Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 177-196).

This Thesis explores the use of independent dynamical probes (multiple populations, gravitational lensing) to infer the prope1ties of Dark Matter (DM) haloes and investigate scenarios of galaxy formation. It begins with a study of the virial properties (flattening and global anisotropy) of stellar populations in different DM profiles. General theorems are presented, with some application to the Milky Way potential (DM flattening and density profile) as probed by the thick disk, stellar halo and rotation curve. A powerful outcome of virial methods applied to multiple populations is the distinction between DM cusps or cores in nearby dwaif Spheroidal galaxies, in particular Seu lptor and Fornax. Modelling based upon the Jeans equations is reformulated so that it involves just the direct observables (surface density and velocity dispersion), which enables a simultaneous exploration of photometric and dynamical prope1ties. This is applied to different systems. First, probes of DM in early-type galaxy gravitational lenses are devised and the mass-bias underliying some common assumptions in the literature is quantified. Second, when studying the Globular Cluster (GC) system of the nearby Elliptical M87, this new approach yields information on the GC subpopulations, the luminous mass and DM profile. Inference on the GC orbital structure is discussed, with an eye to the processes of assembly and evolution that my have produced it. The general aim of this Thesis is the development of simple, yet flexible and robust, methods to study DM profiles in spheroidal or ellipsoidal galaxies of different sizes and masses. The combined treatment of photometry and dynamics yields appreciable insight even when the data are not enough to justify more elaborate modelling techniques.

No description available.

Thesis (Ph.D.) - University of St Andrews, September 2008.

We study the motion of giant stars in the Solar neighbourhood and what they tell us about the dynamics of the Galaxy: we thus contribute to the huge project of understanding the structure and evolution of the Galaxy as a whole. We present a kinematic analysis of 5952 K and 739 M giant stars which includes for the first time radial velocity data from an important survey performed with the CORAVEL spectrovelocimeter at the Observatoire de Haute Provence. Parallaxes from the Hipparcos catalogue and proper motions from the Tycho-2 catalogue are also used. A maximum-likelihood method, based on a bayesian approach, is applied to the data, in order to make full use of all the available stars, and to derive the kinematic properties of the subgroups forming a rich small-scale structure in velocity space. Isochrones in the Hertzsprung-Russell diagram reveal a very wide range of ages for stars belonging to these subgroups, which are thus most probably related to the dynamical perturbation by transient spiral waves rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same area of velocity space is that they have been put there by the spiral wave associated with their formation, while the kinematics of the older stars of our sample has also been disturbed by the same wave. The emerging picture is thus one of "dynamical streams" pervading the Solar neighbourhood and travelling in the Galaxy with a similar spatial velocity. The term "dynamical stream" is more appropriate than the traditional term "supercluster" since it involves stars of different ages, not born at the same place nor at the same time. We then discuss, in the light of our results, the validity of older evaluations of the Solar motion in the Galaxy. We finally argue that dynamical modeling is essential for a better understanding of the physics hiding behind the observed kinematics. An accurate axisymmetric model of the Galaxy is a necessary starting point in order to understand the true effects of non-axisymmetric perturbations such as spiral waves. To establish such a model, we develop new galactic potentials that fit some fundamental parameters of the Milky Way. We also develop new component distribution functions that depend on three analytic integrals of the motion and that can represent realistic stellar disks.

Thesis (Ph.D.)--Ohio University, March, 2004. / Title from PDF t.p. Includes bibliographical references (p. 95-101)

The stellar halo of the Milky Way is populated by mostly old and metal-poor stars. As dynamical timescales are of order ~Gyrs at these large distances, accreted stellar substructures, such as dwarf galaxies or globular clusters, survive here as coherent entities longer than anywhere else in the Galaxy. These substructures represent our “fossil record” which can be used to reconstruct the Galaxy’s complex past. In this work, we seek to identify the structures found in the far reaches of the stellar halo as a step towards a correct interpretation of this fossil record. The advent of all-sky surveys in the Gaia era has ignited a prosperous period for this field of Galactic archaeology, but exploring the distant Milky Way (>10 kpc) with Gaia is difficult. Parallax measurements are much less accurate beyond the Solar neighborhood, though Gaia’s proper motions remain useful out to large radii. To push Gaia into the distant Galaxy, we combined these astrometric data with u-band photometry from the Canada-France Imaging Survey (CFIS). We exploited CFIS’ excellent photometric quality and depth (which extends 3 magnitudes deeper than that of the Sloan Digital Sky Survey) to use blue horizontal branch stars (BHBs) as a tracer population with well-measured distances. We first examined the distribution of BHBs using the OPTICS (Ordering Points To Identify the Clustering Structure) clustering algorithm to visualize the hierarchical nature of outer halo substructure. We then identified several well-known satellites, including a group of stars in the vicinity of a distant globular cluster (NGC 5466). Analysis of their kinematics suggested a few of these BHBs outside the cluster’s tidal radius were co-moving with NGC 5466, implying they may be tidal debris from this system. Interestingly, a stream had previously been detected extending from this globular cluster. However, its properties had not been studied in the decade since its discovery, and previous dynamical models were unable to reproduce many of the reported features. As one of the (allegedly) longest globular cluster streams on the sky - and given its distance and utility to constrain the Milky Way’s mass at large Galactic radius - we sought to explore this structure further. We subsequently used red giant branch stars (RGBs) identified in CFIS to try to better quantify the characteristics of the putative stream. We were able to filter these data and obtain a sample of stars that are fully consistent with stream membership and which span approximately 31 degrees of sky. Combined with the BHBs, we used these populations to trace the path of the stream, its distance and distance gradient across the stream’s longitude, and additionally estimated a lower limit to the stream’s luminosity. Our measurements suggest that the stream is at least 11% of the luminosity of the cluster. We then compared our observational data to dynamical models, which showed generally good agreement with the observed stream. This success reflects the updated properties of data measured in this work, and the inclusion of new data (especially proper motions). Our model suggests that the pericenter and apocenter of NGC 5466's orbit are 6.4 and 43 kpc, respectively, resulting in a very eccentric orbit (ε = 0.74). We also find evidence that the cluster experienced a recent interaction (within the past ~100 Myrs) with the Galactic disk, suggesting that the primary source of mass loss in this system may be caused by disk-shocking. The NGC 5466 stellar stream also exhibits an interesting heliocentric gradient in the leading arm, which our simplistic spherical halo model does not fully reproduce. Dynamical experiments with various halo shapes fit to this stream will prove interesting for future work. For local cosmology in particular, long, thin, dynamically cold stellar streams are ideal systems for constraining properties of the Milky Way’s dark matter halo, and streams at large radius are especially useful for measuring the Galaxy's mass interior to the stream. In this respect, we anticipate that NGC 5466 will be exceptionally useful as a probe of the shape, mass, and dark substructure of the Milky Way's distant dark matter halo. / Graduate

We study the motion of giant stars in the Solar neighbourhood and what they tell us about the dynamics of the Galaxy: we thus contribute to the huge project of understanding the structure and evolution of the Galaxy as a whole. <p><p>We present a kinematic analysis of 5952 K and 739 M giant stars which includes for the first time radial velocity data from an important survey performed with the CORAVEL spectrovelocimeter at the Observatoire de Haute Provence. Parallaxes from the Hipparcos catalogue and proper motions from the Tycho-2 catalogue are also used.<p><p>A maximum-likelihood method, based on a bayesian approach, is applied to the data, in order to make full use of all the available stars, and to derive the kinematic properties of the subgroups forming a rich small-scale structure in velocity space. Isochrones in the Hertzsprung-Russell diagram reveal a very wide range of ages for stars belonging to these subgroups, which are thus most probably related to the dynamical perturbation by transient spiral waves rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same area of velocity space is that they have been put there by the spiral wave associated with their formation, while the kinematics of the older stars of our sample has also been disturbed by the same wave. The emerging picture is thus one of "dynamical streams" pervading the Solar neighbourhood and travelling in the Galaxy with a similar spatial velocity. The term "dynamical stream" is more appropriate than the traditional term "supercluster" since it involves stars of different ages, not born at the same place nor at the same time. We then discuss, in the light of our results, the validity of older evaluations of the Solar motion in the Galaxy. <p><p>We finally argue that dynamical modeling is essential for a better understanding of the physics hiding behind the observed kinematics. An accurate axisymmetric model of the Galaxy is a necessary starting point in order to understand the true effects of non-axisymmetric perturbations such as spiral waves. To establish such a model, we develop new galactic potentials that fit some fundamental parameters of the Milky Way. We also develop new component distribution functions that depend on three analytic integrals of the motion and that can represent realistic stellar disks. / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

<p>The barred spiral galaxy M83 (NGC5236) has been observed in the ¹²CO <i>J</i>=1–0 and <i>J</i>=2–1 millimetre lines with the Swedish-ESO Submillimetre Telescope (SEST). The sizes of the CO maps are 100×100, and they cover the entire optical disk. The CO emission is strongly peaked toward the nucleus. The molecular spiral arms are clearly resolved and can be traced for about 360º. The total molecular gas mass is comparable to the total Hi mass, but H₂dominates in the optical disk.</p><p>Iso-velocity maps show the signature of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. The dynamical mass is determined and compared to the gas mass. The pattern speed is determined from the residual velocity pattern, and the locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found.</p><p>A total gas (H₂+Hi+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The star formation rate (SFR) in the disk is estimated using data from various star formation tracers. The different SFR estimates agree well when corrections for extinctions, based on the total gas mass map, are made. The radial SFR distribution shows features that can be associated with kinematic resonances. We also find an increased star formation efficiency in the spiral arms. Different Schmidt laws are fitted to the data. The star formation properties of the nuclear region, based on high angular resolution HST data, are also discussed.</p>

Dans un disque axisymétrique en équilibre, les vitesses galactocentriques radiales et verticales sont théoriquement nulles. Pourtant, de grands relevés spectroscopiques ont révélé que les étoiles du disque de la Voie Lactée sont animées de vitesses non nulles dans les directions radiale et verticale. Les structures en vitesse radiale sont généralement associées aux composantes non-axisymétriques du potentiel. Celles en vitesse verticale non nulle sont souvent associées à des excitations externes. Nous avons montré que la réponse stellaire à une perturbation spirale produit un déplacement radial et des mouvements verticaux non nuls. La structure du champ moyen de vitesse obtenue est cohérente avec les observations. De plus un modèle simple reposant sur une linéarisation des équations d'Euler reproduit naturellement ce résultat. Nous concluons que ces structures observées pourraient aussi être engendrées par des perturbations internes non-axisymétriques. / In an equilibrium axisymmetric galactic disc, the mean galactocentric radial and vertical velocities are expected to be zero everywhere. Recent spectroscopic surveys have however shown that stars of the Milky Way disc exhibit non-zero mean velocities outside of the Galactic plane in both the radial and vertical velocity components. While radial velocity structures have already often been assumed to be linked with non-axisymmetric components of the potential, non-zero vertical velocity structures are usually rather attributed to excitations by external sources. We show that the stellar response to a spiral perturbation induces both a radial velocity flow and non-zero vertical motions. The resulting structure of the mean velocity field is qualitatively similar to the observations. Such a pattern also emerges from an analytic toy model based on linearized Euler equations. In conclusion, non-axisymmetric internal perturbations can also be the source of the observed mean velocity patterns.