We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C II] 158 mu m fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of similar to 0.'' 3, and resolve both the dust continuum and the [C II] line emission on a few kiloparsec scales. The [C II] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C II] emitting gas. The combined data confirm the [C II] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C II] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 +/- 55 kms(-1) at a radius of 3.2 kpc with an inclination angle of 34 degrees. We measure the dynamical mass within the 3.2 kpc region to be 13.4(-5.3)(+7.8) x 10(10) M-circle dot. This yields a black-hole and host galaxy mass ratio of 0.020(-0.007)(+0.013), which is about 4(-2)(+3) times higher than that of the present-day M-BH/M-bulge ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.

We present a sample of similar to 1000 emission-line galaxies at z = 0.4-4.7 from the similar to 0.7deg(2) High-z Emission-Line Survey in the Bootes field identified with a suite of six narrow-band filters at approximate to 0.4-2.1 mu m. These galaxies have been selected on their Ly alpha (73), [O (II)] (285), H beta/[O (III)] (387) or H alpha (362) emission line, and have been classified with optical to near-infrared colours. A subsample of 98 sources have reliable redshifts from multiple narrow-band (e.g. [O (II)]-H alpha) detections and/or spectroscopy. In this survey paper, we present the observations, selection and catalogues of emitters. We measure number densities of Ly alpha, [O (II)], H beta/[O (III)] and H alpha and confirm strong luminosity evolution in star-forming galaxies from z similar to 0.4 to similar to 5, in agreement with previous results. To demonstrate the usefulness of dual-line emitters, we use the sample of dual [O (II)]-H alpha emitters to measure the observed [O (II)]/H alpha ratio at z = 1.47. The observed [O (II)]/H alpha ratio increases significantly from 0.40 +/- 0.01 at z = 0.1 to 0.52 +/- 0.05 at z = 1.47, which we attribute to either decreasing dust attenuation with redshift, or due to a bias in the (typically) fibre measurements in the local Universe that only measure the central kpc regions. At the bright end, we find that both the H alpha and Ly alpha number densities at z approximate to 2.2 deviate significantly from a Schechter form, following a power law. We show that this is driven entirely by an increasing X-ray/active galactic nucleus fraction with line luminosity, which reaches approximate to 100 per cent at line luminosities L greater than or similar to 3 x 10(44) erg s(-1).

Post-starbursts (PSBs) are candidate for rapidly transitioning from starbursting to quiescent galaxies. We study the molecular gas evolution of PSBs at z similar to 0.03-0.2. We undertook new CO (2-1) observations of 22 Seyfert PSB candidates using the Arizona Radio Observatory Submillimeter Telescope. This sample complements previous samples of PSBs by including green-valley PSBs with Seyfert-like emission, allowing us to analyse for the first time the molecular gas properties of 116 PSBs with a variety of AGN properties. The distribution of molecular gas to stellar mass fractions in PSBs is significantly different from normal star-forming galaxies in the CO Legacy Database (COLD) GASS survey. The combined samples of PSBs with Seyfert-like emission line ratios have a gas fraction distribution that is even more significantly different and is broader (similar to 0.03-0.3). Most of them have lower gas fractions than normal star-forming galaxies. We find a highly significant correlation between the WISE 12 and 4.6 mu m flux ratios and molecular gas fractions in both PSBs and normal galaxies. We detect molecular gas in 27 per cent of our Seyfert PSBs. Taking into account the upper limits, the mean and the dispersion of the distribution of the gas fraction in our Seyfert PSB sample are much smaller (mu = 0.025, sigma = 0.018) than previous samples of Seyfert PSBs or PSBs in general (mu similar to 0.1-0.2, sigma similar to 0.1-0.2).

A direct consequence of hierarchical galaxy formation is the existence of dual supermassive black holes, which may be preferentially triggered as active galactic nuclei (AGNs) during galaxy mergers. Despite decades of searching, however, dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 100 morphologically identified interacting galaxies or mergers that display red mid-infrared colors often associated in extragalactic sources with powerful AGNs. The vast majority of these advanced mergers are optically classified as star-forming galaxies, which suggests that they may represent an obscured population of AGNs that cannot be found through optical studies. In this work, we present Chandra/ACIS observations and near-infrared spectra with the Large Binocular Telescope of six advanced mergers with projected pair separations less than similar to 10 kpc. The combined X-ray, near-infrared, and mid-infrared properties of these mergers provide confirmation that four out of the six mergers host at least one AGN, with four of the mergers possibly hosting dual AGNs with projected separations less than similar to 10 kpc, despite showing no firm evidence for AGNs based on optical spectroscopic studies. Our results demonstrate that (1) optical studies miss a significant fraction of single and dual AGNs in advanced mergers, and (2) mid-infrared pre-selection is extremely effective in identifying dual AGN candidates in late-stage mergers. Our multi-wavelength observations suggest that the buried AGNs in these mergers are highly absorbed, with intrinsic column densities in excess of similar to N-H > 10(24) cm(-2), consistent with hydrodynamic simulations.

We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by several extreme flares. The ratio between the optical, X-ray and gamma-ray fluxes is very variable. The gamma-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of similar to 50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.

The reflection of the X-rays emitted from a corona of energetic particles surrounding an accreting black hole from the accretion disc is investigated in the context of probing the structure of the central regions as well as the physical processes that power some of the brightest objects seen in the Universe. A method is devised to measure the emissivity profile of the accretion disc, that is the reflected flux as a function of radius in the disc. This method exploits the variation in the Doppler and gravitational redshift of emission from different radii in the disc to fit the observed reflection spectrum as the sum of contributions from successive radii and is applied to X-ray spectra of the narrow line Seyfert 1 galaxies 1H 0707-495, IRAS 13224-3809 and MCG-6-30-15 as well as the Galactic X-ray binary, Cygnus X-1. This illumination pattern of the accretion disc is a sensitive probe of the geometry of the corona that is illuminating the disc. A formalism is developed in which systematic ray tracing simulations can be run between X-ray emitting coronae and the accretion disc for a range of source geometries and other physical parameters, allowing observable data products to be simulated that can be directly compared to data from astrophysical black holes, in order to determine how these parameters affect the observed data, allowing them to be constrained observationally. The measured emissivity profiles are found to be in agreement with those expected theoretically and it is also discovered that the measured emissivity profile can be used to determine the radial extent of the X-ray emitting corona above the accretion disc. The X-ray emitting coronae are located and their radial extents constrained in 1H 0707-495, IRAS 13224-3809 and MCG-6-30-15, while the insight gained into accretion disc emissivity profiles from ray tracing simulations allows the low flux state that 1H 0707-495 was seen to drop in to in January 2011 to be explained in terms of a collapse of the X-ray emitting corona to a confined region around the central black hole. The rapid variability of the X-ray emission from accreting black holes is exploited in the use of reverberation time lags, where variability in the continuum is seen to lead that in its reflection from the accretion disc, to measure the distances between the X-ray emitting corona and the reflector. Ray tracing calculations are developed to simulate lag spectra that can be measured in X-ray observations to provide a means of constraining the extent and geometry of the corona, complimentary to the use of the emissivity profiles. Combining these methods, the X-ray emitting coronae are constrained to extend radially outward a few tens of gravitational radii over the accretion disc, while extending vertically a few gravitational radii above the plane of the disc. Furthermore, it is demonstrated how measured lag spectra can be used to understand the propagation of luminosity fluctuations through the extent of the corona and techniques are developed for analysing energy-resolved variability analysis that will be possible with future generations of X-ray telescopes. Finally, these methods, along with theoretical insight gained form ray tracing simulations, are applied to X-ray spectra extracted from 1H 0707-495 during periods of low and high flux during the observations. Evidence is found for the expansion of the corona along with a drop in the average energy density as the X-ray luminosity increases followed by its contraction as the luminosity decreases on timescales of hours.

The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured active galactic nuclei (AGNs) at high accretion luminosities, L-X(2-10 keV) greater than or similar to 10(44) erg s(-1), and out to redshift z approximate to 1.5. The sample covers an area of about 14 deg(2) and provides constraints on the space density of powerful AGNs over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, N-H approximate to 10(24) cm(-2). The fraction of obscured Compton-thin (N-H = 10(22) - 10(24) cm(-2)) AGNs is estimated to be approximate to 0.35 for luminosities L-X(2-10 keV) > 10(44) erg s(-1), independent of redshift. For less luminous sources, the fraction of obscured Compton-thin AGNs increases from 0.45 +/- 0.10 at z = 0.25 to 0.75 +/- 0.05 at z = 1.25. Studies that select AGNs in the infrared via template fits to the observed spectral energy distribution of extragalactic sources estimate space densities at high accretion luminosities consistent with the XMM-XXL constraints. There is no evidence for a large population of AGNs (e.g. heavily obscured) identified in the infrared and missed at X-ray wavelengths. We further explore the mid-infrared colours of XMM-XXL AGNs as a function of accretion luminosity, column density and redshift. The fraction of XMM-XXL sources that lie within the mid-infrared colour wedges defined in the literature to select AGNs is primarily a function of redshift. This fraction increases from about 20-30 per cent at z = 0.25 to about 50-70 per cent at z = 1.5.

The quasar 3C 279 was the target of an extensive multiwavelength monitoring campaign from 2006 January through April. An optical-IR-radio monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration was organized around target-of-opportunity X-ray and soft γ-ray observations with Chandra and INTEGRAL in 2006 mid-January, with additional X-ray coverage by RXTE and Swift XRT. In this paper we focus on the results of the WEBT campaign. The source exhibited substantial variability of optical flux and spectral shape, with a characteristic timescale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each other, while there was no obvious correlation between the optical and radio variability. After the ToO trigger, the optical flux underwent a remarkably clean quasi-exponential decay by about 1 mag, with a decay timescale of T d ∼ 12.8 days. In intriguing contrast to other (in particular, BL Lac type) blazars, we find a lag of shorter wavelength behind longer wavelength variability throughout the RVB wavelength ranges, with a time delay increasing with increasing frequency. Spectral hardening during flares appears delayed with respect to a rising optical flux. This, in combination with the very steep IR-optical continuum spectral index of α0 ∼ 1.5-2.0, may indicate a highly oblique magnetic field configuration near the base of the jet, leading to inefficient particle acceleration and a very steep electron injection spectrum. An alternative explanation through a slow (timescale of several days) acceleration mechanism would require an unusually low magnetic field of B ≲ 0.2 G, about an order of magnitude lower than inferred from previous analyses of simultaneous SEDs of 3C 279 and other flat-spectrum radio quasars with similar properties.

Context.M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 109 M⊙, whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz–10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intra-cluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radio-spectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of ≃10 μG, which increases to ≃13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of ≃40 Myr, which in turn provides a jet kinetic power of 6−10 × 1044 erg s-1.

L’objectif de ma thèse porte sur les interactions entre les noyaux actifs de galaxies et le milieu interstellaire des galaxies. En particulier, je mets l’accent sur les deux mécanismes possibles responsables de la production des vents par les trous noirs : les jets et les vents produits par le rayonnement de ces trous noirs. Les simulations hydrodynamiques de haute résolution des galaxies comprenant la rétroac- tion d’un jet ont montré que l’activité des noyaux actifs peut conduire à une pression exces- sive sur les régions denses de formation stellaire dans les galaxies, et donc à augmenter la formation d’étoiles, conduisant à un effet positif de rétroaction. Je montre que ces noyaux actifs induits par pression régulée et formation d’étoiles peuvent aussi être une explica- tion possible des taux de formation stellaire élevés observés dans l’Univers à haut décalage spectral. De plus, j’ai également étudié en détails comment le rayonnement émis à partir d’un disque d’accrétion autour du trou noir agit efficacement avec le milieu interstellaire et entraîne un fort vent galactique, en simulant la propagation des photons à partir des équations hydrodynamiques du rayonnement. Les simulations montrent que la grande luminosité d’un quasar est en effet capable de conduire des vents à grande échelle et à grande vitesse. Le rayonnement infrarouge est nécessaire pour transérer efficacement le gaz par multi-diffusion sur la poussière dans les nuages denses. Le nombre typique de multi-diffusion diminue rapidement quand le nuage central de gaz central se dilate et se rompt, ce qui permet au rayonnement de s’échapper à travers les canaux à faible densité. / Supermassive black holes (SMBHs) are known to reside in the centres of most large galaxies. The masses of these SMBHs are known to correlate with large-scale properties of the host galaxy suggesting that the growth of the BHs and large-scale structures are tightly linked. A natural explanation for the observed correlation is to invoke a self-regulated mechanism involving feedback from Active Galactic Nuclei (AGN). The focus of this thesis is on the interactions between AGN outflows and the ISM and how the feedback impacts the host galaxy. In particular, it focuses on the two possible mechanism of outflows, namely, outflows related to AGN jets and outflows produced by AGN radiation. High resolution, galaxy scale hydrodynamical simulations of jet-driven feedback have shown that AGN activity can over-pressurise dense star-formation regions of galaxies and thus enhance star formation, leading to a positive feedback effect. I propose, that such AGN-induced pressure-regulated star formation may also be a possible explanation of the high star formation rates recently found in the high-redshift Universe. In order to study in more detail the effects of over-pressurisation of the galaxy, I have performed a large set of isolated disc simulations with varying gas-richness in the galaxy. I found that even moderate levels of over-pressurisation of the galaxy boosts the global star formation rate by an order of magnitude. Additionally, stable discs turn unstable which leads to significant fragmentation of the gas content of the galaxy, similar to what is observed in high-redshift galaxies. The observed increase in the star formation rate of the galaxy is in line with theoretical predictions. I have also studied in detail how radiation emitted from a thin accretion disc surrounding the BH effectively couples to the surrounding ISM and drives a large scale wind. Quasar activity is typically triggered by extreme episodes of gas accretion onto the SMBH, in particular in high-redshift galaxies. The photons emitted by a quasar eventually couple to the gas and drive large scale winds. In most hydrodynamical simulations, quasar feedback is approximated as a local thermal energy deposit within a few resolution elements, where the efficiency of the coupling between radiation of the gas is represented by a single parameter tuned to match global observations. In reality, this parameter conceals various physical processes that are not yet fully un- derstood as they rely on a number of assumptions about, for instance, the absorption of photons, mean free paths, optical depths, and shielding. To study the coupling between the photons and the gas I simulated the photon propagation using radiation-hydrodynamical equations (RHD), which describe the emission, absorption and propagation of photons with the gas and dust. Such an approach is critical for a better understanding of the coupling between the radiation and gas and how hydrodynamical sub-grid models can be improved in light of these results...