la organización Condor Blanco: Suryavan Solar, Sol, LAma Norbu, Lama Dorje, Lexim de Gerand, Shirayam, Mankardo, Kin-Yasai, Lantui, Sekuyali, Manuvari, Samirati, Sayaru, Yamkaishi y a toda la tribu CB, gracias a todos por su apoyo en el mejor de los caminos que he conocido: el del autoconocimiento y la búsqueda de la realización. Tesis de Doctorado Resumen Una de las grandes preguntas en astronomía es cómo se formó nuestra Galaxia y otras galax- ias, siendo ésta la motivación principal para esta tesis. Los dos escenarios más aceptados para formación de Galaxias, en particular el halo, para el propósito de este trabajo, son ’El Modelo de Colapso Monolítico’ y ’El Modelo Jerárquico de Acreción’. El último, es una versión temprana, independiente de lo que ha sido generalizado y ampliamente expandido para formar el modelo de acreción jerárquico ΛCDM, el cual predice una estructura de formación jerárquica en todas las escalas físicas, convirtiendo a las galaxias esferoidales enanas (dSph) y enanas irregulares (dIrr), en muy buenas candidatas para ser ’building block’ de nuestra Galaxia. Tomando en cuenta este último escenario, además de la intrigrante población de cúmulos estelares y lo poco que se conoce sobre evolución química de nuestra galaxia vecina, la Nube Mayor de Magallanes (LMC), se decidió llevar a cabo un estudio de esta galaxia basado en tres objetivos claros. Primero, limitar químicamente el modelo jerárquico para formación de Galaxia determinando abundancias en SCs, en la LMC. Segundo, estudiar la evolución química de la LMC al sumar la mayor cantidad de puntos como sea posible a la relación edad-metalicidad (AMR), incluyendo tanto los cúmulos como las estrellas del campo, y estudiando tantos elementos como sea posible para investigar una gran variedad de vías nucleosintéticas, y tercero, para comprobar si la técnica de CaT presenta posibles fallas en la determinación de la metalicidad en la LMC. Para este propósito, se recolectó un gran conjunto de datos. Se realizó espectroscopía de alta resolución (FLAMES@VLT) y fotometría de Washington, usando un instrumento de campo amplio (MOSAIC@4mCTIO), para cúmulos estelares y estrellas del campo de la LMC. El rango espectral me permitió medir una variedad de elementos, incluyendo Fe, Mg, Ca, Ti, Si, Na, O, Ni, Cr, Sc, Mn, Co, Zn, Ba, La, Eu e Y. Se analizaron dos cúmulos estelares (Hodge11 y SL869) y 21 campos de la LMC. Del análisis de la espectroscopía de alta resolución (HRS), se obtuvo una metalicidad de [Fe/H]= −2.00 ± 0.04( σobs = 0.11 ± 0.03), para el cúmulo viejo Hodge 11(H11), en acuerdo con estudios anteriores. Y por primera vez para SL869, una metalicidad de [FeI/H]= −0.47 (σint = 0.04). Además, se estimó una edad de 1.45 Gyr, σ = 0.2Gyr, para SL869 usando un ajuste de isocronas. Uno de los resultados más importantes en este estudio es aquel que proviene del valor medio de [α/Fe] vs [Fe/H] (Fig. 3.7). Encontramos que H11 se encuentra en el rango de las dSph y bajo el valor observado en la Galaxia. Este resultado confirma estudios previos y abre la posibilidad a que galaxias como la LMC, que se asumieron como ’building blocks’ de nuestra galaxia, puedan de hecho no satisfacer los requerimientos químicos, incluso en la metalicidad baja representada iv por H11. En los elementos iron-peak, también se ven abundancias similares a los resultados de dSph, tales como baja Cr, Mn y Ni. Los resultados de este trabajo, respecto de la evolución química de la LMC, están bien descritos por un modelo de ’bursting’ propuesto por Pagel & Tautvaisiene (1998), con la excepción del campo más antiguo, donde los errores para la edad son considerablemente mayores. Estos resultados muestran un incremento muy suave en la metalicidad sobre el período de edad de ∼4-11 Gyr, estando en excelente acuerdo con el modelo de ’bursting’. SL869 también está en muy buen acuerdo con este modelo, e incluso cúmulos más jóvenes muestran inequívocamente un incremento en el enriquecimiento químico predicho por este modelo en los últimos Gyrs. A pesar de que nuestros datos ajustan bien con el modelo, es necesario analizar muchos más datos, especialmente a bajas metalicidades, con el fin de tener una idea más clara sobre la formación de la LMC y por tanto de nuestra propia galaxia. Tesis de Doctorado Abstract Understanding how our Galaxy and other galaxies formed is one of the big questions in As- tronomy and is the principal motivation for this thesis. The two most widely accepted scenarios for Galaxy formation, in particular the halo, for the purpose of this work, are ’The Monolithic Col- lapse Model’ and ’The Merger/Hierarchical Accretion Model’. The last is an early, independent version of what has now been generalized and greatly expanded to form the ΛCDM hierarchical accretion model, which predicts hierarchical structure formation on all physical scales, turning dwarf spheroidal (dSph) and dwarf irregular (dIrr) galaxies very good candidates to be building blocks of our Galaxy. Taking this last scenario into account, plus the intriguing star cluster population and what lit- tle is known of the chemical evolution of our galaxy neighbour, the Large Magellanic Cloud(LMC), it was decided to proceed with a study of this galaxy based on three clear aims.
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