The clustering of simulated quasars

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

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

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

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

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

La formación y evolución de los Agujeros Negros Supermasivos (SMBHs) en el Universo temprano (z>6) representa una de las cuestiones abiertas más enigmáticas de la Astrofísica moderna. De hecho, una creciente cantidad de evidencias observacionales apunta a la existencia de BHs de mil millones de masas solares a tan sólo 1Gyr del BigBang, impulsando cuásares extremadamente luminosos (QSOs). A pesar de los intensos esfuerzos teóricos de la última década, los modelos actuales siguen teniendo dificultades para encajar la formación de estos objetos extremos en un tiempo cosmológico tan corto. Además, aún no está claro cómo se relacionan estos SMBHs de alto z con la población más común de SMBHs de desplazamiento al rojo inferior, que se cree que está alojada de forma ubicua en los núcleos de las galaxias masivas. Explicar la formación y el crecimiento de una población global de SMBHs en su contexto cosmológico presenta dificultades teóricas extremas que surgen de la necesidad de orquestar la física a pequeña escala del enfriamiento del gas, la formación de estrellas y su retroalimentación radiativa y química sobre el gas primordial, con la formación y evolución de la estructura a gran escala. Desde el punto de vista numérico, la formación de los SMBHs se estudia generalmente mediante simulaciones de alta resolución a pequeña escala que pueden captar eficazmente la física a pequeña escala implicada en este proceso. Sin embargo, la aplicación de estos resultados a cajas simuladas amplias y cosmológicas es computacionalmente prohibitiva, por lo que la generalización de estos resultados a escalas cosmológicas es aún incierta. Desde el punto de vista de la observación, los experimentos actuales y futuros están proporcionando mejores restricciones sobre la evolución cosmológica de la población de SMBHs a lo largo de la historia cósmica. En particular, los estudios espectroscópicos extensos y los estudios fotométricos de banda estrecha de área amplia ofrecen una visión complementaria de la población de núcleos galácticos activos luminosos (AGN) y QSO, lo que permite restringir los modelos teóricos para la formación y el crecimiento de los SMBHs. Esta tesis presenta un enfoque novedoso que aborda este complejo fenómeno mediante una combinación de métodos numéricos y técnicas observacionales. Más detalladamente, incrustamos un modelo completo para la formación y el crecimiento de los SMBHs en el modelo semi-analítico (SAM) L-Galaxies. A continuación, aplicamos nuestras prescripciones a los árboles de fusión de la simulación N-Body Millennium-II, que ofrece un compromiso óptimo entre la resolución de masa y el volumen simulado. Esto permite estudiar la ocurrencia de la formación de SMBHs a través de todos los procesos físicos actualmente previstos, así como seguir de forma autoconsistente la evolución de los SMBHs dentro de su contexto cosmológico. Por lo tanto, esto representa uno de los primeros intentos de modelar de forma autoconsistente la evolución de una población cosmológica de SMBHs, emergiendo sólo de procesos de formación de alto z. Complementamos este enfoque teórico con un estudio observacional de la función de luminosidad Lyman-alfa (LF) de los AGN/QSOs a 2 6) que conducen a la formación de SMBHs pueden explicar activamente tanto la formación de objetos extremadamente masivos y QSOs después de 1 Gyr desde el BigBang, como la acumulación cosmológica de la población global de SMBHs observada a desplazamientos al rojo más moderados (2 <br /

On merger bias and the clustering of quasars

We use the large catalogues of haloes available for the Millennium Simulation to test whether recently merged haloes exhibit stronger large-scale clustering than other haloes of the same mass. This effect could help to understand the very strong clustering of quasars at high redshift. However, we find no statistically significant excess bias for recently merged haloes over the redshift range 2 < z < 5, with the most massive haloes showing an excess of at most ~5%. We also consider galaxies extracted from a semianalytic model built on the Millennium Simulation. At fixed stellar mass, we find an excess bias of ~ 20-30% for recently merged objects, decreasing with increasing stellar mass. The fact that recently-merged galaxies are found in systematically more massive haloes than other galaxies of the same stellar mass accounts for about half of this signal, and perhaps more for high-mass galaxies. The weak merger bias of massive systems suggests that objects of merger-driven nature, such as quasars, do not cluster significantly differently than other objects of the same characteristic mass. We discuss the implications of these results for the interpretation of clustering data with respect to quasar duty cycles, visibility times, and evolution in the black hole-host mass relation.Comment: 10 pages, 9 figures. Submitted to MNRAS. Comments welcom