The high-mass X-ray binary SMC X-1 has been observed during the interval 1986-1989 at a threshold γ-ray energy of 0.4 TeV using the University of Durham Mark III air Cerenkov telescope at Narrabri. The Cerenkov arrival time series recorded during these observations have been tested for periodicity at the contemporary pulse period of the SMC X-1 X-ray pulsar. This period analysis was performed using a new technique - introduced in the present work - which is designed for TeV γ-ray source candidates in binary systems and which simultaneously seeks evidence for pulsed TeV γ-ray emission and information on the location of the emission site within the binary. Results are also presented from the period analysis of data accumulated at Narrabri during observations of the low-mass X-ray binaries X0021.8-7221 (in the globular cluster 47 Tucanae) and GX 1+4. X-ray binaries as a class of TeV γ-ray source are considered and their properties compared. Previous models which invoke the interaction of beams of high-energy particles with material within the environment of a binary system are discussed. One of these models is adapted in the present work in order to propose a simple explanation of the narrow TeV 7-ray orbital light curve observed for the high-mass binary Centaurus X-3. The new model accounts for the γ-ray emission from Cen X-3 in terms of the collisions of ultrarelativistic protons with an accretion wake trailing the X-ray pulsar. This model, which incorporates the steering of charged particles in the magnetosphere of the massive primary star, is also applied to the Vela X-1 binary in order to investigate claims that TeV γ-ray outbursts observed during X-ray eclipse arise at particle collisions with the limb of the supergiant companion.

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.

Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references.

L'étude des propriétés résolues des galaxies lointaines peut apporter des connaissances fondamentales sur les processus qui gouvernent l'évolution des galaxies tout au long de la vie de l'Univers. Par exemple, ces études peuvent nous aider à mieux comprendre si une galaxie a fusionné avec une autre dans le passé, à tester de nouvelles hypothèses concernant la distribution de matière (noire et visible) dans les galaxies et aussi à étudier la densité et composition chimique du gaz. Pendant longtemps, ces études étaient coûteuses et assez peu efficaces (d'un point de vue observationel), vu qu'elles obligeaient à faire plusieurs observations discontinues du même objet. Mais dans les trois dernières décennies, grâce aux développements instrumentaux qu'on permis la construction d'une nouvelle classe de spectrographes -- les Spectrographes de champ Intégral -- il est finalement devenu relativement simple d'avoir une vraie vision tridimensionnelle des galaxies et de mesurer les variations spatiales de propriétés comme la cinématique, le taux de formation stellaire et la métallicité. Néanmoins, ces études résolues restent encore difficiles à faire pour des galaxies lointaines, que sont la plupart du temps très petites sur le ciel et très faibles. Une méthode qui peut aider à mener ces études est d'observer objets derrière des amas de galaxies. Les amas, à cause de leur masse très élevé, forment des lentilles gravitationnelles qui augmentent la brillance des objets derrière eux, fonctionnant comme un 'télescope cosmique'. L'effet peut aussi 'étendre' les objects dans le ciel, ce que permet d'analyser des échelles spatiales plus petites qu'en observant des galaxies non lentillées. Au cours de ma thèse, j'ai analysé les propriétés résolues de huit de ces objects très magnifiés par des amas de galaxies. Dans la première partie de ce manuscrit, je présente un ensemble de 7 arcs gravitationnels: des galaxies extrêmement étendues et magnifiées mais qui restent représentatives des galaxies typiques de ce temps cosmique, il y a 6 - 9 Gyr. Tout ces galaxies sont des disques en rotation avec des masses entre109 et 1011 M⊙ et taux de formation stellaires de 3 - 50 ⊙/yr. À partir de la émission [OII], les champs de vitesse et de dispersion de vitesse de ces 7 objets ont été mesurés, ce que nous a permis de conclure que toute ces galaxies sont dominées par rotation. En prenant en compte les effets de distorsion de lentille gravitationnelles, les meilleurs paramètres pour trois modèles différents -- le modèle arc tangente, sphère isotherme et disque exponentiel -- on été dérivés pour chaque galaxie. Je conclus que le modèle de sphère isotherme, qui suppose que la masse de la galaxie est dominée par la distribution de la matière noire, décrit marginalement mieux le champ de vitesse de 3 de ces 7 galaxies que les deux autres modèles. Dans la deuxième partie du manuscrit, une jeune galaxie à z=3.5, avec une masse de M* = 6 x 109 M⊙, est étudiée. Avec des données MUSE, les propriétés résolues de la raie Lyα et aussi, pour la première fois, de les raies de CIII] on été dérivées. Le rapport signal sur bruit du spectre obtenu par la combinaison de différentes images multiples révèle des raies d'émission et d'absorption UV qui sont rarement vues dans des galaxies aussi lointaines. Ces raies ont permis d'estimer les propriétés physiques du gaz de cette galaxie (Te~15600 K, ne~300 cm-3, fraction de couverture f~0.4). L'émission Lyα s'étend à plus de 10 kpc autour de l'émission du continu et révèle un profil spectral très uniforme, avec de petites variations non liées à la cinématique de la galaxie mesurée avec les raies d'emission non résonantes. La raie spectrale et le profil de brillance de surface Lyα observés ont été modélisés avec un modèle de transfert radiatif dans un milieu sphérique de gaz en expansion. Je conclus qu'un modèle simple de ce type peut décrire simultanément correctement ces deux observables / Spatially resolved studies of high redshift galaxies can provide essential insight into the inner processes that shape galaxies thought cosmic time. Amongst others, they can allow us to better constrain the merger history of a galaxy, to test hypotheses on the distribution of the underlying mass, to study the density and dust distribution in the neutral gas of early galaxies, or to study the chemical evolution within a disc galaxy. Only in recent decades, thanks to the advent and developments of Integral Field Spectrographs (IFS), it became possible to have this truly 2D vision of galaxies and to 'map' properties such as kinematics, star formation rates and metallicity. Nevertheless, high redshift galaxies that are dimmer due to their distance, are still hard to analyse. A method that allows to overcome this issue is to target objects in the background of strongly lensing clusters. These clusters act as a cosmic telescopes, boosting the total flux of these objects and 'extending' them on the sky, allowing us to study them in a manner would otherwise be only possible with the new generation of telescopes. In my thesis, I present the analysis of 8 of such strongly lensed objects. The first part of the manuscript focuses on a sample of 7 gravitational arcs: extremely extended and magnified but otherwise normal galaxies. These galaxies are magnified by 7 different clusters and have redshifts that range from 0.6 to 1.5 (between 6 to 9 Gyrs ago). These are all rotating discs with masses ranging from 109 to 1011 M⊙ and star formation rates between 3 to 50 M⊙ / yr. While 3 of these galaxies -- AS1063, A370 and MACS0416 -- are star formation main-sequence galaxies, lying less than 0.05 dex away from the Fundamental Metallicity Plane, the remaining four deviate up to 0.4 dex. The global metallicities, measured from several emission lines ratios, are super solar (8.81 to 9.08 [12 + log(O/H)]) and on two objects we measure a metallicity gradient of -0.03 [12+log(O/H)/ kpc] and -0.01 [12+log(O/H)/ kpc]. We measure the ionised gas 2D velocity field and velocity dispersion via strong emission lines (mainly [OII]) finding that all of these galaxies are rotation dominated with V/$\sigma$ ratios between 2 and 9. Accounting for lensing effects, we fit these observed velocity fields using three kinematic models: the arctangent model, the isothermal sphere and exponential disc. We conclude that the isothermal sphere model is marginally a better fit to 4 of the 7 galaxies in our sample, the exponential disc to 2 and 1 by the arctangent model. The second part of the manuscript focuses on a typical (L*, M* = 6 x 109 M⊙) young lensed galaxy at z=3.5, observed with MUSE, for which we obtain 2D resolved spatial information of Lyα and, for the first time, of CIII] emission. The exceptional signal-to-noise of the data reveals UV emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (Te~15600 K, ne~300 cm-3, covering fraction f~0.4) using multiple diagnostics. Inferred stellar and gas-phase metallicities point towards a low metallicity object. The Lyα emission extends over ~10 kpc across the galaxy and presents a very uniform spectral profile, showing only a small velocity shift which is unrelated to the intrinsic kinematics of the nebular emission. The Lyα extension is ~4 times larger than the continuum emission, and makes this object comparable to low-mass LAEs at low redshift, and more compact than the Lyman-break galaxies and Lyα emitters usually studied at high redshift. We model theLyα line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a good description of both observables

No description available.

Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and submillimetre wavelengths. Observations in the submillimetre spectrum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250-500 micron, taking advantage of detector technology developed for the space-based instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a single 10-day flight, BLAST will detect ~10000 extragalactic sources, ~100 times the number detected in 10 years of ground-based observations, and 1000s of Galactic star-forming sources, a large fraction of which are not seen by infrared telescopes. The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Blazars are a subclass of active galactic nuclei whose observable characteristics are generated by relativistic jets of high-energy plasma with trajectories closely aligned to the line of sight. This orientation results in extreme observed phenomena, such as ultraluminous emission, high amplitudes of variability, and high degrees of optical linear polarization. Furthermore, blazars are the most common extragalactic sources of γ-ray photons and have been proposed as sources of high-energy neutrinos. Long-timescale monitoring of blazars has revealed relatively quiescent states interspersed with active states featuring dramatic brightening events, with timescales ranging from months to years. New, high-time-resolution observations of blazars are revealing dramatic variability on timescales as short as several minutes, the physical drivers of which are not well understood. In this dissertation, I focus on observational signatures that can potentially identify these mechanisms. To characterize this variability, I combine observations of blazars from many telescopes, obtaining a comprehensive view of events occurring in the jets. Using the Very Long Baseline Array, I investigate moving and quasi-stationary features in the parsec-scale jets of 38 blazars. I find that the flow speeds, orientation, brightness temperatures, and opening angles of the jets in flat-spectrum radio quasars (FSRQs), BL Lacertae type objects (BL Lac objects), and radio galaxies (RGs) are statistically different, with FSRQs having the highest speeds and smallest viewing angles. Focusing on a typical source of each subclass, I characterize the optical variability observed at 2-min cadence (with the Transiting Exoplanet Survey Satellite), at gamma-ray energies (Fermi Large Area Telescope), X-ray energies (NICER, NuSTAR, and Swift satellites), and optical (ground-based instruments, especially, the Perkins telescope), including linear polarization measurements. I find that the minimum timescale of RG variability is longer than those of the FSRQ and BL Lac object, and is likely caused by changes in the accretion disk. In contrast, the variability in the FSRQ and BL Lac object can be associated with shocks, magnetic reconnections, and turbulence in the jet. The unprecedented availability of data, which promises to expand in the future, represents a new phase of observational astronomy that provides valuable information on changes in the jets of blazars.

No description available.

No description available.

No description available.