Seven very luminous galaxies were examined to determine the contribution of active nuclei to their luminosity, the nature of their stellar population, and the validity of previous measurements of their H₂ content. Spectra of the 2.3 μm bands of CO were used to measure the stellar velocity dispersion, and hence the mass in the central regions. The bolometric luminosity, ionizing continuum luminosity, CO index, and 2.2 μm luminosity were also determined. Models of young stellar populations were compared to the observed properties of the galaxies. It was found that four of the seven galaxies have properties which are inconsistent with those of stellar populations. The active nuclei of these four galaxies produce more than half the total light of the galaxies, but less than one-third of the 2.2 μm light. The galaxies containing AGN also have young stellar populations. There is no evidence for the existence of active nuclei in the other three galaxies. The stellar populations that dominate the starlight in the galaxies have a wide range of properties. Stellar populations range in age from 10 to 65 Myr. The timescale for star formation ranges from 5 Myr to 100 Myr. The local initial mass function is ruled out for one of the four galaxies for which stellar population analysis could be done. The molecular gas masses for some very luminous galaxies determined from the ¹²CO J = 1 → 0 line are in error. The previously determined molecular gas masses are larger than the dynamical masses. The I(CO)/M(H₂) conversion factor found for Milky Way giant molecular clouds is evidently not correct for some very luminous infrared galaxies.

The recent discovery of a new population of Active Galactic Nuclei (AGN) – the Radio Loud Narrow Line Seyfert 1 (RL NLS1) galaxies – at g-ray energies by Fermi has prompted intense interest among researchers, as evidence mounts that these objects may in fact compose a new class of blazars. If RL NLS1s are indeed a new class of blazars, or at least analogous to them, then the detection of certain blazar-like properties would be expected. These properties include significant variability at all wavelengths across the electromagnetic spectrum and on timescales from minutes to years, significant & variable polarization in the radio and optical regimes, significant & variable high-energy emissions (especially in the g-ray regime), and a double-peaked structure of their spectral energy distributions. This dissertation seeks to characterize several of these properties for RL NLS1s as a class. These include the degree to which these objects are polarized and the variability of this property, the detection and characterization of these sources at g-ray energies with the Large Area Telescope aboard the Fermi spacecraft, and the degree to which these properties are interdependent. A photopolarimetric survey (the first of its kind for this class of objects) and g-ray monitoring program were conducted by the author in order to obtain the data necessary for this project. The measurements obtained via these observations are used to characterize this interesting class of objects with respect to a sample of blazars. In general, it was found that the polarizations of these objects fall between radio-quiet NLS1s and FSRQ-type blazars, and were most similar to HBL-type blazars. The 7 RL NLS1s in this sample that had been detected above a Test Statistic (TS) of 25 by Fermi/LAT were most similar to FSRQs, while 9 objects detected in the interval 9 < TS < 25 shared several properties with HBLs. Two RL NLS1s - J1443+4725 and J1644+2619 - are identified as high-confidence (TS > 25) g-ray sources for the first time, bringing the total number of members of this class firmly detected at g-ray energies to 8. The gamma-ray spectra of RL NLS1s are similar to FSRQs, though some have steeper spectra.

In this thesis I use X-ray observations to study the cores and extended structures of radio-loud AGN, to determine their structure, accretion properties and the impact they have on their surroundings. I use new Chandra data and archival XMM-Newton observations ofMarkarian 6 to look for evidence of emission from shocked gas around the external radio bubbles, using spatially resolved regions in Chandra and spectral analysis of the XMM data. The results show that the bubbles in Mrk 6 are indeed driving a shock into the halo of the host galaxy, with a Mach number of 3.9. I also find that the spectrum of the AGN has a variable absorbing column, which changes from 8 × 1021 atoms cm−2 to 3 × 1023 atoms cm−2 on short timescales (2-6 years). This is probably caused by a clump of gas close to the central AGN, passing in front of us at the moment of the observation. Using new and archival Chandra observations of the Circinus galaxy, I match them to pre-existing radio, infrared and optical data to study the kpc-scale emission. As for Mrk 6, I find that the radio bubbles in Circinus are driving a shock into the interstellar medium of the host galaxy, with Mach numbers M 2.7–3.6 and M 2.8–5.3 for the W and E shells respectively. Comparing the results with those we previously obtained for Centaurus A, NGC 3801 and Mrk 6, I show that the total energy in the lobes (thermal+kinetic) scales approximately with the radio power of the parent AGN. The spatial coincidence between the X-ray and edge-brightened radio emission in Circinus resembles the morphology of some SNR shocks, a parallel that has been expected for AGN, but has never been observed before. I investigate what underlying mechanisms both types of systems may have in common, arguing that, in Circinus, the edge-brightening in the shells may be accounted for by a B field enhancement caused by shock compression, but do not preclude some local particle acceleration. I also carry out a systematic study of the X-ray emission from the cores in the 0.02 < z < 0.7 2Jy sample, using Chandra and XMM-Newton observations. I combine the results with the mid-IR, optical emission line and radio luminosities, and compare them with those of the 3CRR sources, to show that the low-excitation objects in our sample show all the signs of radiatively inefficient accretion. I study the effect of the jet-related emission on the various luminosities, confirming that it is the main source of soft X-ray emission for our sources. I also find strong correlations between the accretion-related luminosities, and identify several sources whose optical classification is incompatible with their accretion properties. I derive the bolometric and jet kinetic luminosities for the sample and find a difference in the total Eddington rate between the low and high-excitation populations, with the former peaking at 1 per cent and the latter at 20 per cent Eddington. There is, however, an overlap between the two, indicating that a simple Eddington switch may not be possible. The apparent independence of jet kinetic power and radiative luminosity in the highexcitation population in our plots allows us to test the hypothesis in which jet production and radiatively efficient accretion are in fact independent processes that can coexist in high-excitation objects.

The two SCUBA HAlf-Degree Extragalactic Survey (SHADES) fields are amongst the richest places in the sky in terms of multi-wavelength coverage. They comprise an eastern section of the Lockman Hole (LH) and the central portion of the Subaru- XMM/Newton Deep Field (SXDF). In this thesis, I have obtained extremely deep, multi-frequency radio imaging of the SHADES fields using the GiantMetre-wave Radio Telescope (GMRT) and the Very Large Array (VLA), at 610MHz and 1.4GHz, respectively. These data are used to analyse the nature of the sub-milliJansky (sub-mJy) radio population, which has been hotly debated in the last few years: are they powered by star-forming or nuclear activity? To tackle the problem, I employ different approaches making use of the large variety of multi-wavelength data in the SHADES fields. I begin by analysing the spectral index, α610MHz 1.4GHz , of radio sources detected in the LH, to explore the dominant emission mechanism. Based on a robust 10 σ detection criterion, I find a constantmedian spectral index of α610MHz 1.4GHz ≈ −0.6 to −0.7 for sources between S1.4GHz ≈ 200 μJy and 10mJy. This result suggests that the galaxy population in the sub-mJy regime is powered by optically-thin synchrotron emission – starforming galaxies or lobe-dominated active galactic nuclei (AGN). Making use of X-ray observations in the LH, I show that the fraction of radio sources detected in the hard X-ray band (between 2 and 10 keV) decreases from 50 to 15 per cent between S1.4GHz ≈ 1mJy and . 100 μJy, which strongly suggests a transition from AGN to star-forming galaxies. Based on the deep, multi-wavelength coverage of the SXDF, I explore the behaviour of the far-infrared (FIR)/radio correlation as a function of redshift. I combine the q24 factor – the logarithmic flux density ratio between Spitzer 24-μm and VLA 1.4- GHz flux densities – with available photometric redshifts and find strong evidence that the correlation holds out to z ≈ 3.5. Based on M82-like k-corrections and using a high-significance (S1.4GHz > 300 μJy) radio sub-sample, I find a mean and scatter of q24 = 0.71 ± 0.47. Monte-Carlo simulations based on these findings show that fewer sources deviate from the correlation at fainter flux densities (i.e. fewer radioloud AGN). I predict that the radio-loud fraction drops from 50 per cent at ∼ 1mJy to zero at . 100 μJy. The validity of the FIR/radio correlation out to very high redshifts adds credibility to identifications of sub-millimetre (submm) galaxies (SMGs) made at radio wavelengths. Based on a sample of 45 radio-identified SMGs in the LH, I find a median radio spectral index of α610MHz 1.4GHz = −0.72 ± 0.07, which suggests that optically-thin synchrotron is the dominant radio emission mechanism. Finally, as anAppendix I include a theoretical treatment that constrains the average geometry of the dusty, torus-like structures believed to obscure a large fraction of the AGN population. I use the distribution of column densities (NH) obtained from deep ∼ 1Msec X-ray observations in the Chandra Deep Field South. I find that to reproduce the wide observed range of NH, the best torus model is given by a classical “donut”- shaped distribution with an exponential angular dependency of the density profile.

All massive nearby galaxies, including our own, host supermassive black holes. Active galactic nuclei (AGN) are seen when such black holes accrete, and when they produce powerful jets of synchrotron-emitting plasma, they are termed radio-loud AGN. The close correlation between black hole mass and galaxy bulge mass in elliptical galaxies indicates that AGN feedback may be the key to the regulation of galaxy formation. It is thus necessary to fully understand the structure of AGN, the way that they are fuelled, and their duty cycle, in order to study the feedback processes and get a clear picture of galaxy formation. In this thesis, independent methods are developed to constrain the accretion disk and radio jet angles to the line of sight. H IX emission from a sub-sample of high-redshift quasars is measured from near-infrared spectroscopy and modelled as sums of different components, including the characteristic double-peaked profile which results from a thin, rotating accretion disk. Comparing the models using Bayesian evidence, almost all quasars were found to have infrared spectra consistent with the presence of a disk. The jet inclination angles of the same set of quasars were constrained by fitting a model, including the effect of Doppler boosting and the receding torus model for dust obscuration, to the radio \ spectral energy distribution. The fitted disk and jet angles correlate strongly, and are consistent with a model in which the radio jets are launched orthogonally to the plane of the accretion disk, as expected if the jet is powered by energy drawn from the spin of the black hole. Both disk and jet angles correlate with the observed linear source size, which is a projection effect; when deprojected using the fitted angles, the distribution of source sizes agrees with a scenario in which the sources expand into the surrounding medium at a constant rate up to ~ 1 Mpc and then shut off, probably as the nuclei become quiescent. The accretion disk angle was found to correlate weakly with the low-frequency radio luminosity, which provides direct, albeit tenuous, evidence for the receding torus model.

Supermassive black holes (SMBH) are now thought to exist at the center nearly all massive galaxies. Not only are they thought to be ubiquitous, but it was also discovered nearly two decades ago that the mass of these SMBHs correlate strongly with properties of their host galaxies including bulge stellar velocity dispersion (MBH-sigma) and bulge luminosity (MBH-Lbulge). This correlation was not expected due to the tiny size of the SMBH gravitational sphere of influence compared to the size of the host galaxy, and imply a connection between the two, but this connection is still not well-understood. One step toward understanding this connection is to accurately measure the masses of these black holes. Two of the most common direct SMBH mass measurement techniques are stellar dynamical modeling (SDM), which generally only applies to quiescent galaxies, and reverberation mapping (RM), which can only be applied to active galactic nuclei (AGN) that exhibit broadened emission lines. Due to the unknown geometry of the region that produces these broad lines, the whole RM sample of black hole masses generally needs to be multiplied by a constant called the f-factor to bring it into agreement with the SDM sample on the MBH-sigma relation. It is unknown how well this f-factor, being a population average, applies to individual RM masses. It would therefore be useful to measure an SMBH mass with both methods simultaneously to test whether they produce the same black hole mass. However, because the RM and SDM techniques usually apply to galaxies that are not possible for both, this has only been attempted twice before (NGC 3227 and NGC 4151). The purpose of this dissertation is to apply SDM to the SMBH at the center of NGC 6814 for which there already exists an RM mass. This makes it only the third broad-lined AGN for which an SDM mass has been derived. In order to perform SDM accurately, the distance to the galaxy needs to be well-constrained as the error in the SDM mass scales linearly with distance. Because no adequate distance measurements already exist, the first half of this dissertation is devoted to deriving a Cepheid distance to NGC 6814 from V- and I-band HST WFC3 time series photometry. We measure the distance to NGC 6814 to be 17.54 +1.44/-1.33 Mpc. In the second half, we incorporate that distance measurement into our stellar dynamical modeling on Gemini NIFS+Altair IFU data of NGC 6814's central 1.55''x1.55''. We derive a mass of 1.19 +37.57/-1.17 x108 solar masses, and best fit mass-to-light ratio of 0.948 +0.032/-0.208 in solar units. This mass is nearly an order of magnitude larger than the RM mass but has a 3-sigma range spanning nearly three orders of magnitude. We describe possible reasons for our larger-than-expected mass value, such as the existence of a bar, which would not be well-modeled by an axisymmetric dynamical code. Finally, we describe future steps that may be taken to better constrain the mass, such as creating more models to further explore parameter space.

Nesse trabalho, foi feito o tratamento e a análise de cubos de dados de 8 núcleos ativos de galáxias próximos, no óptico e no infravermelho. O tratamento e a análise de todos os cubos de dados foram feitos utilizando-se uma série de metodologias específicas, muitas das quais foram desenvolvidas nos últimos anos pelo grupo de trabalho do autor. A análise de todos os cubos de dados foi feita com quatro objetivos principais: análise da fenomenologia geral nos arredores do AGN com a Tomografia PCA; análise das populações estelares, da emissão térmica de poeira e do featureless continuum nos arredores do AGN com uma síntese espectral feita com o software Starlight; análise da cinemática estelar e do gás ao redor do buraco negro central e, em alguns casos, simulação com o objetivo de se determinar a massa do buraco negro; análise dos mecanismos de excitação e ionização do gás ou da emissão de hidrogênio molecular. / In this work, we have treated and analyzed data cubes of 8 nearby active galactic nuclei, in the optical and in the infrared. All data cube treatment and analysis were performed using a series of specific methodologies, many of which were developed in the last few years by the author\'s working group. The analysis of all data cubes was performed with four main objectives: analysis of the general phenomenology of the AGN environment, using PCA Tomography; analysis of the stellar populations, of the thermal emission from dust and of the featureless continuum in the vicinity of the AGN, with a spectral synthesis performed with the Starlight software; analysis of the stellar and gas kinematics around the central black hole and, in some cases, simulations with the purpose of determining the mass of the black hole; analysis of the excitation and ionization mechanisms of the gas or of the emission from molecular hydrogen.

No description available.

L'astronomie de haute énergie se concentre sur l'étude des phénomènes les plus violents de l'univers à partir d'observations dans une gamme d'énergie allant des rayons X aux rayons gammas de très hautes énergies (1 keV - 100 TeV). Ces phénomènes incluent par exemple les explosions de supernovae et leurs vestiges, les pulsars et les nébuleuses de vent de pulsar ou encore la formation de jets ultrarelativistes au niveau des noyaux actifs de galaxie. Leur compréhension fait appel à des processus de physique des particules bien connus qui seront décrits dans cette thèse. Par l'intermédiaire de photons de haute énergie, l'étude de ces phénomènes de haute énergie ouvre donc une fenêtre originale pour la recherche de physique au delà du modèle standard. Les concepts relatifs à l'émission et la propagation de photons de haute énergie sont introduits dans cette thèse et appliqués à l'étude de l'émission de sources extragalactiques ainsi que du fond de lumière extragalactique, affectant la propagation des photons de haute énergie dans l'univers. Dans le cadre de cette thèse, ces sources extragalactiques de photons de haute énergie sont observées afin de rechercher de nouveaux bosons légers, tels que ceux appartenant à la famille des particules de type axion (PTA). Les bases théoriques décrivant cette famille de particules sont présentées, ainsi que la phénoménologie associée. Notamment, en raison de leur couplage à deux photons, ces particules ont la propriété d'osciller avec des photons en présence de champ magnétique externe. Une nouvelle signature de la présence de telles oscillations dans des champs magnétiques turbulents, sous la forme d'irrégularités stochastiques dans le spectre en énergie, est étudiée et discutée. Cette signature est appliquée à la recherche de PTA avec le réseau de télescopes HESS, permettant d'obtenir pour la première fois des contraintes sur ces modèles à partir d'observations en astronomie gamma. La recherche de la même signature dans des observations en rayons X permet d'améliorer les contraintes actuelles pour les PTA de très basse masse et l'extension de ces contraintes à des modèles de modification de la gravité comme explication de la nature de l'énergie noire est également évoquée. Enfin, la recherche de PTA avec l'instrument d'astronomie gamma du futur, CTA, est discutée; en particulier, une nouvelle observable est proposée qui tire partie du grand nombre de sources attendu avec cet instrument. / High-Energy astronomy studies the most violent phenomena in the universe with observations in a large spectrum of energies ranging from X rays to very high energy gamma rays (1 keV - 100 TeV). Such phenomena could be for instance supernovae explosions and their remnants, pulsars and pulsar wind nebulae or ultra relativistic jets formation by active galactic nuclei. Understanding these phenomena requires to use well-known particle physics processes. By means of high energy photons, studying such phenomena enables one to search for physics beyond the standard model. Concepts regarding the emission and propagation of high-energy photons are introduced and applied to study their emission by extragalactic sources and to constrain the extragalactic background light which affects their propagation. In this thesis, these high-energy extragalactic emitters are observed in order to search for new light bosons such as axion-like particles (ALPs). The theoretical framework of this family of hypothetical particles is reviewed as well as the associated phenomenology. In particular, because of their coupling to two photons, ALPs oscillate with photons in an external magnetic field. A new signature of such oscillations in turbulent magnetic fields, under the form of stochastic irregularities in the source energy spectrum, is introduced and discussed. A search for ALPs with the HESS telescopes with this new signature is presented, resulting in the first constraints on ALPs parameters coming from high-energy astronomy. Current constraints on ALPs at very low masses are improved by searching for the same signature in X-ray observations. An extension of these constraints to scalar field models for modified gravity in the framework of dark energy is then discussed. The potential of the search for ALPs with CTA, the prospected gamma-ray astronomy instrument, is eventually studied; in particular, a new observable is proposed that relies on the high number of sources that are expected to be discovered with this instrument.

Motivated by recent successes in linking the kinetic power of relativistic jets in active galactic nuclei (AGN) to the low-frequency, isotropic lobe emission, I have re-examined the blazar and radio-loud AGN unification scheme through careful analysis of the four parameters we believe to be fundamental in producing a particular jet spectral energy distribution (SED): the kinetic power, accretion power, accretion mode, and orientation. In particular, I have compiled a multi-wavelength database for hundreds of jet SEDs in order to characterize the jet spectrum by the synchrotron peak output, and have conducted an analysis of the steep lobe emission in blazars in order to determine the intrinsic jet power. This study of the link between power and isotropic emission is likely to have a wider applicability to other types or relativistic jet phenomena, such as microquasars. Based on a well-characterized sample of over 200 sources, I suggest a new unification scheme for radio-loud AGN (Meyer et al. 2011) which compliments evidence that a transition in jet power at a few percent of the Eddington luminosity produces two types of relativistic jet (Ghisellini, et al., 2009). The `broken power sequence' addresses a series of recent findings severely at odds with the previous unification scheme. This scheme makes many testable predictions which will can be addressed with a larger body of data, including a way to determine whether the coupling between accretion and jet power is the currently presumed one-to-one correspondence, or whether accretion power forms an upper bound, as very recent observations suggest (Fernandes et al. 2011). This work is a first step toward a unified understanding of the relativistic jets found in radio-loud active galactic nuclei (AGN) and their connection to accretion onto the super-massive black holes from which they emanate.