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Study of the Chemical and Morphological Evolution of Molecular Clouds, Using Observations of High Density Gas Tracers

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Study of the Chemical and Morphological Evolution of Molecular Clouds, Using Observations of High Density Gas Tracers Programa de Doctorado en Física y Matemáticas Study of the chemical and morphological evolution of molecular clouds, using observations of high density gas tracers Dissertation presented by: Guillermo Manjarrez Esquivel dvisors: Dr! "osé Francisco Gómez %ivero Dr! &tziar de Gregorio Monsalvo Granada, ()*+ Agradecimientos Agradezco a mis directores de tesis, Jos´eFrancisco G´omez Rivero e Itziar de Gregorio Monsalvo por todo el apoyo que me proporcionaron para la realizaci´on de este trabajo. Mi agradecimiento tambi´en para Guillem, Mayra, Ana Karla y los compa˜neros que formaron parte del grupo de Radioastronom´ıa durante mi estancia en el Instituto de Astrof´ısica de Andaluc´ıa. De todos ellos aprend´ımucho. Igualmente agradezco al personal del IAA por todo el apoyo que recib´ıen el instituto. Tambi´en agradezco a los amigos y amigas que hicieron de mi estancia en Granada una gran experiencia de vida. Agradezco a mi familia, que me apoy´oen todo momento. i ii Summary Stars are formed in dense regions within molecular clouds. The different phenomena associated with the star formation processes may be characterized by studying its dust and gas content. The analysis of thermal emission of different molecular species is a powerful tool to characterize the physical, kinematical, and chemical properties of these regions. The abundance of some of these molecules changes as the clouds evolve. In this context, the so called “early-type molecules”, such as CCS, have higher abundance in the first stages of cloud evolution than in star forming regions, while the opposite trend is seen in late-type molecules, such as NH3 (Suzuki et al. 1992). Therefore, the abundance ratio [CCS]/[NH3] was proposed as an indicator of cloud evolution, with its value being higher for pre-stellar clouds and decreasing as star formation proceeds (Suzuki et al. 1992). However, in their study of the star-forming region B1-IRS, De Gregorio-Monsalvo et al. (2005) found some evidence that the production of CCS takes place not only at the earlier stages of the cloud evolution, but also at later stage, after the onset of star formation. This implied that the abundance ratio [CCS]/[NH3] may properly characterize the evolutionary stage of active star forming regions. In this thesis we present a follow-up of these studies, analyzing the emission of CCS and NH3 at small scales in a sample of molecular clouds at different stages of their evolution, from starless cores to active star forming regions. Our aim was to investigate if the spatial ′′ anticorrelation between CCS and NH3 previously observed in B1-IRS at small scales (≃ 5 ) is present in other clouds and over a range of evolutionary stages. We also aimed at studying a possible CCS enhancement due to the interaction between the ambient dense gas and molecular outflows. Our sample included some dense starless cores in TMC-1, the very young star forming region GF9-2, and the region surrounding the protostars L1448 IRS3 and L1448C. To carry out these studies, we observed the CCS and NH3 emission in these regions at high angular resolution using the Very Large Array (VLA) interferometer. In addition, we observed other molecular tracers like CO and water masers to trace energetic mass- loss processes associated with young stellar objects in the studied regions, as well as continuum emission tracing dust (at millimeter wavelengths) and ionized gas (at centimeter wavelengths). These included data taken with the Effelsberg radio telescope and archival data from the Atacama Large Millimeter/submillimeter Array. Our data provided us with detailed information of the morphology, kinematics and physical conditions surrounding young protostars. iii iv In the dark pre-stellar cloud TMC-1, our results showed that the cores B and D present a clear chemical differentiation. We found that the CCS-NH3 anticorrelation stands even at ′′ small scales (∼ 4 ) within each core. Core B showed intense NH3 emission with filamentary structure, and seems to be in a relatively advanced stage of cloud evolution. We also found that the spacing between cores (∼ 0.1 pc) is in agreement with the scale of fragmentation of collapsing cores in filaments derived from models. On the other hand, Core D presents CCS emission with a more clumpy structure, suggesting that this core is very young and less evolved than core B. In GF9-2 (a cloud that contains a very young class 0 protostar that does not power an extensive molecular outflow), we found a clear CCS-NH3 anticorrelation, with no evidence of CCS enhancement due to star-forming activity. We also identified a possible “blue spot” signature (as defined by May´en-Gij´on et al. 2014), suggesting the presence of infall and rotation. This is the first time this signature is found in a low mass star forming region. The protostar in GF9-2 is also the lowest luminosity young stellar object (YSO) for which a possible association with water maser emission has been reported, but our VLA observations could not confirm it. We then carried out observations of water masers in a sample of low luminosity YSOs and brown dwarfs, to find out the luminosity limit at which water maser emission can be produced. We did not detect any emission in our targets, which suggests that the correlation between water maser luminosities and bolometric luminosities does not hold at the lower end of the (sub)stellar mass spectrum. In the L1448 region (an active star forming region that contains multiple YSOs and outflows) we also observed spatial anticorrelation between CCS and NH3, around the YSO L1448C. The presence of relatively strong CCS cores close to the outflow trajectory suggests that the CCS abundance is enhanced by star-forming activity, like in B1-IRS. The velocity gradients of CCS and NH3 have opposite signs south of L1448C, illustrating the complementarity of both molecules, and that observing only one of them would provide a biased view of the physical processes in the region. Using ALMA data we found a dust jet traced by millimeter continuum emission. This is the first time that thermal dust emission is detected in a jet, and traced up to its origin from a circumstellar disk. Our results suggested that jets can be powered by disk winds launched from a wide range of radii, as proposed in D-wind models. In this source, we also detected a Keplerian disk with C18O observations, with a radius ≃ 450 au, which is larger than in other Class-0 protostars. In AFGL 437 (a high mass star forming region with a poorly collimated outflow), we suggest that the low-collimation CO outflow could be the superposition of individual outflows from different sources, rather than being the interaction of the wind from a single object with an anisotropic environment, as previously suggested. One of the main general results of the thesis is that the chemical evolution of molecular clouds (in particular, the abundance of CCS and NH3) is not only a time dependent process, but also depends on different physical conditions present in advanced stages of the formation of a star. Therefore, the abundance ratio CCS-NH3 may not be useful to study the stage of the evolution of active star forming regions with multiple YSOs and/or very energetic outflows, since their interactions with ambient gas may trigger CCS regeneration, v which may provide misleading conclusions if a linear evolutionary interpretation is applied. vi Resumen Las estrellas se forman en las regiones m´as densas de las nubes moleculares. Los diferentes fen´omenos asociados a los procesos de formaci´on estelar pueden caracterizarse estudiando su contenido de gas y polvo. El an´alisis de la emisi´on t´ermica de diferentes especies moleculares y sus transiciones son una poderosa herramienta para caracterizar las propiedades f´ısicas, cinem´aticas y qu´ımicas de esas regiones. La abundancia de algunas de estas mol´eculas cambia conforme las nubes evolucionan. En este contexto, las llamadas “mol´eculas tempranas”, como CCS, presentan una mayor abundancia en las primeras etapas de evoluci´on de las nubes que en regiones de formaci´on estelar, mientras que la tendencia opuesta se observa en las mol´eculas de tipo tard´ıo, como NH3 (Suzuki et al. 1992). As´ı, el cociente de abundancias [CCS]/[NH3] fue propuesto como un indicador de evoluci´on de las nubes, siendo mayor para nubes preestelares y este disminuye al ir avanzando la formaci´on estelar (Suzuki et al. 1992). Sin embargo, en su estudio de la regi´on B1-IRS, De Gregorio-Monsalvo et al. (2005) encontraron evidencia de que la producci´on de CCS tiene lugar no solo en las etapas tempranas de la evoluci´on de las nubes, sino tambi´en en etapas tard´ıas, despu´es de la formaci´on de la estrella. Esto tambi´en implic´o que el uso del cociente de abundancias [CCS]/[NH3] podr´ıa no ser ´util para caracterizar apropiadamente la etapa evolutiva de las regiones de formaci´on estelar activa. En esta tesis continuamos con estos estudios, analizando la emisi´on de CCS y NH3 a peque˜na escala en una muestra de nubes moleculares en diferentes etapas de evoluci´on, que van de n´ucleos densos sin estrella a regiones de formaci´on estelar activa. Nuestro objetivo es investigar si la anticorrelaci´on espacial entre CCS y NH3 previamente observada en B1-IRS est´apresente en otras nubes y sobre un intervalo de etapas evolutivas. Tambi´en estudiamos el posible enriquecimiento de CCS debido a la interacci´on entre el gas ambiente denso y flujos moleculares. La muestra contiene algunos n´ucleos densos de la nube TMC-1, la muy joven regi´on de formaci´on estelar GF9-2, y la regi´on alrededor de las protoestrellas L1448 IRS3 y L1448C.
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