Merger-Induced Metallicity Dilution in Cosmological Galaxy Formation Simulations

Observational studies have revealed that galaxy pairs tend to have lower gas-phase metallicity than isolated galaxies. This metallicity deficiency can be caused by inflows of low-metallicity gas due to the tidal forces and gravitational torques associated with galaxy mergers, diluting the metal content of the central region. In this work we demonstrate that such metallicity dilution occurs in state-of-the-art cosmological simulations of galaxy formation. We find that the dilution is typically 0.1 dex for major mergers, and is noticeable at projected separations smaller than $40$ kpc. For minor mergers the metallicity dilution is still present, even though the amplitude is significantly smaller. Consistent with previous analysis of observed galaxies we find that mergers are outliers from the \emph{fundamental metallicity relation}, with deviations being larger than expected for a Gaussian distribution of residuals. Our large sample of mergers within full cosmological simulations also makes it possible to estimate how the star formation rate enhancement and gas consumption timescale behave as a function of the merger mass ratio. We confirm that strong starbursts are likely to occur in major mergers, but they can also arise in minor mergers if more than two galaxies are participating in the interaction, a scenario that has largely been ignored in previous work based on idealised isolated merger simulations.Comment: Submitted to MNRA

Spin evolution and feedback of supermassive black holes in cosmological simulations

It is well established that the properties of supermassive black holes and their host galaxies are correlated through scaling relations. While hydrodynamical cosmological simulations have begun to account for the co-evolution of BHs and galaxies, they typically have neglected the BH spin, even though it may play an important role in modulating the growth and feedback of BHs. Here we introduce a new sub-grid model for the BH spin evolution in the moving-mesh code {\small AREPO} in order to improve the physical faithfulness of the BH modelling in galaxy formation simulations. We account for several different channels of spin evolution, in particular gas accretion through a Shakura-Sunyaev $\alpha$-disc, chaotic accretion, and BH mergers. For BH feedback, we extend the IllustrisTNG model, which considers two different BH feedback modes, a thermal quasar mode for high accretion states and a kinetic mode for low Eddington ratios, with a self-consistent accounting of spin-dependent radiative efficiencies and thus feedback strength. We find that BHs with mass $M_{\rm{bh}}\lesssim 10^{8}\, {\rm M}_\odot$ reach high spin values as they typically evolve in the coherent gas accretion regime. On the other hand, BHs with mass $M_{\rm{bh}}\gtrsim 10^{8}\, {\rm M}_\odot$ have lower spins as BH mergers become more frequent, and their accretion discs fragment due to self-gravity, inducing chaotic accretion. We also explore the hypothesis that the transition between the quasar and kinetic feedback modes is mediated by the accretion mode of the BH disc itself, i.e.~the kinetic feedback mode is activated when the disc enters the self-gravity regime. We find excellent agreement between the galaxy and BH populations for this approach and the fiducial TNG model with no spin evolution. Furthermore, our new approach alleviates a tension in the galaxy morphology -- colour relation of the original TNG model.Comment: 22 pages, 13 figure, Submitted to MNRA

The kinematics of the Local Group in a cosmological context

Recent observations constrained the tangential velocity of M31 with respect to the Milky Way (MW) to be v_tan<34.4 km/s and the radial velocity to be in the range v_rad=-109+/- 4.4 km/s (van der Marel et al. 2012). In this study we use a large volume high resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the LCDM. The comparison of the ensembles of simulated pairs with the observed LG at the 1-sigma level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (e_tot), angular momentum (l_orb) and the dimensionless spin parameter, lambda. Our main results are: (i) the preferred radial and tangential velocities for pairs in LCDM are v_rad=-80+/-20 km/s, v_tan=50+/-10 km/s, (ii) pairs around that region are 3 to 13 times more common than pairs within the observational values, (iii) 15%to 24% of LG-like pairs in LCDM have energy and angular momentum consistent with observations while (iv) 9% to 13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e. e_tot, r_orb and lambda, do not challenge the standard LCDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the LCDM model to reproduce the observed LG.Comment: 6 pages, 2 figures, 3 tables, accepted for publication in ApJ Letters. For full data and source code (IPython notebook) to reproduce the results, see: https://github.com/forero/LG_Kinematic

Modelling supermassive black hole spins and the metallicity evolution of merging galaxies in a cosmological context

Galaxy mergers are a key process in the current paradigm of hierarchical galaxy formation. They are responsible for many galaxy transformations. For instance, they can drive changes in galaxy morphology and colour, boost the star formation activity and trigger strong inflows of pristine gas that dilute the central gas metallicity and feed the central supermassive black hole. To which extent and how galaxy mergers affect some of the galaxy properties are still open questions. In the first part of this thesis, we use simulations and observations to study the processes of merger-induced gas metallicity dilution and star formation enhancement. We find that merging and post-merger galaxies constitute a prominent outlier population in the fundamental metallicity relation, a relation that links the galaxy stellar mass with the star formation rate and the gas metallicity. In the second part of this thesis, we present a sub-grid model of supermassive black hole spin evolution in cosmological simulations of galaxy formation. We find that the accretion discs of low-mass black holes accrete mass in a coherent fashion, resulting in high spin values. On the other hand, high-mass black holes have lower spins because gas accretion is either chaotic or completely suppressed, in which case black hole binary coalescence resulting from galaxy mergers is the only relevant evolution channel. Finally, we test a hypothesis in which the black hole energy feedback transitions from a thermal mode to a kinetic mode at the onset of self-gravity fragmentation in the accretion disc, and is thus coupled to the spin evolution of the black hole. We find that our conjecture reproduces the galaxy colour bimodality and the colour-morphology relation

Calibracion y validacion del modelo hec – hms, en la cuenca de Huechun, Region Metropolitana

250 p.En la presente memoria, se probaron las capacidades del programa de simulación HEC- HMS, desarrollado por el U.S. Army Corps of Engineers, con el fin de generar hidrogramas de crecida y caudales punta, para la cuenca de Huechún, ubicada en la región Metropolitana de Chile, cuenca que carece de información fluviométrica. Para llevar a cabo esta simulación, se utilizó como plataforma de calibración y validación la cuenca de Colina, ubicada en esta misma región, la cual contaba con la ventaja de tener registros reales de caudales, medidos a través de su estación de río Colina en Peldehue. En líneas generales, ambas cuencas presentan precipitaciones de bajas intensidades en el periodo de estudio (1995 a 2007), estructuras de suelos con un alto nivel de permeabilidad y coberturas vegetacionales con un bajo desarrollo herbáceo y un bajo porcentaje de cobertura. Si bien se utilizaron como entradas del programa, el hidrograma unitario sintético de Snyder y el método del número de curva, para la generación de escorrentía y la transformación de ésta a los hidrogramas de crecida, la calibración de éste no pudo lograrse de forma óptima para el hidrograma de crecidas totales. En cambio, fue posible ajustar los inputs para que se generaran caudales punta bastante cercanos a los reales, lo cual permitió delinear los pasos a seguir para estimar valores por medio del HEC-HMS hacia la cuenca de Huechún. Como resultado final, es recomendable como una primera aproximación, el uso del programa HEC-HMS, para la generación de valores de caudales punta, en la cuenca de Huechún, aunque no es recomendable su uso para simular hidrogramas de crecida. Finalmente, en la cuenca de Huechún y para precipitaciones de montos superiores en un 100 % a las máximas registradas, en el periodo 1995 – 2007, sería posible encontrar caudales punta de hasta 24,7 m3/s

Relación entre el sentido de vida e ideación suicida en varones que consumen sustancias psicoactivas

El suicidio se muestra como una problemática en aumento a nivel mundial. Por ello, diversas prácticas en psicología intentan intervenir en esta problemática a través del descubrimiento de un sentido de vida. El objetivo de esta investigación consistió en identificar qué relación existe entre el sentido de vida y la ideación suicida en adultos varones que consumen sustancias psicoactivas. La muestra estuvo compuesta por 151 adultos varones entre los 18 y 62 años (M=23, DE=9.7) que consumen sustancias psicoactivas y pertenecen a dos centros de rehabilitación de Lima-Perú. Asimismo, se aplicaron dos instrumentos: el Test de sentido de vida (PIL) de Crumbaugh y Maholick y la Escala de ideación suicida (SSI) de Beck, de los cuales se adaptaron y describieron las propiedades psicométricas para dicha muestra. Los resultados evidencian que entre el sentido de vida y la ideación suicida existe una correlación negativa estadísticamente significativa (rho=-.425) con un tamaño del efecto medio (Ferguson, 2009). Además, los resultados del análisis factorial exploratorio indican una estructura interna unidimensional para ambas pruebas con una varianza única explicada de 40.7% para el SSI y 41.01% para el PIL; se hallaron coeficientes de consistencia interna significativos para el PIL (¿=.87) y el SSI (¿ = .84) y; en base a la información recolectada, se realizaron baremos generales para el análisis y la interpretación de las puntuaciones derivadas de muestras similares.Suicide appears to be a growing problem worldwide. For this reason, various practices in psychology try to intervene in this problem through the discovery of a meaning of life. The objective of this research was to identify the relationship between the meaning of life and suicidal ideation in male adults who use psychoactive substances. The sample consisted of 151 male adults between 18 and 62 years old (M = 23, SD = 9.7) who consume psychoactive substances and belong to two rehabilitation centers in Lima-Peru. Likewise, two instruments were applied: the Crumbaugh and Maholick Meaning of Life Test (PIL) and the Beck Scale of Suicidal Ideation (SSI), of which the psychometric properties were adapted and described for said sample. The results show that between the sense of life and suicidal ideation there is a statistically significant negative correlation (rho = -. 425) with a medium effect size (Ferguson, 2009). Furthermore, the results of the exploratory factor analysis indicate a one-dimensional internal structure for both tests with a single explained variance of 40.7% for the SSI and 41.01% for the PIL; significant internal consistency coefficients were found for the PIL (¿ = .87) and the SSI (¿ = .84) and; based on the information collected, general scales were made for the analysis and interpretation of the scores derived from similar samples

Estudio del comportamiento de inclusiones esféricas en un cilindro bajo traccion

In the present paper the behaviour of a hyperelastic body is studied, considering the presence of one, two and more spherical inclusions, under the effect of an external tension load. The inclusions are modeled as nonlinear elastic bodies that undergo small strains. For the material constitutive relation, a relatively new type of model is used, wherein the strains (linearized strain) are assumed to be nonlinear functions of the stresses. In particular, it is used a function such that the strains are always small, independently of the magnitude of the external loads. In order to simplify the problem, the hyperelastic medium and the inclusions are modelled as axial-symmetric bodies. The finite element method is used to obtain results for these boundary value problems. The objective of using these new models for elastic bodies in the case of the inclusions is to study the behaviour of such bodies in the case of concentration of stresses, which happens near the interface with the surrounding matrix. From the results presented in this paper, it is possible to observe that despite the relatively large magnitude for the stresses, the strains for the inclusions remain small, which would be closer to the actual behaviour of real inclusions made of brittle materials, which cannot show large strains.En el presente art\'iculo se estudia el comportamiento de un s\'olido hiper-el\'astico con una, dos y m\'as inclusiones esf\'ericas, bajo el efecto de una carga externa de tracci\'on. Las inclusiones se modelan como s\'olidos el\'asticos con comportamiento no-lineal y que presentan peque\~nas deformaciones, usando un nuevo modelo propuesto recientemente en la literatura, en donde las deformaciones (caso infinitesimal) se expresan como funciones no-lineales de las tensiones. En particular, se consideran expresiones para dichas funciones que aseguran que las deformaciones est\'an limitadas en cuanto a su magnitud independientemente de la magnitud de las cargas externas. Como una forma de simplificar el problema, el medio hiper-el\'astico y las inclusiones se modelan como s\'olidos axil-sim\'etricos. El m\'etodo de elementos finitos es usado para obtener resultados para estos problemas de valor de frontera. El objetivo del uso de los nuevos modelos para cuerpos elásticos para el caso de las inclusiones, es estudiar el comportamiento de dichos cuerpos en el caso de concentración de tensiones, lo cual ocurre cerca de la zona de interface con la matriz. De los resultados mostrados en este trabajo, es posible apreciar que a pesar de los valores relativamente altos para las tensiones, las deformaciones se mantienen pequeñas, lo cual sería mucho más cercano al comportamiento esperado en la realidad, cuando se trabaja con inclusiones hechas de un material frágil, el cual no puede mostrar grandes deformaciones