No description available.

No description available.

My thesis project consisted in the data reduction and analysis of a set of Ks-band data. The near-infrared (NIR) observations were performed in the context of XMM-LSS, an X-ray survey with the main goal of studying the Large Scale Structures (LSS) of the Universe using ESA's satellite XMM--Newton. Multi-wavelength observations, coming from Legacy surveys associated to XMM-LSS, allowed not only to perform a detailed study of the properties of the selected population but also understand in-depth the selection process followed.

Clusters of galaxies are host to powerful Active Galactic Nuclei (AGN) that greatly affect the thermal history of clusters. By keeping X-ray emitting gas from cooling, massive, run away star formation does not occur in the brightest cluster galaxy (BCG). This is achieved through radio jets displacing large quantities of metal-rich gas and carving out cavities in the intracluster medium (ICM). This metal-rich gas was originally formed within the BCG and ejected through type Ia supernovae. The current distribution of the ejecta suggests an extra source of energy has spread the material far out into the ICM. Currently, it is unclear what mechanisms are responsible. In this thesis, I present evidence, in the form of X-ray imaging and spectra, that establishes a link between AGN and the observed distribution of metal-rich gas. First, the BCG in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~23 solar masses per year. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5×10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. (2008) to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile. Next, using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the ICM is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ~120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2E7 and 7E7 solar masses which represents 10% - 30% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the AGN. Evidently, Hydra A’s powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment timescale < 1E9 yr implies that the metals lost from the central galaxy will be quickly replenished. Finally, we present an analysis of the spatial distribution of metal-rich gas in 29 galaxy clusters using deep observations from the Chandra X-ray Observatory. The BCGs have experienced recent active galactic nucleus activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the BCG into the ICM along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R ~ P^0.43, with a scatter of only 0.42 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting this is a long lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal enriched gas beyond 1 Mpc unless their masses substantially exceed 1E9 solar masses. It is likely however for these black holes to output enough energy to uplift all the peaked, metal-rich gas beyond the BCG to the currently observed widespread distribution.

Clusters of galaxies are host to powerful Active Galactic Nuclei (AGN) that greatly affect the thermal history of clusters. By keeping X-ray emitting gas from cooling, massive, run away star formation does not occur in the brightest cluster galaxy (BCG). This is achieved through radio jets displacing large quantities of metal-rich gas and carving out cavities in the intracluster medium (ICM). This metal-rich gas was originally formed within the BCG and ejected through type Ia supernovae. The current distribution of the ejecta suggests an extra source of energy has spread the material far out into the ICM. Currently, it is unclear what mechanisms are responsible. In this thesis, I present evidence, in the form of X-ray imaging and spectra, that establishes a link between AGN and the observed distribution of metal-rich gas. First, the BCG in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~23 solar masses per year. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5×10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. (2008) to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile. Next, using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the ICM is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ~120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2E7 and 7E7 solar masses which represents 10% - 30% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the AGN. Evidently, Hydra A’s powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment timescale < 1E9 yr implies that the metals lost from the central galaxy will be quickly replenished. Finally, we present an analysis of the spatial distribution of metal-rich gas in 29 galaxy clusters using deep observations from the Chandra X-ray Observatory. The BCGs have experienced recent active galactic nucleus activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the BCG into the ICM along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R ~ P^0.43, with a scatter of only 0.42 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting this is a long lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal enriched gas beyond 1 Mpc unless their masses substantially exceed 1E9 solar masses. It is likely however for these black holes to output enough energy to uplift all the peaked, metal-rich gas beyond the BCG to the currently observed widespread distribution.

All active galactic nuclei (AGN) are known to vary in the rest-frame UV/optical. Typical variations are on the order of 30% or so and are stochastic in nature. Therefore, the discovery of a number of extreme AGN transients, which are smoothly evolving on year-long timescales and by a factor of four or more, is surprising and necessitates further analysis. Are these objects simply at the extreme end of the variability distribution seen in normal quasars or is there another mechanism which can explain their atypical behaviour? The primary focus for this work is on the possibility that a number of these extreme AGN transients are actually rare, high-amplitude microlensing events, caused by intervening stellar mass object(s). Not only do the microlensing models provide an explanation for the observed variability but they also allow constraints to be placed on the morphology of the emitting regions of the AGN, namely the accretion disc and broad line region (BLR). These transients have been monitored both photometrically and spectroscopically, since their discovery. The majority of spectroscopic observations have been conducted using the William Herschel Telescope. At time of writing (Sept. 2017), there are now 64 confirmed AGN and 235 individual spectra. The spectral reduction pipeline, calibration and initial measurements are described in Chapter 2. This chapter also details the microlensing models and procedures used in interpreting both the light curve information and spectral measurements. This includes: a comprehensive treatment of the simple point-source/point-lens model; quantitative point-lens models which allow for the use of extended sources; and also an initial exploration into more complex lensing morphologies involving multiple lensing objects and/or an external shear. Chapter 3 details the results of the spectroscopic monitoring campaign for the entire transient sample. A general classification scheme is developed which allows for a comparison of the evolutionary trends seen in objects exhibiting similar behaviour. A subset of transient AGN, the most extreme objects in the sample, is also discussed in detail, with a particular focus on the evolution of the continuum, line fluxes and equivalent widths. Chapter 4 details the results of the analysis of four key targets, selected for their suitability in addressing the microlensing hypothesis. For two targets the point-source point-lens model performs very well. Lens parameters for these objects are presented and in one particular case, the data is sufficient to allow constraints to be placed on the size of various components comprising the broad line region. Chapter 5 expands the microlensing analysis to include the entire AGN transient sample. Approximately 10% of objects are well matched by a simple point-source, point-lens microlensing model. In other objects, evidence is seen which requires a more complex lensing scenario to adequately explain. In one class of objects there is also evidence that the accretion disc is being resolved by the lens. Chapter 6 revisits a notable are seen in an AGN which lies behind M31. The analysis reaffirms that this event is well described by a simple microlensing model and provides an independent estimate that the most probable location for the lens is within M31 itself.

We organized an international campaign to observe the blazar 0716+714 in the optical band. The observations took place from February 24, 2009 to February 26, 2009. The global campaign was carried out by observers from more that sixteen countries and resulted in an extended light curve nearly seventy-eight hours long. The analysis and the modeling of this light curve form the main work of this dissertation project. In the first part of this work, we present the time series and noise analyses of the data. The time series analysis utilizes discrete Fourier transform and wavelet analysis routines to search for periods in the light curve. We then present results of the noise analysis which is based on the idea that each microvariability curve is the realization of the same underlying stochastic noise processes in the blazar jet. Neither reoccuring periods nor random noise can successfully explain the observed optical fluctuations. Hence in the second part, we propose and develop a new model to account for the microvariability we see in blazar 0716+714. We propose that the microvariability is due to the emission from turbulent regions in the jet that are energized by the passage of relativistic shocks. Emission from each turbulent cell forms a pulse of emission, and when convolved with other pulses, yields the observed light curve. We use the model to obtain estimates of the physical parameters of the emission regions in the jet.

No description available.

We have observed two high -redshift quasars with the echelle spectrograph and 2D- Frutti Photon Counter at Las Campanas, in order to investigate the statistical properties of the Lyman -a forest. The two-point correlation function for the Lyman -a forest lines at z .^s 3 is consistent with zero, for all velocity splittings A > 50 km /sec. When Lyman -a lines and other metal lines from known metalline systems are included, the correlation function shows a weak non -zero signal at small A . We suggest that the weak clustering of the Lyman -a forest detected by other workers may be the result of contamination by a small number of metal -line systems and their associated Lyman -a lines.

We combine optical, X-ray (Einstein and ROSAT) and infrared (IRAS) data to investigate the evolution and spatial distribution of AGN with particular emphasis on the implications for the origin of the diffuse X-ray background. First, we derive the IRAS Seyfert luminosity function to test the continuity of properties between the Seyfert and the QSO population. The QSO luminosity function evolved back to z ~ 0, agrees well with the Seyfert luminosity function. In particular, the similarity of the faint parts of the two luminosity functions, suggests that the optical luminosity function is not severely affected by incompleteness due to reddening. We analyze the clustering properties of the IRAS Seyfert sample in order to probe the AGN clustering evolution. We detect clear clustering (5σ) at scales < 20 h(^-1). Comparing the Seyfert with the QSO clustering results at higher redshifts we find that a comoving model for AGN clustering evolution, where AGN clusters are expanding with the Hubble flow, is probably favoured by the data. Using new faint CCD observations we recalibrate the photometry of the Durham UVX catalogue of Boyle et al. (1990). We show that the luminosity function 'knee' feature claimed by Boyle et al. is not an artefact of photometric errors at faint magnitudes. We evaluate the contribution of Active Galactic Nuclei (AGN) to the X-ray background using this optical luminosity function and evolve it according to Pure Luminosity Evolution models. We estimate that AGN produce around half of the X-ray background at 2 keV. This contribution is consistent with the small scale (arcmin) fluctuations of the X-ray background for both the stable and comoving model of clustering evolution. If a large number of low luminosity AGN with high intrinsic absorption is missed by the optical surveys, AGN could produce all the 2 keV intensity. Although the uncertainty in the estimate of the AGN contribution is high, this work demonstrates, at least, that Pure Luminosity Evolution models are consistent with both the X-ray background intensity and anisotropy constraints. A recent deep ROSAT observation yields a high surface density of X-ray sources (> 100 deg(^-2). Spectroscopic follow up observations show that most of these sources are QSOs. The identified QSOs contribute ~ 30% at 1 keV and therefore this is the lower limit of the AGN contribution to the X-ray background. No other class of sources contributing substantially to the X-ray background has been yet identified.