This thesis is an investigation into the emission from an individual Narrow Line Seyfert 1 (NLS1) Active Galactic Nuclei (AGN) NGC 4051. NLS1s have all the properties of Seyfert galaxies but show peculiar characteristics, including the narrowest Balmer lines, strongest Fe II emission and extreme properties in the X-rays. NGC 4051, is one of the most X-ray bright Seyferts and it has been studied extensively by a number of X-ray observatories. Recent studies have also revealed that Seyfert cores are variable at radio wavelengths, however, there are very few Seyfert radio variability investigations, and this is one of the first that also investigates the radio/X-ray (jet/disc) coupling. It has been known for some time that both the X-ray and continuum radio observations provide an optimal tool to access the innermost regions of the AGN. A combination of X-ray, radio and optical data is used here to give an in depth analysis of both the core and extended emission regions of NLS1 NGC 4051. This work reveals that there is no clear evidence for radio variability in the core emission of NGC 4051 at 8.4 GHz with the possible exception of very low amplitude » 0.12 mJy variations detected in VLA A configuration. Deep VLA observations reveal a mean spectral index value of a » −0.3 for the core, suggesting a self absorbed jet. The surrounding radio emission has steeper spectral index values in the range of −0.5 < a < −1.6 which suggests the extended radio emission is optically thin synchrotron emission. During the A configuration observations both VLA radio data sets (2000-2001 and 2008-2009) reveal a very weak positive correlation between the radio and much larger amplitude X-ray variations but there is no evidence for a b value much greater than » 0.1 for the LR µ LbX relationship, which is consistent with a constant radio luminosity for the core. Collimated VLBI structure is detected which hints at the presence of an unseen jet. The proposed jet is of non-negligible power and estimates of the buoyancy speed of the lobes, and the break timescales from the radio spectral index provide evidence for radio activity in NGC 4051 occurring on timescales greater than > 106 years. Also, a change in the relative distance of the SW hotspot with respect to the core (seen in VLBI images) gives an apparent jet velocity 0.012 pc yr−1, equivalent to a speed of 11,700 kms−1 (» 0.04 c). Deep VLA radio imaging of NGC 4051 shows double lobed radio emission, which lies along the same PA as optical [OIII] emission. The nucleus of the [OIII] emission is coincident with the core radio emission. This structure suggests the presence of a double sided ionisation cone, where both radio and optical emission are collimated by the same disc or tori.

In the last two decades astronomers carried out a large number of galaxy surveys tuned towards the study of galaxy formation and evolution. With the ever improving technology, increasing telescope sizes of ground-based telescopes and the development of space-based telescopes it has become possible to detect galaxies at a time when the Universe was only a few hundred million years old. However, for the majority of galaxies a detailed spectroscopic analysis is not possible due to their distance and limited telescope time. Thus, many surveys rely on photometric data alone to help unveil the properties of galaxies. One of the most important areas of study within galaxy formation and evolution is the analysis of the galaxy stellar population parameters as these can provide us with information about the star formation histories of galaxies and when and possibly how they assembled their mass. A popular approach in the literature is the fitting of synthetic spectral energy distributions inferred from stellar population modelling to the multi-wavelength photometry of galaxies. However, this approach comes with a large number of fitting parameters all of which are essentially user-dependent and will bias the result in one way or another. The aim of this thesis is to investigate the accuracy and efficiency of spectral energy distribution fitting as derivation technique for the galaxy physical properties, such as age, stellar mass, dust reddening, etc., as a function of the fitting parameters, such as star formation histories, age grids, metallicity, initial mass function, dust reddening, reddening law, filter setup and wavelength coverage and stellar population model, and to find the setup of parameters that recovers the properties best. In particular, we investigate in detail the dependence of the derived properties on the assumed wavelength coverage and exact filter setups. Mock galaxies with known properties serve as test particles for this exercise. The synthetic spectral energy distributions used in this thesis are based on the Maraston (2005) stellar population models. Literature results which investigate similar problems are obtained using the models of Bruzual & Charlot (2003). Firstly, the fitting is carried out under the assumption that galaxy redshifts are known mimicking surveys for which galaxy redshifts are derived spectroscopically. Then we study the case in which the redshift is not known and needs to be determined alongside the galaxy physical properties which is the case for most photometric surveys. In general, we find that - using normal template star formation histories as widely used in the literature - ages and stellar masses of star-forming galaxies are underestimated, reddening and star formation rates are overestimated. This is due to a mismatch in star formation history and the overshining effect. The addition of the rest-frame near-IR appears to be crucial for the derivation of robust results. For aged galaxies with little or no on-going star formation we find that a setup covering a wide range of star formation histories and metallicities works best when the fit is carried out excluding dust reddening. For high redshift star-forming galaxies we find that a new type of star formation history (inverted-� models which start forming stars at high redshift) recovers stellar masses and star formation rates best. The parameters of truly passive galaxies are much better determined. In order to ease the comparison of literature data that was analysed with different fitting parameter setups we provide scaling relations for the transformation of stellar masses between different setups. Our results concerning the importance of the wavelength coverage in the fitting are particularly useful for the planning of future surveys and observation proposals. We apply our findings from the study of mock galaxies to various samples of real galaxies which cover different redshift ranges and galaxy types. We derive the stellar population properties for a sample of star-forming galaxies at z ∼ 2 from the GOODS-S survey using inverted-� models (with high formation redshifts) and show that the obtained dust reddening and star formation histories are in excellent agreement with those derived from other methods. We also show how the wrong set of fitting parameters can lead to unrealistically young ages, low stellar masses and high star formation rates which are a pure artefact from the fit. Furthermore, we study a sample of low redshift, predominantly passive galaxies from the SDSS-III/BOSS survey for which we use the spectral model of Maraston et al. (2009) that is tuned to the needs of this particular type of galaxies. We find that BOSS galaxies are mostly passive, old and massive at each redshift in the range 0 < z < 0.7. Finally, we complement the study of SDSS-III/BOSS galaxies by deriving stellar masses for the SDSS-I/II galaxies in a similar fashion. We conclude that the simultaneous derivation of stellar population properties of galaxies from spectral energy distribution fitting is difficult but that these properties can be very well derived provided the right setup and wavelength coverage are used in the fitting. We also conclude that more work is needed to better match star formation histories of aged galaxies with little on-going star formation in order to improve estimates of stellar population parameters.

This Thesis contains two parts. Part I details my work on KMOS, a new instrument for the VLT and Part II details my research on scaling relations for the massive galaxy cluster MS0451.6-0305. Part I: The K-Band Multi-Object Spectrograph (KMOS) is a new near infra-red (NIR) instru- ment to be installed at the Very Large Telescope (VLT). KMOS is capable of spatially resolved kinematics via 24 deployable integral field units (IFUs), each with a 2.8′′ field of view. I describe my contribution to the construction and optical characterisation of the spectrograph modules and instrument as a whole. Part II: GMOS-N spectroscopy has been used to obtain velocity dispersions (σ) and archival HST photometry has been used to determine the effective radii (Re) & average surface brightnesses within Re (⟨I⟩e) of 26 confirmed cluster members of MS0451.6-0305 at z = 0.55. The Kormendy Relation, Faber-Jackson Relation and Fundamental Plane have been produced for the cluster and have been compared to the results for a local reference sample in Coma. GMOS-N g′ and r′ band photometry has also been used to produce a Colour-Magnitude Relation for MS0451.6-0305. It is found that the KR and FJR disagree at the 2.1σ level with respect to luminosity evolution since z = 0.55. When correcting for size-evolution (SE), the magnitude offsets agree and are consistent with passive evolution of the galaxy stellar populations from a single burst of star formation 9.8+4.5-1.7 Gyrs ago or z = 1.7+∞-0.6. The median offset in the FP relation for the SE corrected data is also consistent with this formation epoch. Evidence is found for the evolution of the FP tilt in MS0451.6-0305, where it is shown to be steeper than that of the Coma FP, when expressed as a relation between galaxy mass and M/L.

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The known population of high-mass X-ray binaries in the Small Magellanic Cloud is continually growing and is now a similar size to that of the Milky Way, despite a significant mass difference between the two galaxies. In this thesis, I present multi-wavelength observations of Be/X-ray binaries that have undergone an outburst during the past three years, including the discovery of new systems and extended outbursts from previously known sources. The results are discussed in terms of both the underlying physics of individual outbursts and how the growing SMC population is helping our understanding of the formation and evolution of highmass X-ray binaries. In particular, I describe the orbital analysis of every extended X-ray outburst detected by the Rossi X-ray Timing Explorer and present the first significant sample of systems outside of the Milky Way for which a binary orbital solution is known.

Les molécules organiques complexes sont abondantes dans le milieu interstellaire et leur détection est indispensable à la compréhension des processus chimiques gouvernant l'univers. Les détections astronomiques sont réalisées par des télescopes comme ALMA, SOFIA, HERSCHEL et IRAM, dans le domaine millimétrique. À cette fin la spectroscopie de rotation en laboratoire est une étape indispensable. L'étude du glycolaldéhyde, de l'isocyanure d'allyle et du formiate de méthyle a été réalisée. Les spectres ont été enregistrés sur le spectromètre millimétrique et submillimétrique du PhLAM. Le glycolaldéhyde est une molécule pré-biotique possible, les états fondamentaux et les trois premiers modes de vibration des deux isotopologues 13C ont été modélisés par le modèle théorique du Hamiltonien de Watson. Le formiate de méthyle, isomère du glycolaldéhyde, est très abondant dans le milieu interstellaire. Il contient un groupe méthyle et est caractérisé par un mouvement de grande amplitude qui se couple avec la rotation globale de la molécule. La modélisation de ce couplage a nécessité un ajustement global des états de torsion νt = 0 et 1 du groupe méthyle de l'isotopologue 13C-2. Sa détection dans Orion-KL sera reportée. L'isocyanure d'allyle est d'intérêt astrophysique. Cette molécule présente une structure hyperfine due à l'atome N et résolue uniquement dans le domaine micro-onde. L'analyse des états fondamentaux des conformères Cis et Gauche les plus stables a été entendue dans le domaine millimétrique et submillimétrique. L'interaction de Coriolis (type a et b) entre les niveaux ν1 = 1 et ν2 = 1 du conformère Cis de l’isocyanure d’allyle a été modélisée. / Complex organic molecules are abundant in the interstellar medium and their detection play a big role in the comprehension of the chemical processes governing the evolution of the universe. Astronomical detection in the millimeter- wave region is realized by the use of telescopes such as ALMA, SOFIA, HERSCHEL and IRAM. For this purpose, rotational spectroscopy in the laboratory is an essential stage. In consequence, the study of glycolaldehyde, allylisocyanide and methylformate was elaborated. The spectrum of these molecules was recorded with the millimeter- and submillimeter- wave spectrometer in the PhLAM laboratory. Glycolaldehyde is a possible prebiotic molecule. The rotational spectra of the ground state and the three lowest vibrational modes for the two 13C isotopologs were modeled by a Watson Hamiltonian. The methylformate is an isomer of glycolaldehyde and is very abundant in the interstellar medium. It is characterized by the presence of methyl group establishing large amplitude motion witch couples with the global rotation of the molecule. To model this interaction for the 13C-2 isotopolog, a global fit of the two torsional states νt = 0 et 1 of the methyl group is required. The detection of νt = 1 in Orion-KL will be reported. Allylisocyanide is of astrophysical interest. This molecule establishes an hyperfine structure due to the presence of the N atom. This structure is resolved only in the micro- wave domain. The analysis of the ground state of both conformers was extended in the millimeter- and submillimeter- wave regions. Coriolis interactions of a and b types between ν1 = 1 and ν2 = 1 sates of the Cis conformer was resolved.

We present a multi-wavelength analysis of IRAS FSC10214+4724 from radio to X-ray wavelengths. This is a gravitationally lensed galaxy at a redshift z=2.3 (3 Gyr after the Big Bang) which hosts prodigious star formation as well as an obscured active nucleus. We derive a new lens model for the system employing a Bayesian Markov Chain Monte Carlo algorithm with extended-source, forward ray-tracing. An array of spatially resolved maps (radio, millimetre, near-infrared, optical) trace different physical components which enables a high resolution, multi-wavelength view of a high-redshift galaxy beyond the capabilities of current telescopes. The spatially-resolved molecular gas total intensity and velocity maps reveal a reasonably ordered system, however there is evidence for minor merger activity. We show evidence for an extended, low-excitation gas reservoir that either contains roughly half the total gas mass or has a different CO-to-H_2 conversion ratio. Very Long Baseline Interferometry (VLBI) is used to detect what we argue to be the obscured active nucleus with an effective angular resolution of <50 pc at z=2.3. The source plane inversion places the VLBI detection to within milli-arcseconds of the modeled cusp caustic, resulting in a very large magnification (mu > 70) which is over an order of magnitude larger than the derived co magnification. This implies an equivalent magnification difference between the starburst and AGN components, yielding significant distortion to the global continuum spectral energy distribution (SED). A primary result of this work is therefore the demonstration that emission regions of differing size and position within a galaxy can experience significantly different magnification factors (> 1 dex) and therefore distort our view of high-redshift, gravitationally lensed sources. This not only raises caution against unsophisticated uses of IRAS FSC10214+4724 as an archetype high-redshift Ultra-Luminous Infra-Red Galaxy (ULIRG), but also against statistical deductions based on samples of strong lenses with poorly constrained lens models and spatially-unresolved detections. Analogous to the continuum SED distortion quantified in this thesis, we predict a distortion of the CO spectral line energy distribution of IRAS FSC10214+4724 where higher order J lines, that are increasingly excited by the AGN and shock heating from the central starburst, will be preferentially lensed owing to their smaller solid angles and closer proximity to the AGN, and therefore the cusp of the caustic. This distortion is predicted to affect many high redshift lenses and will be tested most synergistically by the Jansky Very Large Array (JVLA) and the Atacama Large Millimetre Telescope (ALMA).

In this thesis I present new interferometric ¹²CO observations of 30 early-type galaxies (ETGs). These galaxies were the brightest ~2/3 of CO detected ETGs from the complete, volume limited Atlas^3D survey. By including literature data I construct the largest ever sample of mapped ETGs, containing 41 objects, and use this sample to analyse the morphology, kinematics and origin of the molecular gas. Many of the galaxies in this sample have relaxed molecular discs, but polar structures, rings, bars and disturbed gas distributions are also present. Around half of the galaxies have molecular gas that follows the stellar light profile, similar to molecular gas in spirals, while others have molecular gas excesses, truncations, rings or composite profiles. The molecular gas extent is smaller in absolute terms in ETGs than in late-type galaxies, but the size distributions are similar once scaled by the galaxies optical/stellar characteristic scalelengths. Cluster environments, however, lead to systems having denser, more compact molecular reservoirs. I find that molecular gas is an excellent kinematic tracer, even in high-mass ETGs, and thus molecules may be the kinematic tracer of choice for probing the M/L evolution of galaxies over cosmic-time. I use this knowledge to construct the first ever early-type CO Tully-Fisher relation, and show that it is offset from the Tully-Fisher relation of spirals by 0.98±0.22 magnitudes at Ks-band. I find that a third of my sample galaxies have their molecular and ionised gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). The origin of the molecular gas seems to depend strongly on environment, with externally acquired material being common in the field but nearly completely absent in Virgo. Furthermore, my results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample always having kinematically aligned gas.

Περίπου το 70% των αστέρων που παρατηρούνται στο σύμπαν είναι μέλη πολλαπλών συστημάτων και η μελέτη τους είναι υψίστης σημασίας για τους αστρονόμους τις τελευταίες δεκαετίες. Τα διπλά εκλειπτικά συστήματα προσφέρουν μοναδικές δυνατότητες μελέτης των αστρικών παραμέτρων και κατ’ επέκταση των θεωριών εξέλιξης εξαιτίας της γεωμετρίας τους και αποτελούν τη βάση της μεθόδου προσδιορισμού αστρονομικών αποστάσεων ως «πρότυπα κεριά» (standard candles). Στην παρούσα εργασία πραγματοποιείται η μοντελοποίηση των καμπυλών φωτός 36 λαμπρών αποχωρισμένων διπλών εκλειπτικών συστημάτων που παρατηρήθηκαν κατά την τρίτη φάση του προγράμματος OGLE στο Μεγάλο Νέφος του Μαγγελάνου και εξάγονται οι φωτομετρικές τους παράμετροι, ώστε τα πιο ενδιαφέροντα από αυτά να επιλεχθούν για περαιτέρω φασματοσκοπικές παρατηρήσεις ως υποψήφιοι δείκτες απόστασης. Στο πρώτο κεφάλαιο πραγματοποιείται μία εισαγωγή στους μεταβλητούς αστέρες, μία αναφορά στην ταξινόμηση των διπλών εκλειπτικών συστημάτων σύμφωνα με το μοντέλο Roche και με τη μορφή της καμπύλης φωτός τους καθώς και στοιχεία που αφορούν τη γεωμετρία τους και τις εξισώσεις της τροχιάς τους. Στο δεύτερο κεφάλαιο περιγράφεται το πρόγραμμα OGLE (Optical Gravitational Lensing Experiment) σκοπός του οποίου είναι η ανίχνευση συμβάντων βαρυτικής μικροεστίασης με κύριους στόχους τα Νέφη του Μαγγελάνου, το Γαλαξιακό Δίσκο και την Κεντρική Περιοχή του Γαλαξία. Ως αποτέλεσμα της χαρτογράφησης των πεδίων αυτών είναι η δημιουργία μίας μεγάλης βάσης δεδομένων μεταβλητών αστέρων για περεταίρω μελέτη. Στο τρίτο κεφάλαιο περιγράφεται αναλυτικά το πρόγραμμα PHOEBE (PHysics Of Eclipsing BinariEs) με το οποίο πραγματοποιήθηκε η μελέτη των καμπυλών φωτός των 36 συστημάτων. Το πρόγραμμα αυτό αποτελεί μία βελτιωμένη έκδοση του προγράμματος WD (Wilson & Devinney 1979) που στηρίζεται στη μέθοδο των διαφορικών διορθώσεων για της εξαγωγή των φωτομετρικών παραμέτρων των συστημάτων. Τέλος στο τέταρτο κεφάλαιο παρουσιάζεται η μέθοδος επιλογής των 36 διπλών εκλειπτικών συστημάτων που μελετήθηκαν, ο προσδιορισμός των βασικών παραμέτρων που εισήχθησαν στο πρόγραμμα, οι φωτομετρικές παράμετροι που διεξήχθησαν καθώς και τα επιστημονικά συμπεράσματα της μελέτης. / Over 70% of the stars in the universe are components of multiple systems. The study of these systems is crucial for the astronomers over the last decades because their parameters can be derived due to their geometry and assumptions can be made about stellar evolution. Moreover these systems are very promising for measuring distances in the universe as “standard candles”. In the present work 36 DEBs were chosen from the third phase of OGLE program from the Large Magellanic Cloud and Light Curve modeling was held via PHOEBE program which is an improved version of WD code (Wilson & Devinney 1979). Photometric parameters of these systems were derived so that the most interesting of these would be potential targets for further spectroscopic observations as distance indicators for the Large Magellanic Cloud.

Στόχος της παρούσης εργασίας είναι η διερεύνηση των μεταβολών της ροής της οπτικής ακτινοβολίας στα φίλτρα B, V, R στη διάρκεια μιας νύχτας του ενεργού γαλαξία S5 1803 + 784 με ανάλυση παρατηρήσεων που ελήφθησαν με το τηλεσκόπιο των1.3m του αστεροσκοπείου του Πανεπιστημίου Κρήτης (από τον Δρ. Παν. Μπούμη) με τη μέθοδο της συγκριτικής φωτομετρίας. Στο πρώτο κεφάλαιο περιγράφονται τα γενικά χαρακτηριστικά των κανονικών γαλαξιών και του δικού μας γαλαξία, ενώ στο δεύτερο τα γενικά χαρακτηριστικά των ενεργών γαλαξιών ή ενεργών γαλαξιακών πυρήνων (AGN) - επειδή τα έντονα ενεργητικά φαινόμενα επικεντρώνονται στην κεντρική περιοχή του πυρήνα. Αναφέρεται η διάκρισή τους σε κατηγορίες με βάση τα παρατηρησιακά χαρακτηριστικά και εξετάζονται οι βασικές ιδέες που οδηγούν στο επικρατέστερο μοντέλο ενοποίησης, σχετικά με την ενεργειακή μηχανή τους καθώς και η εξέλιξη και τροποποίηση του με βάση τα νέα πειραματικά δεδομένα. Το τρίτο κεφάλαιο επικεντρώνεται στα ιδιαίτερα χαρακτηριστικά των blazars στα οποία ανήκει ο S5 1803 + 784. Στο τέταρτο κεφάλαιο περιγράφονται συνοπτικά οι βασικές αρχές της φωτομετρίας αλλά και οι βασικές παράμετροι μιας CCD κάμερας. Στο τέταρτο κεφάλαιο γίνεται μια βιβλιογραφική παρουσίαση του S5 1803 +784 σε όλα τα μέρη του φάσματος και περιγράφονται αναλυτικά οι παρατηρήσεις, τα αρχικά στάδια επεξεργασίας των αστρονομικών εικόνων και τα αναλυτικά στάδια της φωτομετρίας του γαλαξία με τις απαραίτητες διορθώσεις. Τέλος στο έκτο κεφάλαιο κατασκευάζονται οι καμπύλες μεταβολής της ροής και σχολιάζονται τα αποτελέσματα Ακολουθεί στο παράρτημα, η περιγραφή των προγραμμάτων και των διαδικασιών που χρησιμοποιήθηκαν τόσο στην ανάλυση όσο και στην φωτομετρία μέσω των αστρονομικών πακέτων IRAF και MIDAS , ως μικρός οδηγός για τους επόμενους ενδιαφερόμενους. / The main aim of this dissertation entitled “Variabillity in the optical band of blazar S51803+784” is the investigation of flux microvariability through observations carried out with the 1.3 m , Ritchey-Chretien telescope at Skinakas Observatory in Crete, Greece (by Associate Researcher P. Boomis of the Institute of Astronomy and Astrophysics of the National Observatory in Athens) in 2001 under the supervision of Lecturer Mrs E-P. Christopoulou (Physics Dept. University of Patras, Greece). This work consists of six relatively distinct chapters. The first chapter summarizes the main characteristics of normal galaxies whereas the second one describes the various classes of Active Galactic Nuclei which emerge from multiwavelength studies and the unified model proposed to explain the energy source behind their taxonomy. The last section of this part focuses on the observational evidence of supermassive black holes. The third chapter focuses on the special characteristics of the class named Blazars, the proposed theoretical models for the formation of jets and the observed microvariability thought the EM spectrum. The fourth chapter describes the main philosophy of photometry, the comparison of differential and absolute photometry and the selection of photometric standard stars. The last part briefly presents the charge-coupled devices (CCDs) which are used to record astronomical images and their main properties. The fifth chapter deals with the current observations of the Blazar S51803+784 and the standard image processing (bias substraction and flat fielding using twilight –sky exposures) applied to all frames before the performance of aperture photometry techniques which is described analytically in the rest part. The topics covered include methods for image center determination, routines for estimating the sky background and the techniques of both aperture and point-spread function fitting photometry. Procedures for transforming instrumental magnitudes to those on a standard system are also discussed. The results based on the data reduction of the photometric observations of the object are presented in the last chapter together with the discussion and conclusions. Finally in the Appendix there is a mini-guide for the beginner in order to be familiar with the format of the astronomical files, and the various astronomical packages and procedures being used for the above reduction.