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.

Primary marine aerosol particles containing biogenic polymer microgels play a potential role for cloud formation in the pristine high Arctic summer. One of the major sources of the polymer gels in Arctic aerosol was suggested to be the surface water and more specifically, the surface microlayer (SML) of the open leads within the perennial sea ice as a result of bubble bursting at the air-sea interface.  Phytoplankton and/or ice algae are believed to be the main origins of the polymer gels. In this thesis, we examine the chemical composition of biogenic polymers, with focus on polysaccharides, in seawater and airborne aerosol particles collected during the Arctic Summer Cloud Ocean Study (ASCOS) in the summer of 2008. The main results and findings include: A novel method using liquid chromatography coupling with tandem mass spectrometry was developed and applied for identification and quantification of polysaccharides. The enrichment of polysaccharides in the SML was shown to be a common feature of the Arctic open leads. Rising bubbles and surface coagulation of polymers are the likely mechanism for the accumulation of polysaccharides at the SML. The size dependencies of airborne polysaccharides on the travel-time since the last contact with the open sea are indicative of a submicron microgel source within the pack ice.  The similarity of polysaccharides composition observed between the ambient aerosol particles and those generated by in situ bubbling experiments confines the microgel source to the open leads. The demonstrated occurrence of polysaccharides in surface sea waters and in air, with surface-active and hygroscopic properties, has shown their potential to serve as cloud condensation nuclei and subsequently promote cloud-drop activation in the pristine high Arctic. Presumably this possibility may renew interest in the complex but fascinating interactions between marine biology, aerosol, clouds and climate. / At the time of doctoral defence, the following paper was unpublished and had a status as follows: Paper 4: Manuscript

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.

Recent research has shown that secondary organic aerosols (SOA) are major contributors to ultrafine particle growth to climatically relevant sizes, increasing global cloud condensation nuclei (CCN) concentrations within the continental boundary layer (BL). This thesis contains two separate studies investigating SOA characteristics and the implications of SOA on global climate. The first study investigates two critical, but uncertain, characteristics of SOA: (1) the amount of SOA available to condense and (2) the volatility or condensational behavior of SOA. The second study investigates the effect of biological volatile organic compound (BVOC) emission changes on SOA formation from preindustrial to present day, and the effect on CCN concentrations using BVOC emission estimates over the last millennium.

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.

Aerosols have significant impacts on earth's climate and hydrological cycle. They can directly reflect the amount of incoming solar radiation into space; by acting as cloud condensation nuclei (CCN), they can indirectly impact climate by affecting cloud albedo. Our current assessment of the interactions of aerosols and clouds is uncertain and parameters used to estimate cloud droplet formation in global climate models are not well constrained. Organic aerosols attribute much of the uncertainty in these estimates and are known to affect the ability of aerosol to form cloud droplets (CCN Activity) by i) providing solute, thus reducing the equilibrium water vapor pressure of the droplet and ii) acting as surfactants capable of depressing surface tension, and potentially, growth kinetics. My thesis dissertation investigates various organic aerosol species (e.g., marine, urban, biomass burning, Humic-like Substances). An emphasis is placed on the water soluble components and secondary organic aerosols (SOA). In addition the sampled organic aerosols are acquired via different media; directly from in-situ ambient studies (TEXAQS 2006) environmental chamber experiments, regenerated from filters, and cloud water samples. Novel experimental methods and analyses to determine surface tension, molar volumes, and droplet growth rates are presented from nominal volumes of sample. These key parameters for cloud droplet formation incorporated into climate models will constrain aerosol-cloud interactions and provide a more accurate assessment for climate prediction.

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.

Made available in DSpace on 2014-10-09T12:48:22Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:22Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP