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 /

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

Improving the formal verification of reachability policies in virtualized networks

Network Function Virtualization (NFV) and Software Defined Networking (SDN) are new emerging paradigms that changed the rules of networking, shifting the focus on dynamicity and programmability. In this new scenario, a very important and challenging task is to detect anomalies in the data plane, especially with the aid of suitable automated software tools. In particular, this operation must be performed within quite strict times, due to the high dynamism introduced by virtualization. In this paper, we propose a new network modeling approach that enhances the performance of formal verification of reachability policies, checked by solving a Satisfiability Modulo Theories (SMT) problem. This performance improvement is motivated by the definition of function models that do not work on single packets, but on packet classes. Nonetheless, the modeling approach is comprehensive not only of stateless functions, but also stateful functions such as NATs and firewalls. The implementation of the proposed approach achieves high scalability in complex networked systems consisting of several heterogeneous functions

An H{\alpha} Impression of Ly{\alpha} Galaxies at z≃6z\simeq6 with Deep JWST/NIRCam Imaging

We present a study of seven spectroscopically confirmed Ly{\alpha} emitting galaxies at redshift $z\simeq6$ using the James Webb Space Telescope (JWST) NIRCam images. These galaxies, with a wide range of Ly{\alpha} luminosities, were recently observed in a series of NIRCam broad- and medium-bands. We measure the continuum and H{\alpha} line properties of the galaxies using the combination of the NIRCam photometry and archival Hubble Space Telescope imaging data. We find that galaxies with bluer UV continuum slopes likely have higher escape fractions of Ly{\alpha} photons. We also find that galaxies with higher Ly{\alpha} line emission tend to produce ionizing photons more efficiently. The most Ly{\alpha}-luminous galaxy in the sample has a high ionizing photon production efficiency of log$_{10} \xi_{\rm ion, 0}$ (Hz erg$^{-1}$) > 26. Our results support that Ly{\alpha} galaxies may have served as an important contributor to the cosmic reionization. Blue and bright Ly{\alpha} galaxies are also excellent targets for JWST follow-up spectroscopic observations.Comment: 10 pages, 4 figures, 2 tables, submitted to ApJ

The miniJPAS & J-NEP surveys: Identification and characterization of the Lyα\alpha Emitter population and the Lyα\alpha Luminosity Function

We present the Lyman-$a$ (Lya) Luminosity Function (LF) at $2.05<z<3.75$, estimated from a sample of 67 Lya-emitter (LAE) candidates in the J-PAS Pathfinder surveys: miniJPAS and J-NEP. These two surveys cover a total effective area of $\sim 1.14$ deg$^2$ with 54 Narrow Band (NB) filters across the optical range, with typical limiting magnitudes of $\sim 23$. This set of NBs allows to probe Lya emission in a wide and continuous range of redshifts. We develop a method for detecting Lya emission for the estimation of the Lya LF using the whole J-PAS filter set. We test this method by applying it to the miniJPAS and J-NEP data. In order to compute the corrections needed to estimate the Lya LF and to test the performance of the candidates selection method, we build mock catalogs. These include representative populations of Lya Emitters at $1.9<z<4.5$ as well as their expected contaminants, namely low-$z$ galaxies and $z<2$ QSOs. We show that our method is able to provide the Lya LF at the intermediate-bright range of luminosity ($\rm 10^{43.5} erg\,s^{-1} \lesssim L_{Lya} \lesssim 10^{44.5} erg\,s^{-1}$). The photometric information provided by these surveys suggests that our samples are dominated by bright, Lya-emitting Active Galactic Nuclei. At $L_{{\rm Ly}a}<10^{44.5}$ erg\,s$^{-1}$, we fit our Lya LF to a power-law with slope $A=0.70\pm0.25$. We also fit a Schechter function to our data, obtaining: Log(\Phi^* / \text{Mpc^{-3}})=-6.30^{+0.48}_{-0.70}, Log$(L^*/ \rm erg\,s^{-1})=44.85^{+0.50}_{-0.32}$, $a=-1.65^{+0.29}_{-0.27}$. Overall, our results confirm the presence of an AGN component at the bright-end of the Lya LF. In particular, we find no significant contribution of star-forming LAEs to the Lya LF at Log$(L_{\rm Lya}$ / erg\,s$^{-1}$)>43.5. This work serves as a proof-of-concept for the results that can be obtained with the upcoming data releases of the J-PAS survey.Comment: 25 pages, 15 figures, submitted to A&

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

Overmassive Black Holes in Dwarf Galaxies Out to z ∼ 0.9 in the VIPERS Survey

Supermassive black holes (SMBHs) are thought to originate from early universe seed black holes of mass M _BH ∼ 10 ^2 –10 ^5 M _⊙ and grown through cosmic time. Such seeds could be powering the active galactic nuclei (AGN) found in today’s dwarf galaxies. However, probing a connection between the early seeds and local SMBHs has not yet been observationally possible. Massive black holes hosted in dwarf galaxies at intermediate redshifts, on the other hand, may represent the evolved counterparts of the seeds formed at very early times. We present a sample of seven broad-line AGN in dwarf galaxies with a spectroscopic redshift ranging from z = 0.35 to z = 0.93. The sources are drawn from the VIPERS survey as having an Large Magellanic Cloud (LMC) like stellar mass ( M _∗ ) derived from spectral energy distribution fitting, and they are all star-forming galaxies. Six of these sources are also X-ray AGN. The AGN are powered by SMBHs of >10 ^7 M _⊙ , more massive than expected from the M _BH – M _∗ scaling relation of AGN. Based on semianalytical simulations, we find that these objects are likely overmassive with respect to their hosts since early times ( z > 4), independently of whether they formed as heavy (∼10 ^5 M _⊙ ) or light (∼10 ^2 M _⊙ ) seed black holes. In our simulations, these objects tend to grow faster than their host galaxies, contradicting models of synchronized growth. The host galaxies are found to possibly evolve into massive systems by z ∼ 0, indicating that local SMBHs in massive galaxies could originate in dwarf galaxies hosting seed black holes at higher z

The build-up of pseudo-bulges in a hierarchical universe

We study the cosmological build-up of pseudo-bulges using the L-Galaxies semi-analytical model for galaxy formation with a new approach for following separately the assembly of classical bulges and pseudo-bulges. Classical bulges are assumed to be the result of violent processes (i.e. mergers and starbursts), while the formation of pseudo-bulges is connected to the secular growth of discs. We apply the model to both the Millennium and the Millennium II simulations, in order to study our results across a wide range of stellar masses (10⁷−10¹¹.⁵M⊙). We find that z = 0 pseudo-bulges mainly reside in galaxies of Mₛₜₑₗₗₐᵣ∼10¹⁰−10¹⁰.⁵M⊙ (Mₕₐₗₒ∼10¹¹.⁵−10¹²M⊙) and we recover structural properties of these objects (e.g. sizes and bulge-to-total ratios) that are in good agreement with observational results. Tracing their formation history, we find that pseudo-bulges assembled in galaxies with a very quiet merger history, as opposed to the host galaxies of classical bulges. Regarding the bulge structure, we find that ∼30 per cent of the galaxies with a predominant pseudo-bulge feature a composite structure, hosting both a pseudo- and a classical bulge component. The classical component typically constitutes ∼10 per cent of the total bulge galaxy mass. When looking at the properties of the host galaxies, we find that z = 0 pseudo-bulges are hosted by main-sequence galaxies, characterized by a stellar population which is generally younger compared to the one of the hosts of classical bulges.ISSN:0035-8711ISSN:1365-296