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GRAVITY+ is the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) with wide-separation fringe tracking, new adaptive optics, and laser guide stars on all four 8~m Unit Telescopes (UTs), for ever fainter, all-sky, high contrast, milliarcsecond interferometry. Here we present the design and first results of the first phase of GRAVITY+, called GRAVITY Wide. GRAVITY Wide combines the dual-beam capabilities of the VLTI and the GRAVITY instrument to increase the maximum separation between the science target and the reference star from 2 arcseconds with the 8 m UTs up to several 10 arcseconds, limited only by the Earth's turbulent atmosphere. This increases the sky-coverage of GRAVITY by two orders of magnitude, opening up milliarcsecond resolution observations of faint objects, and in particular the extragalactic sky. The first observations in 2019 - 2022 include first infrared interferometry of two redshift $z\sim2$ quasars, interferometric imaging on the binary system HD 105913A, and repeated observations of multiple star systems in the Orion Trapezium Cluster. We find the coherence loss between the science object and fringe-tracking reference star well described by the turbulence of the Earth's atmosphere. We confirm that the larger apertures of the UTs result in higher visibilities for a given separation due to larger overlap of the projected pupils on sky and give predictions for visibility loss as a function of separation to be used for future planning., Comment: 15 pages, 12 figures, 5 tables. Accepted by A&A

Combining adaptive optics and interferometric observations results in a considerable contrast gain compared to single-telescope, extreme AO systems. Taking advantage of this, the ExoGRAVITY project is a survey of known young giant exoplanets located in the range of 0.1'' to 2'' from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, GRAVITY will measure non-Keplerian perturbations due to planet-planet interactions in multi-planet systems and measure dynamical masses. Over time, repetitive observations of the exoplanets at medium resolution ($R=500$) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K-band has the unique properties that it contains many molecular signatures (CO, H$_2$O, CH$_4$, CO$_2$). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM. Further, we will use the parameter-retrieval algorithm petitRADTRANS to constrain the C/O ratio of the planets. Ultimately, we plan to produce the first C/O survey of exoplanets, kick-starting the difficult process of linking planetary formation with measured atomic abundances., SPIE 2020, invited talk

Boxy and peanut-shaped bulges are seen in about half of edge-on disc galaxies. Comparisons of the photometry and major-axis gas and stellar kinematics of these bulges to simulations of bar formation and evolution indicate that they are bars viewed in projection. If the properties of boxy bulges can be entirely explained by assuming they are bars, then this may imply that their hosts are pure disc galaxies with no classical bulge. A handful of these bulges, including that of the Milky Way, have been observed to rotate cylindrically, i.e. with a mean stellar velocity independent of height above the disc. In order to assess whether such behaviour is ubiquitous in boxy bulges, and whether a pure disc interpretation is consistent with their stellar populations, we have analysed the stellar kinematics and populations of the boxy or peanut-shaped bulges in a sample of five edge-on galaxies. We placed slits along the major axis of each galaxy and at three offset but parallel positions to build up spatial coverage. The boxy bulge of NGC3390 rotates perfectly cylindrically within the spatial extent and uncertainties of the data. This is consistent with the metallicity and alpha-element enhancement of the bulge, which are the same as in the disk. This galaxy is thus a pure disc galaxy. The boxy bulge of ESO311-G012 also rotates very close to cylindrically. The boxy bulge of NGC1381 is neither clearly cylindrically nor non-cylindrically rotating, but it has a negative vertical metallicity gradient and is alpha-enhanced with respect to its disc, suggesting a composite bulge comprised of a classical bulge and bar (and possibly a discy pseudobulge) [abridged] Even this relatively small sample is sufficient to demonstrate that boxy bulges display a range of rotational and population properties, indicating that they do not form a homogeneous class of object., MNRAS accepted. 10 pages

Item does not contain fulltext Pathways Through an Eclectic Universe, 23 april 2007

Interstellar absorption lines of the C2 (2-0) Phillips band at 8750 A have been searched for in the spectra of southern stars. Seventeen lines originating from the lowest eight rotational levels have been detected toward Chi Oph, and eleven lines originating from the lowest five rotational levels toward HD 154368 and 147889. No C2 lines were seen toward HD 149404. A recently developed theory has been used to extract information about the density, temperature or strength of the radiation field in the line-forming interstellar regions from the observed rotational populations. The results are compared with those obtained from other molecular observations. Toward Chi Oph, the interstellar radiation field appears enhanced in the ultraviolet part of the spectrum relative to the infrared part. The C2 data suggest a higher kinetic temperature for the material in front of HD 147889 than is inferred from radio observations.

At the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The second is dark energy, an enigmatic component responsible for the accelerated expansion of the Universe. Under these two forces, matter in the Universe organizes itself in the so-called cosmic web. The nodes of this network are large dark matter haloes, and this thesis explores how their boundaries provide information about the nature of dark energy and cosmology. Chapters 3 and 4 present robust theoretical predictions for this titular edge and discuss its simple physical interpretation. Chapters 2 and 5 corroborate these results by presenting measurements of this feature in weak-lensing data. The last scientific chapter of this thesis is a collection of studies in gravitational-wave physics. This chapter explores how these spacetime ripples observed from across the cosmos can be used to detect alternative theories of gravity.

OB associations are loose groups of young, massive stars. They constitute the last stage of the massive starformation process, and the context in which new stars are formed. Although OB associations have long been studied, it is not clear how they form and disperse in the field and what are the characteristics of their stellarpopulations. Further, not all O and B stars can be associated to groups or clusters, and a fraction of them moves at very high velocity: these are the so-called runaway stars.The data of the Gaia satellite are crucial to unravel the structure and star formation history of the young associations, as they allow to study their spatial structure, kinematics, and ages with unprecedented precision.In this thesis, I studied the properties of the stellar groups in the Orion OB association and the three dimensional arrangement of young stars in the solar neighbourhood, providing a view of the spatial configuration of young star forming regions within 500 pc from the Sun.I further analysed the properties of massive runaway stars, aiming at a better understanding of massive star evolution and of the dynamical processes occurring within dense stellar clusters

The high velocity tail of the total velocity distribution of stars provides essential insight into fundamental properties of the Galaxy. Hypervelocity stars (HVSs), travelling on unbound orbits coming from the Galactic Centre, are powerful tracers of the underlying Galactic gravitational potential, and can shed light on the stellar population in the proximity of our massive black hole. Runaway stars, ejected from the stellar disk, provide information on binary evolution and stellar clusters' dynamical processes. The advent of the data from the European Space Agency satellite Gaia has revolutionized our knowledge on high velocity stars. In my PhD thesis entitled "Hunting for the fastest stars in the Milky Way" I present my work on searching for the fastest stars in the Milky Way. I start by presenting our modelling work on predicting the HVS population expected to be contained in the Gaia catalogue. Then I illustrate the data mining techniques built and implemented to find these rare objects in the first and second data release of Gaia. Finally, I conclude discussing how HVSs can be used to constrain the Galactic dark matter halo and the binary population in the Galactic Centre.

In this thesis we explore new techniques to study the dark and luminous matter in the outskirts of galaxies. To determine the mass and shape of the dark matter halo around the early-type galaxy NGC 2974, we measure the kinematics of its large neutral gas ring. We combine these large-scale kinematics with the central kinematics of the ionised gas to construct mass models of this galaxy. For galaxies that do not contain neutral gas, we use integral-field spectroscopy to measure the stellar kinematics at large radii. Briefly, we use the spectrograph as a "photon-collector", to obtain spectra with sufficient signal-to-noise. The kinematics are used to model the dark haloes around the galaxies NGC 2549, NGC 3379 and NGC 821. We also measure the line strengths from the spectra to determine the properties of the stellar population in the outer parts of these systems. Finally, we take a look in the high-redshift Universe, by studying the Lyman Alpha emission of a system at redshift 3.1 (LAB1). We obtain integral-field spectra to study the distribution of the ionised gas, as well as the emission profile, and discuss possible formation and ionisation scenarios.

The main goal of the research presented in this thesis is to gain a better insight into the dynamical structure and evolution of galaxies, globular clusters and other stellar systems. In nearby stellar systems, we look for the fossil record of their formation by constructing realistic models that fit their photometric and (two-dimensional) spectroscopic observations in detail. A large fraction of this thesis is devoted to the development and validation of triaxial dynamical Schwarzschild models, which we apply to several elliptical galaxies.

Starburst galaxies undergo a phase of vigorous star formation. In these galaxies, gas is turned into stars at such a high rate, that the reservoir of available gas is quickly emptied. Numerous massive, bright star clusters are created from the giant molecular clouds. They form an ideal laboratory for the study of rapid star formation. In this thesis, a detailed study of active star-forming regions in the starburst galaxies NGC 4038/4039 and M83 is presented. Sincethe stars are hidden from view by large quantities of dust, we observe them at infrared wavelengths. We address the properties of the newly formed star clusters and the surrounding interstellar matter.

Dark matter assembles to form massive halos, attracting gas particles that coalesce to form stars, and the photons produced by these sources are sent into the void. An accurate description of the transport of particles is therefore the essential ingredient for understanding how the Universe evolved into its present form. Of all these transport processes, the transfer of radiation is the most elusive: the non- locality and high-dimensionality of the problem currently put realistic simulations out of reach. In this thesis, we present a novel approach to this transport problem, combining methods from mathematics and statistical physics in a practical computer code. Its speed and versatility allow us, for the first time, to make realistic simulations in radiative gas dynamics and in cosmology. Because of the general mathematical/physical character of our methods, we expect them to be useful for transport phenomena in general.

The main goal of the PhD research described is to gain insight in the dynamical structure and evolution of galaxies, globular clusters and other stellar systems. For nearby stellar systems, realistic axisymmetric and triaxial dynamical models are constructed that fit their photometric and (two-dimensional) spectroscopic observations in detail. For early-type galaxies at higher redshift, the Fundamental Plane is used to investigate the evolution of their mass-to-light ratios. The connection of the results from both approaches allows a better understanding of the formation history of these stellar systems.

In this thesis I discuss recent observations of distant (z > 2) radio galaxies. There is strong evidence that radio galaxies are the progenitors of the brightest cluster ellipticals and are among the most luminous and massive galaxies at any epoch, allowing relatively detailed studies of their formation process out to large distances. Submillimeter emission has been detected in many, implying star formation rates of order 1000 Msun/yr over scales of tens of kpc, consistent with a scenario in which these galaxies are currently forming the bulk of their eventual stellar population. Many radio galaxies also host giant (~ 150 kpc) emission line nebulae. We obtaind very deep narrow-band Ly-a images for a select few of these. The observations show spectacular detail with a wealth of morphological structure, such as extended (~ 80 kpc) filamentary structures, giving insight in feedback processes during their formation. I discuss the possible origin and the ionization source of these halos in connection with the sub-mm results, and discuss possible implications for theories of galaxy formation.

Ova disertacija usredotocena je na posebnu temu astronomije: nastanak i evolucija elipticnih galaksija. IStrazuje se aktivnost, struktura, kinematika i dinamika bliskih galaksija ranog tipa.

The Milky Way is the cornerstone of our understanding of galaxies. The structureand kinematics of its gas and stars can be studied in unique detail due totheir relative proximity. However, being located well within the Galactic diskand thereby observing the Milky Way in non–linear projection makes it difcultto properly map its large-scale morphology.One of the interesting ndings has been that observations of molecular lineemission (CO, HI) and stellar motions show signatures of a Galactic Bar in the innerGalaxy. However, its characteristics such as elongation, thickness and viewingangle are still poorly constrained. One of the main obstacles has been thestrong obscuration by interstellar dust toward the inner Galaxy, which makesoptical studies of the stellar population in that region almost impossible. Theextinction is less severe at near- and mid-infrared wavelengths. To characterisethe structure and formation history of the Milky Way, several infrared surveyswere conducted during the past decade: ISOGAL, MSX, DENIS, 2MASS. Thesedata contain a wealth of information on the structure of the stellar populationsthat has yet to be fully analysed. Having entered a golden age for Galactic astronomy,soon even more detailed imaging and spectroscopy will be provided bythe Spitzer Space Telescope, while the GAIA satellite will provide unprecedentedastrometry.My thesis research has focused on the structure and stellar population of theinner 4 kpc of the Milky Way. I have analysed data from recent infrared surveysand obtained SiO radio maser line observations of late-type giants to study thestar formation history and the gravitational potential of the inner Galaxy. Withages ranging from less than 1 to 15 Gyr, the infrared-luminous late-type giantstars are representative of the bulk of the Galactic stellar population, and hencetrace its star formation history. Their spatial abundance variation maps the stellarmass distribution, and thereby probes the Galactic gravitational potential. Thereddening of their spectral energy distribution can be used to map the interstellarextinction. Their envelopes often emit strong molecular masers (OH, SiO) thatcan be detected throughout the Galaxy, and through the precise measurement ofthe maser line velocity they reveal the stars' line-of-sight velocities. Thereforethey are ideal tracers of the Galactic kinematics and gravitational potential.