京都大学 / 新制・課程博士 / 博士(理学) / 甲第25117号 / 理博第5024号 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 上田 佳宏, 准教授 岩室 史英, 教授 前田 啓一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Black hole jets and accretion discs are the most extreme objects in modern astrophysics whilst dark energy is undoubtedly the most mysterious. This thesis focuses on understanding these three topics. The majority of this thesis is dedicated to investigating the structure and properties of black hole jets by modelling their emission. I develop an inhomogeneous jet model with a magnetically dominated parabolic accelerating base, transitioning to a slowly decelerating conical jet, with a geometry set by radio observations of M87. This model is able to reproduce the simultaneous multiwavelength spectra of all 38 Fermi blazars with redshifts in unprecendented detail across all wavelengths. I constrain the synchrotron bright region of the jet to occur outside the BLR and dusty torus for FSRQs using the optically thick to thin synchrotron break. At these large distances their inverse-Compton emission originates from scattering CMB photons. I find an approximately linear relation between the jet power and the transition region radius where the jet first comes into equipartition, transitions from parabolic to conical and stops accelerating. The decreasing magnetic field strength and increasing bulk Lorentz factor with jet power are the physical reasons behind the blazar sequence. I calculate the conditions for instability in a thin accretion disc with an α parameter which depends on the magnetic Prandtl number, as suggested by MHD simulations. The global behaviour of the instability induces cyclic flaring in the inner regions of the disc, for parameters appropriate for X-ray binary systems, thereby offering a potential solution to a long standing problem. Finally, I calculate the effect of an interacting quintessence model of dark energy on cosmological observables. I find that a scalar-tensor type interaction in the dark sector results in an observable increase in the matter power spectrum and integrated Sachs-Wolfe effect at horizon scales.

The local universe is dominated by quiescent galaxies with little or no ongoing star formation. Once star formation has been shut down in a possible quasar phase, energy feedback in the form of outflows from a supermassive black hole (SMBH) accreting at a low rate is one of the leading candidates for heating up or removing gas accreted afterwards. In this work we performed hydrodynamic simulations of radiatively inefficient accretion flows around supermassive black holes and investigate the generation of outflows by the accretion flow. We found that hot accretion flows can produce powerful subrelativistic winds that carry considerable amounts of energy away and they can provide feedback inside the host galaxy. / O universo local é dominado por galáxias quiescentes com pouca, ou nenhuma, taxa atual de formação estelar. Uma vez que a formação estelar é suprimida numa possível fase de quasar do núcleo ativo da galáxia, o feedback de energia na forma de outflows do buraco negro supermassivo acretando a pequenas taxas é um dos principais candidatos a aquecer ou remover o gás do sistema. Nesse trabalho, executamos simulações hidrodinâmicas de escoamentos acretivos radiativamente ineficientes ao redor de buracos negros supermassivos e investigamos a geração de outflows pelo escoamento. Encontramos que escoamentos acretivos quentes podem produzir ventos subrelativísticos poderosos que carregam para fora consideráveis quantidades de energia e que podem providenciar feedback dentro da galáxia hospedeira.

There exists many astronomical objects that vary in brightness. Objects such as variable stars like the Cepheids that periodically expands and contracts their outer layers, or the active galactic nuclei (AGN) where accretion of matter into a black hole generates a often varying brightness. Several candidates for being such variable objects have been identified as a result of the Vanishing and Appearing Stuff during a Century of Observations (VASCO) project. These candidates were then narrowed down to a handful that showed variability towards the infrared part of the spectrum. This bachelor’s thesis then aims to look further into these candidates using various databases and catalogues taking data from several sky surveys (SDSS, 2MASS etc). This is done to get better overview of the objects lightcurve over a bigger part of the spectrum, to establish whether the variability is real or a result from errors and to form a hypothesis of what kind of objects they could be. The result obtained from the data from the surveys points towards all the objects being real variable objects. The hypothesis is that all the objects are AGN’s that vary in brightness. / Det existerar många olika astronomiska objekt som varierar i ljusstyrka. Allt från variabla stjärnor som Cepheiderna som periodvis expanderar och kontraherar dess yttre skikt, till aktiva galaxkärnor där ackretion av materia in i ett svart hål genererar en ofta varierande ljusstyrka. Ett flertal kandidater för just sådana varierande objekt har identifierats som ett resultat av VASCO projektet. Dessa kandidater har sedan skalats ner till en handfull mängd kandidater som visade variation mot den infraröda delen av spektrumet. Detta kandidatarbete siktar på att vidare undersöka dessa kandidater genom att använda diverse astronomiska databaser och kataloger för att få data från flera kartläggningsprojekt (t.ex. SDSS, 2MASS etc). Detta är gjort för att få en bättre överblick över objektens ljuskurvor över en större del av spektrumet, att fastställa ifall objekten är riktiga variabla objekt eller uppstått på grund av diverse fel, samt att framställa en hypotes för vad det är för typ av objekt de kan vara. Resultaten från undersökningarna pekar på att alla objekten är riktiga variabla objekt. Hypotesen är att alla av objekten är aktiva galaxkärnor som varierar i ljusstyrka.

Les Noyaux actifs de galaxie (AGN) incluent les sources quasi stables les plus énergétiques connues dans l'univers jusqu'à aujourd’hui. Du fait de leur distance, de leur haute luminosité et de leur petite taille, leurs régions intérieures ne sont pas directement résolvables avec les télescopes actuels. C’est pour ces raisons que nous avons besoin de techniques d’observation indirectes et de modèles théoriques pour discerner leur structure. Dans cette optique, le rôle de la polarimétrie est crucial. Elle a été ces dernières années la méthode clé qui a permis de développer le modèle unifié des AGN et pourrait, à l’avenir, nous offrir des nouveaux éléments pour sonder les régions des AGN irrésolues. Dans cette thèse, j’ai conduit des simulations sur les transferts radiatifs relatifs aux rayonnements continus émis des différentes régions intérieures des AGN en utilisant la nouvelle technique de cartographie de réverbération polarimétrique. Ce travail a été inspiré par les recherches de Gaskell et al. (2012). Le but de cette recherche est de fournir des modèles théoriques sur les différents composants des AGN en considérant le rayonnement polarisé en fonction du temps. La polarisation induite par la diffusion a été modélisée et différentes géométries de poussières circumnucléaires ont été testées. Les résultats incluent les effets de l’agrégation des poussières et différentes compositions de poussière. Pour étendre le modèle, les effets complémentaires des vents ionisés s’étirant en direction des pôles ont également été étudiés ainsi que ceux de l’anneau de diffusion équatorial théorique, avec pour postulat qu'il explique l’angle de polarisation observé dans les pôles des AGN. Les simulations ont été exécutées en utilisant une version du code STOKES incluant la dépendance temporelle. Il sera possible d'étendre ce travail à l'avenir. Les prochaines étapes suggérées incluront des raies d'émission aux modélisations ainsi que plus de complexité concernant la géométrie et la distribution de la poussière et/ou des électrons dans les régions de diffusion. Ce travail sera important pour profiter de futures données observationnelles systématiques avec un bon échantillonnage temporel. / Active galactic nuclei (AGN) include the most powerful quasi-steady sources of energy known to date in the universe. Due to their distance, high brightness and small size, their inner regions are not directly resolvable with current telescopes. This is the reason why indirect techniques and theoretical models are needed to discern their structure. In this scenario the role of polarimetry is crucial. In the past it was the key method that led to the development of the Unified Model of AGN and in the future, it may give us new clues to probe unresolved AGN regions. In this thesis, I conducted radiative transfer simulations for continuous radiation of different inner regions of the AGN using the new technique of polarimetric reverberation mapping. This work has been inspired by the work of Gaskell et al. (2012). The goal of this research is to provide theoretical models of the different components of the AGN considering time-dependent polarized radiation. Scattering induced polarization has been modeled and different circumnuclear dust geometries have been explored. The results include the effects of clumpiness and different dust compositions. To further extend the model, the effects of additional extended ionized winds along the polar direction have also been explored as well as the putative equatorial scattering ring postulated to explain the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code. It will be possible to extend this work in the future. Suggested future steps are including emission lines in the models, as well as more complexity in the geometry and distribution of dust and/or electrons in the scattering regions. This work will be important for taking advantage of systematic future observational data with good temporal sampling.

We present a study of high-resolution long-slit spectra of the Narrow-Line Regions (NLRs) of NGC 4151 (a Seyfert 1 galaxy) and NGC 1068 (a Seyfert 2 galaxy) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). The spectra were retrieved from the Multimission Archive at Space Telescope (MAST) and were obtained from five and seven orbits of HST time resulting in five and seven parallel slit configurations at position angles of 52 degrees and 38 degrees for NGC 4151 and NGC 1068 respectively. The spectra have a spatial resolution of 0.2 arcsecond across and 0.1 arcsecond along each slit. Observations of [O III] emission from the NLRs were made using the medium resolution G430M grating aboard HST. The spectral resolving power of the grating, R~9000, resulted in the detection of multiple kinematic components of the [O III] emission line gas along each slit. Radial velocities of the components were measured using a Gaussian fitting procedure. Biconical outflow models were generated to match the data and for comparison to previous models done with lower dispersion observations. The general trend is an increase in radial velocity roughly proportional to distance from the nucleus, followed by a linear decrease after roughly 100 pc. This is similar to that seen in other Seyfert galaxies, indicating common acceleration and deceleration mechanisms. The full-width at half-maximum (FWHM) of the emission lines reaches a maximum of 1000 km/s near the nucleus, and generally decreases with increasing distance to about 100 km/s in the extended narrow-line region (ENLR), starting at about 400 pc from the nucleus. In addition to the bright emission knots, which generally fit our model, there are faint high velocity clouds that do not fit the biconical outflow pattern of our kinematic model. A comparison of our observations with high-resolution radio maps shows that the kinematics of the faint NLR clouds may be affected by the radio lobes that comprise the inner jet. However, the bright NLR clouds show a smooth transition across the radio knots in radial velocity and velocity dispersion plots and remain essentially undisturbed in their vicinity, indicating that the radio jet is not the principal driving force on the outflowing NLR clouds. A dynamical model was developed for NGC 1068; it includes forces of radiation pressure, gravity, and drag due an ambient medium, simultaneously acting on the NLR clouds. The velocity profile from this model was too steep to fit the data, which show a more slowly increasing velocity profile. Gravity alone was not able to slow down the clouds but with the drag forces included, the clouds could slow down, reaching systemic velocities at distances that depend on the column densities of the NLR gas and density of the intercloud medium. A biconical model using the geometric parameters from our kinematic fit, and the velocity law from the dynamic fit, was used to match the data. The resulting dynamic model represented a poor fit to the data, indicating the need for additional dynamical considerations.

Active Galactic Nuclei (AGNs) are the most mystic objects in the universe. They are usually very far away from our Galaxy, which means that they are ancient objects. They are also luminous and have unique features in their spectra. Studying AGNs helps understanding the early universe and the evolution of galaxies. This Dissertation aims to research the structure of AGNs and the cooling function in the AGNs environment. I first investigate what optical/ultraviolet spectroscopic features would be produced by Broad-line Region (BLR) clouds crossing our line of sight to the accretion disk, the source of the optical/UV continuum. This research, prompted by recent X-ray observations, suggests that single cloud has little effect on the optical/UV spectrum. However, an ensemble of clouds produces a strong distinctive feature between the Lyman limit and Lyα. The extent of these features indicates the line-of-sight covering factor of clouds and may explain the ubiquitous AGN spectral break around 1100Å. I next study, considering the physical parameters of AGNs, how the gas cooling function changes at high temperature (T > 104 K) over a wide range of density (nH < 1012 cm−3) and metallicity (Z < 30Z⊙). I find that both density and metallicity change the ionization status of the gas. I provide numerical cooling functions by describing the total cooling as a sum of four parts: that due to H&He, the heavy elements, electron-electron bremsstrahlung, and grains. Finally, I also provide a function giving the electron fraction, which can be used to convert the cooling function into a cooling rate. Last, I extend the cooling-function study to the seldom-explored low-temperature range (T < 104 K). For primordial gas, gas lacking elements heavier than B, I find that radiative attachment and Compton recoil are important cooling processes when the gas kinetic temperature is lower than the temperature of the cosmic microwave background. I also find that collisional de-excitation of HD and H2 is not important above 1000K unlike claims of previous studies. For the dust-free solar case, we identify water as the dominant coolant in high density-environments. We also analyze the parameter ranges where metal, metal molecules, or all molecules, dominate the total cooling. We provide the density, above which the metal or metal molecules become the dominant coolants, as a function of temperature and metallicity. For the ISM case, with dust and depleted abundances, we find that dust does not directly cool the gas. Rather, dust modifies he cooling by affecting the chemistral balance. Similar to the high-temperature case, I also provide numerical cooling data.

When probing the inner structures of unresolved astrophysical sources, spectropolarimetry has proven to be a solid tool, both independent and complementary to spectral and timing analyses. In this thesis, I theoretically explore the polarization of Active Galactic Nuclei (AGN), which are powered by accretion onto supermassive black holes and often reveal significant mass outflows. Their emission is strongly anisotropic and the standard model of AGN postulates that the anisotropy is caused by a confinement of the radiation in the funnel of an obscuring body of circumnuclear dust; the radiation is thus forced to escape along the funnel where it photo-ionizes conically shaped outflows. The asymmetrical configuration explains an observational dichotomy where AGN properties are characterized according to the observer's line-of-sight. However, AGN observations differ significantly from one waveband to another and the broadband validity of the unified model has to be tested by a method that gives strong constraints on the AGN morphology. In this thesis, I subsequently investigate how morphological and composition constraints on the different substructures in thermal, radio-quiet Active Galactic Nuclei can be deduced from optical, UV and X-ray polarization properties.

Through the work on X-ray and gamma-ray data of AGN I contributed significantly to the progress in the unification of AGN since I finished my PhD in 2000. <p> The study of the evolutionary behaviour of X-ray selected blazars (Beckmann & Wolter 2001; Beckmann et al. 2002, 2003b; Beckmann 2003) shows that their evolution is not as strongly negative as indicated by previous studies. The overall luminosity function is consistent with no evolution in the 0.1−2.4 keV band as seen by ROSAT/PSPC. There is still a difference compared to the luminosity function of FSRQ and LBL, which seem to show a positive evolution, indicating that they have been more luminous and/or numerous at cosmological distances. We indicated a scenario in order to explain this discrepancy, in which the high luminous FSRQ develop into the fainter LBL and finally into the BL Lac objects with high frequency peaks in their spectral energy distribution but overall low bolometric luminosity. <p> Studying the variability pattern of hard X-ray selected Seyfert galaxies, we actually found differences between type 1 and type 2 objects, in the sense that type 2 seemed to be more variable (Beckmann et al. 2007a). This breaking of the unified model is caused by the different average luminosity of the absorbed and unabsorbed sources, as discussed in Sect. 4.7.3. This can be explained by a larger inner disk radius when the AGN core is most active (the so-called receding disc model). <p> The work on the sample characteristics of hard X-ray detected AGN also led to the proof that the average intrinsic spectra of type 1 and type 2 objects are the same when reflection processes are taken into account (Beckmann et al. 2009d). This also explains why in the past Seyfert 2 objects were seen to have harder X-ray spectra than Seyfert 1, as the stronger reflection hump in the type 2 objects makes the spectra appear to be flatter, although the underlying continuum is the same. <p> Further strong evidence for the unification scheme comes from the observation of a fundamental plane which connects type 1 and type 2 objects smoothly (Beckmann et al. 2009d). In addition, in the case of the Seyfert 1.9 galaxy MCG-05-23-016 I showed that the spectral energy distribution of this source and its accretion rate is similar to that of a Galactic binary (Beckmann et al. 2008a). <p> Throughout the studies I have shown that the intrinsic spectral shape appears to be very stable on weeks to year time scale (Beckmann et al. 2004d, 2005b, 2007b, 2008a). This implies that the overall geometry of the AGN over these time scales did not change dramatically. The variations in intensity can then be explained in two ways: either the amount of material emitting the hard X-rays varies, or the amount of plasma visible to the observer varied, e.g. through different orientation of the disk with respect to the observer. In an upcoming paper we will show though, that NGC 4151 indeed also shows different spectral states, similar to the low-hard versus high-soft spectra in Galactic black hole binaries (Lubinski et al. 2010). A similar result seems to emerge from our INTEGRAL studies on NGC 2110 (Beckmann & Do Cao 2011). For INTEGRAL's AO-8 I have submitted a proposal in order to study spectral states in the Seyfert 2 galaxy NGC 2992, which seems to show a state change over the past 5 years as seen in Swift/BAT longterm monitoring. <p> The work on the luminosity function of AGN at hardest X-rays (Beckmann et al. 2006d) had a large impact on our understanding of the cosmic X-ray background. As this was the first study of its kind, it showed for the first time that indeed the fraction of highly obscured Compton thick AGN is much lower than expected before the launch of INTEGRAL and Swift. The X-ray luminosity function we revealed is indeed not consistent with the source population seen by INTEGRAL (Beckmann et al. 2006a, 2009d; Sazonov et al. 2007) and Swift (Tueller et al. 2008) being the only contributors to the cosmic hard X-ray background. Thus other sources outside the parameter space observable by these missions have to contribute significantly to the cosmic X-ray background. Our work on the luminosity function triggered several other studies on this issue. The subsequent derived luminosity functions by other groups (Sazonov et al. 2007; Tueller et al. 2008; Paltani et al. 2008) are consistent with our findings. <p> This also gave rise to an increased interest in the exact shape of the Cosmic X-ray background around its peak at 30 keV, triggering several attempts to a new measurement. Background studies were presented based on a Earth-occultation observation by INTEGRAL (Churazov et al. 2007, 2008; Türler et al. 2010) and by Swift (Ajello et al. 2008). <p> The understanding of the emission processes in AGN requires knowledge over a wide range of the spectral energy distribution (SED). In studies using CGRO/EGRET and Fermi/LAT data I derived the SED for blazars and non-blazars towards the gamma-ray range (Beckmann 2003; Beckmann et al. 2004b, 2010b). The work on the LAT data not only presented the gamma-ray detection of five gamma-ray blazars (QSO B0836+710, RX J1111.5+3452, H 1426+428, RX J1924.8-2914, and PKS 2149-306) for the first time, but also showed the potential in the combination of INTEGRAL and Fermi data. In the case of Cen A I derived the total energy output of the inverse Compton component based on the combined LAT, ISGRI, and JEM-X data, showing evidence for a spectral break at several hundred keV (Beckmann et al. 2010b). <br> In addition I successfully showed that gamma-ray blazars can be predicted through the study of their synchrotron branch at energies below 2 keV (Beckmann 2003 and this work). <p> Contributions of mine to research in fields other than AGN include the study of INTEGRAL detected gamma-ray bursts (e.g. Beckmann et al. 2003a, 2004a, 2008b, 2009a). Here and in collaboration with other colleagues I showed the potential of INTEGRAL data on GRB research. In the field of Galactic X-ray binaries I published one of the first Swift results on a newly discovered highly absorbed HMXB, IGR J16283-4838 (Beckmann et al. 2005a, 2006b). I also contributed significantly to analysis of many other Galactic sources, as shown in Section 4.6.1.

Using the Chandra X-ray Observatory, Martini et al. (2006) found that the AGN fraction of galaxy clusters was five times higher than previous optical studies suggested. Using visual observations only, Dressler et al. (1985) estimated the AGN fraction of field galaxies to be 5%, while that of clusters was thought to be 1%. To understand the role that the environment plays in AGN fueling, the author studied a variety of environments, ranging from the field to groups to clusters. Will the AGN fraction of groups also be higher than that of the field? The author demonstrates how the AGN fraction of groups compares to that of clusters. In the following sections, the author describes the mechanics of X-ray astronomy, the group environment, and the characteristics of active galactic nuclei. The author briefly describes the possible mechanisms for AGN fueling.