Massive star formation takes place in the dense cores of molecular clouds where the stars may be obscured at optical wavelengths. An excellent signpost of a massive young stellar object is the presence of an ultra-compact HII region (UCHii), which is a dense photo-ionised cocoon of gas surrounding the newly formed star. The aim of this project is to develop an assembly of numerical tools, caravela, that can simulate realistic data streams representing high-mass star forming regions in our Galaxy. The synthetic output consists in images and photometric point source catalogues, in the IRAS and Herschel wavebands. In an era when large observational surveys are increasingly important, this tool can produce simulated infrared point-source catalogues of high-mass star forming regions on a Galactic scale. The approach used is to construct a synthetic Galaxy of star-forming regions represented by SED templates. The star-forming regions are distributed randomly along a four spiral arm morphology, although a wide range of geometries can be used including rings and different numbers of spiral arms. The caravela code then observes the synthetic Galaxy to produce simulated images and point source catalogues with appropriate sensitivity and angular resolution. caravela was first used to model the simulated Galaxy by constraining the synthetic output to observations made by IRAS. This numerical tool will allow the user to infer physical properties of the Galactic population of high-mass star forming regions from such observations. Second, the selected model was again observed with caravela in Herschel mode. These are therefore predictive results for the future Herschel observations. A model with 4.0×104 compact proto-stars embedded in larger grey-body envelopes (with T = 40 K and linear size scale lIII = 5.0 × 106 AU) is the best-fit model to the IRAS observational data set studied. We found a level of contamination from low- and intermediate-mass objects of " 90%. The modelled data set resulting from the Herschel simulation resulted in the detection of approximately twice as many Herschel objects than IRAS, which is consistent, in a limited way, with the real observed companion clump fraction (CCF) of 0.90 ± 0.07 (Thompson et al., 2006) means that on average there were observed 2 sources per one IRAS source. Our caravela and the real observed CCF are therefore consistent. caravela was coupled with an independent diffuse emission model (Paladini et al., 2007) and the resulting analysis is presented as an interesting seed for the future.

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.

I have investigated the properties of the large scale structure of the nearby Universe using data from the Galaxy and Mass Assembly survey (GAMA). I generated complementary halo mass estimates for all groups in the GAMA Galaxy Group Catalogue (G³C) using a modified caustic mass estimation algorithm. On average, the caustic mass estimates agree with dynamical mass estimates within a factor of 2 in 90% of groups. A volume limited sample of these groups and galaxies are used to generate the large scale structure catalogue. An adapted minimal spanning tree algorithm is used to identify and classify structures, detecting 643 filaments that measure up to 200 Mpc/h, each containing 8 groups on average. A secondary population of smaller coherent structures, dubbed `tendrils,' that link filaments together or penetrate into voids are also detected. On average, tendrils measure around 10 Mpc/h and contain 6 galaxies. The so-called line correlation function is used to prove that tendrils are real structures rather than accidental alignments. A population of isolated void galaxies are also identified. The properties of filaments and tendrils in observed and mock GAMA galaxy catalogues agree well. I go on to show that voids from other surveys that overlap with GAMA regions contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of the galaxies observed by a survey. Finally, I examine the properties of galaxies in different environments, finding that galaxies in filaments tend to be early-type, bright, spheroidal, and red whilst those in voids are typically the opposite: blue, late-type, and more faint. I show that group mass does not correlate with the brightness and morphologies of galaxies and that the primary driver of galaxy evolution is stellar mass.