104 research outputs found

    The clustering of simulated quasars

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    We analyze the clustering properties of quasars simulated using a semianalytic model built on the Millennium Simulation, with the goal of testing scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers. When we select quasars with luminosities in the range accessible by current observations, we find that predicted values for the redshift evolution of the quasar bias agree rather well with the available data and the clustering strength depends only weakly on luminosity. This is independent of the lightcurve model assumed, since bright quasars are black holes accreting close to the Eddington limit. We also used the large catalogues of haloes available for the Millennium Simulation to test whether recently merged haloes exhibit a stronger large-scale clustering than the typical haloes of the same mass. This effect might help to explain the very high clustering strength observed for z~4 quasars. However, we do not detect any significant excess bias for the clustering of merger remnants, suggesting that objects of merger-driven nature do not cluster significantly differently than other objects of the same characteristic mass.Comment: 4 pages, 2 figures. To appear in the proceedings of "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", Eds. Sebastian Heinz, Eric Wilcots (AIP conference series

    The Role of Galaxy Mergers in the Evolution of Supermassive Black Holes

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    The high-redshift formation and evolution of Super-Massive Black Holes through semi-analytic models and photometric data

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    La formaci贸n y evoluci贸n de los Agujeros Negros Supermasivos (SMBHs) en el Universo temprano (z>6) representa una de las cuestiones abiertas m谩s enigm谩ticas de la Astrof铆sica moderna. De hecho, una creciente cantidad de evidencias observacionales apunta a la existencia de BHs de mil millones de masas solares a tan s贸lo 1Gyr del BigBang, impulsando cu谩sares extremadamente luminosos (QSOs). A pesar de los intensos esfuerzos te贸ricos de la 煤ltima d茅cada, los modelos actuales siguen teniendo dificultades para encajar la formaci贸n de estos objetos extremos en un tiempo cosmol贸gico tan corto. Adem谩s, a煤n no est谩 claro c贸mo se relacionan estos SMBHs de alto z con la poblaci贸n m谩s com煤n de SMBHs de desplazamiento al rojo inferior, que se cree que est谩 alojada de forma ubicua en los n煤cleos de las galaxias masivas. Explicar la formaci贸n y el crecimiento de una poblaci贸n global de SMBHs en su contexto cosmol贸gico presenta dificultades te贸ricas extremas que surgen de la necesidad de orquestar la f铆sica a peque帽a escala del enfriamiento del gas, la formaci贸n de estrellas y su retroalimentaci贸n radiativa y qu铆mica sobre el gas primordial, con la formaci贸n y evoluci贸n de la estructura a gran escala. Desde el punto de vista num茅rico, la formaci贸n de los SMBHs se estudia generalmente mediante simulaciones de alta resoluci贸n a peque帽a escala que pueden captar eficazmente la f铆sica a peque帽a escala implicada en este proceso. Sin embargo, la aplicaci贸n de estos resultados a cajas simuladas amplias y cosmol贸gicas es computacionalmente prohibitiva, por lo que la generalizaci贸n de estos resultados a escalas cosmol贸gicas es a煤n incierta. Desde el punto de vista de la observaci贸n, los experimentos actuales y futuros est谩n proporcionando mejores restricciones sobre la evoluci贸n cosmol贸gica de la poblaci贸n de SMBHs a lo largo de la historia c贸smica. En particular, los estudios espectrosc贸picos extensos y los estudios fotom茅tricos de banda estrecha de 谩rea amplia ofrecen una visi贸n complementaria de la poblaci贸n de n煤cleos gal谩cticos activos luminosos (AGN) y QSO, lo que permite restringir los modelos te贸ricos para la formaci贸n y el crecimiento de los SMBHs. Esta tesis presenta un enfoque novedoso que aborda este complejo fen贸meno mediante una combinaci贸n de m茅todos num茅ricos y t茅cnicas observacionales. M谩s detalladamente, incrustamos un modelo completo para la formaci贸n y el crecimiento de los SMBHs en el modelo semi-anal铆tico (SAM) L-Galaxies. A continuaci贸n, aplicamos nuestras prescripciones a los 谩rboles de fusi贸n de la simulaci贸n N-Body Millennium-II, que ofrece un compromiso 贸ptimo entre la resoluci贸n de masa y el volumen simulado. Esto permite estudiar la ocurrencia de la formaci贸n de SMBHs a trav茅s de todos los procesos f铆sicos actualmente previstos, as铆 como seguir de forma autoconsistente la evoluci贸n de los SMBHs dentro de su contexto cosmol贸gico. Por lo tanto, esto representa uno de los primeros intentos de modelar de forma autoconsistente la evoluci贸n de una poblaci贸n cosmol贸gica de SMBHs, emergiendo s贸lo de procesos de formaci贸n de alto z. Complementamos este enfoque te贸rico con un estudio observacional de la funci贸n de luminosidad Lyman-alfa (LF) de los AGN/QSOs a 2 6) que conducen a la formaci贸n de SMBHs pueden explicar activamente tanto la formaci贸n de objetos extremadamente masivos y QSOs despu茅s de 1 Gyr desde el BigBang, como la acumulaci贸n cosmol贸gica de la poblaci贸n global de SMBHs observada a desplazamientos al rojo m谩s moderados (2 <br /

    Black Hole Starvation and Bulge Evolution in a Milky Way-like Galaxy

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    We present a new zoom-in hydrodynamical simulation, "Erisbh", which follows the cosmological evolution and feedback effects of a supermassive black hole at the center of a Milky Way-type galaxy. ErisBH shares the same initial conditions, resolution, recipes of gas cooling, star formation and feedback, as the close Milky Way-analog "Eris", but it also includes prescriptions for the formation, growth and feedback of supermassive black holes. We find that the galaxy's central black hole grows mainly through mergers with other black holes coming from infalling satellite galaxies. The growth by gas accretion is minimal because very little gas reaches the sub-kiloparsec scales. The final black hole is, at z=0, about 2.6 million solar masses and it sits closely to the position of SgrA* on the MBH-MBulge and MBH-sigma planes, in a location consistent with what observed for pseudobulges. Given the limited growth due to gas accretion, we argue that the mass of the central black hole should be above 10^5 solar masses already at z~8. The effect of AGN feedback on the host galaxy is limited to the very central few hundreds of parsecs. Despite being weak, AGN feedback seems to be responsible for the limited growth of the central bulge with respect to the original Eris, which results in a significantly flatter rotation curve in the inner few kiloparsecs. Moreover, the disk of ErisBH is more prone to instabilities, as its bulge is smaller and its disk larger then Eris. As a result, the disk of ErisBH undergoes a stronger dynamical evolution relative to Eris and around z=0.3 a weak bar grows into a strong bar of a few disk scale lengths in size. The bar triggers a burst of star formation in the inner few hundred parsecs, provides a modest amount of new fuel to the central black hole, and causes the bulge of ErisBH to have, by z=0, a box/peanut morphology.(Abridged)Comment: 16 pages, 16 figures. Submitted to MNRA

    Bar-driven evolution and quenching of spiral galaxies in cosmological simulations

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    We analyse the output of the hi-res cosmological zoom-in simulation ErisBH to study self-consistently the formation of a strong stellar bar in a Milky Way-type galaxy and its effect on the galactic structure, on the central gas distribution and on star formation. The simulation includes radiative cooling, star formation, SN feedback and a central massive black hole which is undergoing gas accretion and is heating the surroundings via thermal AGN feedback. A large central region in the ErisBH disk becomes bar-unstable after z~1.4, but a clear bar-like structure starts to grow significantly only after z~0.4, possibly triggered by the interaction with a massive satellite. At z~0.1 the bar reaches its maximum radial extent of l~2.2 kpc. As the bar grows, it becomes prone to buckling instability, which we quantify based on the anisotropy of the stellar velocity dispersion. The actual buckling event is observable at z~0.1, resulting in the formation of a boxy-peanut bulge clearly discernible in the edge-on view of the galaxy at z=0. The bar in ErisBH does not dissolve during the formation of the bulge but remains strongly non-axisymmetric down to the resolution limit of ~100 pc at z=0. During its early growth, the bar exerts a strong torque on the gas within its extent and drives gas inflows that enhance the nuclear star formation on sub-kpc scales. Later on the infalling gas is nearly all consumed into stars and, to a lesser extent, accreted onto the central black hole, leaving behind a gas-depleted region within the central ~2 kpc. Observations would more likely identify a prominent, large-scale bar at the stage when the galactic central region has already been quenched. Bar-driven quenching may play an important role in disk-dominated galaxies at all redshift. [Abridged]Comment: 13 pages, 12 figures, MNRAS submitte

    Sustainable Waste Management Criteria for Local Urban Plans

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    The paper illustrates a new approach to waste management aiming at developing strategies and actions to be integrated into municipal planning tools. The local structure plan has been recognized as the planning tool in which to integrate sustainability objectives in the field of waste management. The door-to-door waste collection has been selected as the best strategy for guaranteeing high standards of waste separate collection in the new developments and restoration areas in the Bologna municipality. Following, criteria for dimensioning the space to be reserved for waste collection, both at the apartment and at the block scale and at urban scale have been proposed to be acknowledged into the local building regulations. The proposed approach has been verified through the application to a local development plan in the Bologna municipality and its feasibility has been tested both under the technical and economic point of view

    Galactic Bulges, spinning black holes and star forming galaxies in their cosmological context: insights from a semi-analytical perspective

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    Durante las 煤ltimas d茅cadas, los astrof铆sicos han desarrollado una teor铆a sobre c贸mo se forman y evolucionan las galaxias. A pesar de ser exitosa en muchos aspectos, todav铆a tiene ciertas limitaciones que trabajos te贸ricos y observacionales est谩n tratando de resolver. En esta tesis, contribuimos con estos trabajos te贸ricos abordando tres temas diferentes: bulbos gal谩cticos, agujeros negros supermasivos y el desarrollo de cat谩logos simulados para la nueva generaci贸n de cartografiados de banda estrecha. Hemos abordado todos estos temas utilizando el modelo semianal铆tico L-Galaxies . A grandes rasgos, los modelos semianal铆ticos consisten en seguir la evoluci贸n de la componente bari贸nica del Universo utilizando aproximaciones anal铆ticas aplicadas a 鈥溍boles鈥 de fusiones de materia oscura. L-Galaxies es uno de los modelos m谩s avanzados de la literatura, cuya capacidad para predecir las propiedades correctas de las galaxias en diferentes tiempos cosmol贸gicos ha sido probada durante la 煤ltima d茅cada en muchos trabajos. Una de las principales ventajas de L-Galaxies es la capacidad de se ejecutado en los 谩rboles de fusiones de materia oscura extra铆dos de las simulaciones Millennium cuyas diferencias en tama帽os de caja y resoluci贸n en masa de materia oscura ofrecen la posibilidad de explorar los procesos f铆sicos experimentados por la las galaxias en una amplia variedad de escalas y entornos. En la primera parte de la tesis, abordamos la formaci贸n de bulbos gal谩cticos con especial 茅nfasis en la poblaci贸n de pseudobulbos, cuya evoluci贸n en un universo jer谩rquico no ha sido del todo explorada. Concretamente, estudiamos su proceso de formaci贸n y caracterizamos las propiedades de sus galaxias anfitrionas a diferentes tiempos cosmol贸gicos. Dentro del marco que nos proporciona L-Galaxies , las galaxias son capaces de desarrollar un bulbo a trav茅s de fusiones con otras galaxias e inestabilidades de disco. Suponiendo que los pseudobulbos solo pueden formarse y crecer a trav茅s de una evoluci贸n secular, hemos modificado el tratamiento de las inestabilidades del disco de L-Galaxies asumiendo que solo los eventos de inestabilidad esencadenados por procesos seculares conducen a estructuras de barra duraderas que finalmente forman y desarrollan pseudobulbos. Hemos aplicado este escenario en L-Galaxies ejecutado sobre los 谩rboles de fusiones de Millennium y Millennium II. Los resultados del modelo est谩n en concordancia con las observaciones, mostrando que los pseudobulbos en el universo local son estructuras peque帽as ( 0:5 kpc) alojadas en galaxias similares a la V铆a L谩ctea. Estos resultados son alentadores y respaldan nuestra principal suposici贸n subyacente de que la estructura de pseudobulbo se forma principalmente a trav茅s de una evoluci贸n secular. Hemos ampliado nuestro an谩lisis de pseudobulbos estudiando el comportamiento del criterio de inestabilidad de disco utilizada por L-Galaxies cuando es aplicada a una muestra de galaxia con y sin barra extra铆da de la simulaci贸n hidrodin谩mica cosmol贸gica TNG100, actualmente una de las simulaciones m谩s completas disponible. A pesar de encontrar una correlaci贸n entre las predicciones del criterio anal铆tico y el (no) ensamblaje real de las galaxias con (no) barra, hemos detectado casos en los que el criterio anal铆tico falla, ya sea afirmando estabilidad del disco para galaxias barradas o inestabilidad del disco para las galaxias sin barra. Por ello, hemos propuesto una condici贸n nueva adicional para ser combinada con el criterio de L-Galaxies . Esta combinaci贸n mejora la detectabilidad de barras y reduce la contaminaci贸n de falsas galaxias barradas. La segunda parte de la tesis explora el ensamblaje en masas y la evoluci贸n del esp铆n de los agujeros negros supermasivos a lo largo del tiempo cosmol贸gico. Para ello, hemos actualizado el modelo L-Galaxies , incluyendo nuevos procesos f铆sicos. Hemos asumido que el crecimiento de los agujeros negros se desencadena principalmente a trav茅s de la acumulaci贸n de gas fr铆o despu茅s de fusiones de galaxias o inestabilidades de disco. Este crecimiento tiene lugar a trav茅s de una etapa de acrecimiento r谩pido seguida de un una lenta. Durante estas fases, la evoluci贸n del esp铆n del agujero negro es calculada usando de las propiedades morfol贸gicas del bulbo en el que reside. Las predicciones del modelo muestran una buena compatibilidad con los resultados observacionales como la funci贸n de masa de los agujeros negros, la distribuci贸n de sus valores de esp铆n, la relaci贸n entre la masa del bulbo y la del agujero negro y las funciones de luminosidad. Una de las principales novedades de esta tesis ha sido utilizar el modelo explicado anteriormente para explorar la formaci贸n y evoluci贸n de la poblaci贸n de agujeros negros errantes, es decir, una poblaci贸n que se encuentra fuera de las galaxias en 贸rbitas cerradas dentro de los subhalos de materia oscura. Hemos descubierto que la formaci贸n de este tipo de agujeros negros errantes deja una huella en la co-evoluci贸n entre el agujero negro y la galaxia anfitriona, pudiendo ser detectada por los estudios de galaxias actuales y futuros.Finalmente, la tercera parte de la tesis aborda el desarrollo de cat谩logos simulados especialmente dise帽ados para la nueva generaci贸n de cartografiados fotom茅tricos de banda estrecha. Con este fin, hemos incluido la construcci贸n de un cono de luz dentro de L-Galaxies incorporando en la fotometr铆a de las galaxias simuladas el efecto de l铆neas de emisi贸n producidas en regiones de formaci贸n estelar. Esto 煤ltimo ha asegurado la capacidad de los cat谩logos para predecir correctamente la fotometr铆a de galaxias en filtros de banda estrecha. Para determinar el flujo exacto en estas l铆neas hemos utilizado un modelo de emisi贸n nebular y de atenuaci贸n por el polvo capaz de predecir el flujo emitido por 9 l铆neas diferentes: Ly, H , H , [OII], [OIII], [NeIII], [OI], [NII] y [SII]. La validaci贸n de nuestro cono de luz se ha realizado comparando con diversas observaciones el n煤mero de galaxias detectado en diferentes filtros, la distribuci贸n angular de galaxias y las funciones de luminosidad de las l铆neas H , H , [OII] y[OIII]5007. Hemos utilizado todos estos procedimientos para generar cat谩logos especialmente dise帽ados para J-PLUS, un cartografiado fotom茅trico de galaxias que presenta una gran cantidad de filtros de banda estrecha. Al analizar estos cat谩logos hemos demostrado la capacidad del cartografiado para identificar correctamente la poblaci贸n de galaxias con l铆neas de emisi贸n a diferentes tiempos cosmol贸gicos.Como resumimos anteriormente, en esta tesis hemos abordado varios aspectos relacionados con la formaci贸n de galaxias, tratando de unir enfoques te贸ricos y observacionales. Sin duda alguna, el avance de los modelos te贸ricos combinado con los datos de experimentos futuros ayudar谩 a construir una imagen m谩s detallada de c贸mo se forman y evolucionan las estructuras en nuestro Universo.During the last decades, astrophysicists have developed a theory about how galaxies form and evolve within the Lambda-CDM cosmological framework. Despite being successful in many aspects, this general picutre has still some missing pieces that observational and theoretical works are trying to put all together. In this thesis, we try to answer to some open problems by addressing three different topics: galactic bulges, supermassive black holes and the development of mocks for the new generation of multi-narrow band surveys. We have tackled all these subjects by using the L-Galaxies semi-analytical model (SAM). Roughly, SAMs consist of dark matter merger trees populated with galaxies through analytical recipes. L-Galaxies is one of the state-of-the-art models whose capability to predict the correct galaxy properties at different redshifts has been proven during the last decade in many works. One of the main advantages of L-Galaxies is its flexibility to be run on the dark matter merger trees of the Millennium suite of simulations whose different box sizes and dark matter mass resolution offer the capability to explore different physical processes undergone by galaxies over a wide range of scales and environments. In the first part of the thesis, we address the cosmological build-up of galactic bulges with special focus on pseudobulges, whose cosmological evolution in a Lambda-CDM Universe has not been fully explored yet. In particular, we study their formation process and characterize the properties of their host galaxies at different redshifts. Within the L-Galaxies framework, galaxies are allowed to develop a bulge component via mergers and disk instabilities (DIs). Under the hypothesis that pseudobulges can only form and grow via secular evolution, we have modified the treatment of galaxy DIs. In detail, we assumed that only secular DI events lead to the development and growth of pseudobulges through the formation of long-lasting bar structures. We have applied this pseudobulge formation scenario to L-Galaxies, run on top of the Millennium and Millennium II dark matter merger trees. The outcomes of the model are in agreement with observations, showing that z=0 pseudobulges are small structures ~0.5 [kpc] hosted in main-sequence Milky Way-type galaxies. These results give support to our main underlying assumption that pseudobulge structure mainly form via secular evolution. We have extended our analysis of pseudobulge structures studying the performance of the DI criterion used by L-Galaxies when it is applied on a barred and unbarred galaxy sample of the cosmological hydrodynamical simulation TNG100. Despite finding a correlation between the analytical criteria predictions and the actual bar assembly (non-assembly) shown in the barred (unbarred) galaxies, we have detected cases where the analytical criterion fails, either claiming disk stability for barred galaxies or disk instability for the stable unbarred disks. We have proposed a new extra condition whose combination with the L-Galaxies criterion improves the detectability of bar structures and reduces both the contamination of fake barred galaxies and the number of undetected bar formation events. The second part of the thesis explores the mass assembly and spin evolution of supermassive black holes (BHs) across cosmic time. For this objective, we have updated L-Galaxies with new physical prescriptions. We have assumed that BH-mass assembly is mainly triggered by gas accretion after galaxy mergers or disk instabilities, and it takes place through a stage of rapid growth followed by a regime of slow accretion rates. During these phases, the BH spin evolution is followed by linking it with the morphological properties of the hosting bulge. The model predictions display a good consistency with some local observables, such as the black hole mass function, spin values distribution, BH-bulge mass relation and quasar luminosity functions. One of the main novelties of this thesis has been to use the BH model previously explained for exploring the formation and evolution of the wandering black hole population, i.e the population of BH outside of galaxies in bound orbits within the dark matter subhalos. We have found that the formation of these type of wandering black holes leave an imprint in the co-evolution between the black hole and the host galaxy which can be detected by current and future galaxy surveys. Finally, the third part of the thesis tackles the construction of mocks specially designed for the new generation of narrow-bands surveys. For this, we have inserted the lightcone assembly inside L-Galaxies, including in the photometry of the simulated galaxies the effect of emission lines produced in starforming regions. The latter has ensured the mock capability to correctly predict the galaxy photometry in narrow band filters. To determine the exact flux of emission lines we have used a model for the nebular emission in star-forming regions, coupled with a dust attenuation model, able to predict the flux emitted in 9 different lines. The validation of our lightcone has been done by comparing galaxy number counts, angular clustering, and Halpha, Hbeta, OII and OIII luminosity functions to a compilation of observations. We have applied all these procedures to generate catalogues tailored for J-PLUS, a large optical galaxy survey featuring a large number of narrow band filters. By analysing the J-PLUS mock catalogues, we have proved the ability of the survey to correctly identify a population of emission-line galaxies at various redshifts. As we summarize above, in this thesis we have tackled several aspects related to the details of galaxy formation, trying to bridge theoretical and observational approaches. The advance of theoretical models combined with the data from future experiments will certainly help to complete a detailed picture of how structures in our Universe form and evolve.<br /
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