Cette thèse explore la formation, l’évolution et la structure des galaxies spirales à l’aide de simulations, en mettant l’accent sur le disque. Elle s'appuie sur nos simulations hydrodynamiques à N-corps mettant en scène une fusion majeure entre deux galaxies à disque à haut redshift, chacune en possession d’un halo de gaz chaud. Les disques des progéniteurs sont détruits par la fusion, et un disque étendu se forme dans la galaxie ainsi obtenue à partir d’étoiles nouvellement formées, la formation stellaire étant alimentée par le halo de gaz. A la fin de la simulation, la nouvelle galaxie montre toutes les propriétés d’une galaxie spirale, prouvant pour la première fois avec des simulations comment une galaxie de type tardif peut être créée par une fusion majeure.Dans cette thèse sont analysées plusieurs propriétés des galaxies ainsi obtenues, comme la migration stellaire, la rotation angulaire de la barre, et les profils radiaux de densité surfacique. Ce dernier point en particulier constitue une partie importante de mon travail, le fit de ces profils permettant d'obtenir les grandeurs caractéristiques du disque. Nos disques montrent en effet un profil de type II (troncature vers le bas) dont il est possible d'extraire les longueurs d'échelle et le rayon de troncature. Le but est notamment de chercher ce qui module les valeurs de ces paramètres (ceux-ci étant très différents d'une simulation à l'autre), ainsi que les phénomènes à l'origine de ce profil spécifique. Enfin, certains disques de type III (troncature du profil vers le haut) obtenus pour des simulations de galaxies isolées sont présentés et analysés, afin de comprendre leur provenance. / This thesis explores the formation, evolution and structure of spiral galaxies using simulations, with an emphasis on the disc component. It is based on our N-body/SPH simulations involving a major merger between two disc galaxies at high redshift, both in possession of a hot gaseous halo. The discs of the progenitors are destroyed by the merger, and a well-extended disc forms in the remnant galaxy from newly born stars, star formation being fuelled by the gaseous halo. By the end of the simulation, the remnant galaxy shows all the properties of a spiral galaxy, proving for the first time in simulations how a late-type galaxy can be created from a major merger.In this thesis, several properties of the remnant galaxy are analysed, such as the stellar migration, the bar pattern speed, and the surface density radial profiles. This last point in particular represents a significant part of my work, using fits of the profiles to obtain the characteristic parameters of the disc. Our discs show a type II profile (downbending truncation), so that we can derive their scalelengths and truncation radius. The goal is to understand what determines the values of these parameters (which are very different from one simulation to another), as well as the origin of this specific profile. Finally, some type III discs (upbending truncation) obtained for simulations of isolated galaxies are presented and analysed, in order to investigate their formation mechanism.

Cosmological simulations suggest a strong correlation between high optical-depth Lya absorbers, which arise from the intergalactic medium, and 3D mass overdensities on scales of 10-30 h(-1) comoving Mpc. By examining the absorption spectra of similar to 80,000 QSO sight lines over a volume of 0.1 Gpc(3) in the Sloan Digital Sky Survey III (SDSS-III), we have identified an extreme overdensity, BOSS1441, which contains a rare group of strong Lya absorbers at z = 2.32 +/- 0.02. This absorber group is associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using Mayall/MOSAIC narrowband and broadband imaging, we detect Lya emitters (LAEs) down to 0.7 x L-Ly alpha ' * a and reveal a large-scale structure of LAEs in this field. Our follow-up LBT observations have spectroscopically confirmed 20 galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of 10.8 +/- 2.6 on a 15 comoving Mpc scale, which could collapse to a massive cluster with M greater than or similar to 10(15) M-circle dot at z similar to 0. This overdensity is among the most massive large-scale structures at z similar to 2 discovered to date.

We present the first discoveries from a survey of z greater than or similar to 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg(2) of sky down to z(AB) similar to 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < + 60 degrees, reaching J(VEGA) similar to 19.6 (5-sigma). The combination of these data sets allows us to discover quasars at redshift z greater than or similar to 7 and to conduct a complete census of the faint quasar population at z greater than or similar to 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z greater than or similar to 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z similar to 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 angstrom being M-1450 = -25.83 and M-1450 = -25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z greater than or similar to 6. The new z = 6.63 quasar has an absolute magnitude of M-1450 = -25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z greater than or similar to 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield similar to 200 z similar to 6 quasars to z(AB) < 21.5, similar to 1000 z similar to 6 quasars to z(AB) < 23, and similar to 30 quasars at z > 6.5 to J(VEGA) < 19.5.

This article reports a measurement of the proper motion of Leo II, a dwarf galaxy that is a likely satellite of the Milky Way, based on imaging with the Hubble Space Telescope and Wide Field Camera. 3. The measurement uses compact background galaxies as standards of rest in both channels of the camera for two distinct pointings of the telescope, as well as a QSO in one channel for each pointing, resulting in the weighted average of six measurements. The measured proper motion in the the equatorial coordinate system is (mu(alpha), mu(delta))= (-6.9 +/- 3.7, -8.7 +/- 3.9) mas century(-1) and in the Galactic coordinate system it is (mu(l), mu(b)) = (6.2 +/- 3.9, -9.2 +/- 3.7) mas. century(-1). The implied space velocity with respect to the Galactic center is (Pi, Theta, Z) =(-37 +/- 38, 117 +/- 43, 40 +/- 16) km s(-1) or, expressed in Galactocentric radial and tangential components, (V-r, V-tan) = (21.9 +/- 1.5, 127 +/- 42) km s(-1). The space velocity implies that the instantaneous orbital inclination is 68 degrees, with a 95% confidence interval of (66 degrees, 80 degrees). The measured motion supports the hypothesis that Leo. II, Leo. IV, Leo. V, Crater. 2, and the globular cluster Crater fell into the Milky Way as a group.

We present a measurement of the abundance of carbon monoxide in the early universe, utilizing the final results from the CO Power Spectrum Survey (COPSS). Between 2013 and 2015, we performed observations with the Sunyaev-Zel'dovich Array to measure aggregate CO emission from z similar to 3 galaxies with the intensity mapping technique. Data were collected on 19 fields, covering an area of 0.7 square degrees, over the frequency range 27-35 GHz. With these data, along with data analyzed in COPSS I, we are able to observe the CO(1-0) transition within the redshift range z = 2.3-3.3 for spatial frequencies between k = 0.5-10 h Mpc(-1), spanning a comoving volume of 4.9 x 10(6) h(-3) Mpc(3). We present estimates of contributions from continuum sources and ground illumination within our measurement. We constrain the amplitude of the CO power spectrum to P-CO = 3.0(-1.3)(+1.3) x 10(3) mu K-2(h(-1) Mpc)(3), or Delta(2)(CO)(k=1 h Mpc(-1)) = 1.5(-0.7)(+0.7) x 10(3) mu K-2, at 68% confidence, and PCO > 0 at 98.9% confidence. These results are a factor of 10 improvement in sensitivity compared to those of COPSS I. With this measurement, we constrain on the CO(1-0) galaxy luminosity function at z similar to 3. Assuming that CO emission is proportional to halo mass and using theoretical estimates of the scatter in this relationship, we constrain the ratio of CO(1-0) luminosity to halo mass to A(CO) = 6.3(-2.1)(+1.4) x 10 (7) L circle dot M circle dot-1. Assuming a Milky Way-like linear relationship between CO luminosity and molecular gas mass, we estimate a mass fraction of molecular gas of f(H2) = 5.5(-2.2)(+3.4) x 10(-2) for halos with masses of similar to 10(12)M(circle dot). Using theoretical estimates for the scaling of molecular gas mass fraction and halo mass, we estimate the cosmic molecular gas density to be rho(z similar to 3) (H-2) = 1.1(-0.4)(+0.7) x 10(8) M(circle dot)Mpc(-3).

We present a catalog of all CO (J = 4-3 through J = 13-12), [ C I], and [ N II] lines available from extragalactic spectra from the Herschel SPIRE Fourier Transform Spectrometer (FTS) archive combined with observations of the low-J CO lines from the literature and from the Arizona Radio Observatory. This work examines the relationships between L-FIR, L'(CO), and L-CO/L-CO,L-1-0. We also present a new method for estimating probability distribution functions from marginal signal-to-noise ratio Herschel FTS spectra, which takes into account the instrumental "ringing" and the resulting highly correlated nature of the spectra. The slopes of log(L-FIR) versus log (L'(CO)) are linear for all mid- to high-J CO lines and slightly sublinear if restricted to (ultra) luminous infrared galaxies ((U) LIRGs). The mid-to high-J CO luminosity relative to CO J - 1-0 increases with increasing L-FIR, indicating higher excitement of the molecular gas, although these ratios do not exceed similar to 180. For a given bin in L-FIR, the luminosities relative to CO J = 1-0 remain relatively flat from J = 6-5 through J = 13-12, across three orders of magnitude of L-FIR. A single component theoretical photodissociation region (PDR) model cannot match these flat SLED shapes, although combinations of PDR models with mechanical heating added qualitatively match the shapes, indicating the need for further comprehensive modeling of the excitation processes of warm molecular gas in nearby galaxies.

Le fond diffus infrarouge est la contribution de toutes les galaxies infrarouges intégrée sur toute l’histoire de l’Univers. Il émet entre 8 et 1000 µm et à un pic vers 200 µm. On résout une large fraction de ce fond dans l’infrarouge proche mais seule une petite fraction l’est dans l’infrarouge moyen et lointain à cause de la confusion. Les sources les plus faibles sont perdues dans le bruit de confusion. Cela forme des fluctuations de brillance, les anisotropies du fond diffus infrarouge. L’étude de ces fluctuations permet l’étude des galaxies sous le seuil de détection, donc des galaxies les plus faibles. Grâce au spectre de puissance on peut mesurer la puissance conte- nue dans ces fluctuations en fonction de l’échelle spatiale. Cette mesure contient, entre autre, le regroupement des galaxies infrarouges. Dans un premier temps, j’ai isolé du spectre de puissance d’une carte infrarouge, le spectre de puissance dû uniquement aux galaxies infrarouges. En effet, aux grandes échelles spatiales, il est contaminé par l’émission des cirrus Galactiques. Ces cirrus sont des nuages d’hydrogène neutre, tracés par la raie à 21 cm. J’ai donc utilisé des données à 21 cm pour estimer l’émission infrarouge de ces cirrus pour ensuite la soustraire aux cartes infrarouge à 100 et 160 µm. Cela m’a aussi permis de faire une mesure précise du niveau absolu du fond diffus infrarouge à ces longueurs d’onde. Afin d’analyser ces spectres de puissances, j’ai mis en place un modèle de regroupement des galaxies infrarouges reliant un modèle d’évolution des galaxies infrarouge reproduisant les données existantes dont celles d’Herschel et un modèle de halo. C’est un modèle complétement paramétré ce qui permet l’étude des dégénérescences de ces paramètres. J’en ai aussi tiré des mesures physiques et leur évolution avec la longueur d’onde. De plus, j’ai ajusté les données existantes de 100 à 1380 µm. Grâce au modèle on peut déterminer les contributions en redshift à chaque longueur d’onde. Les courtes longueurs d’onde tracent les bas redshifts alors que les grandes longueurs d’onde tracent les hauts redshifts. Cependant la contribution des bas redshifts est loin d’être négligeable à ces longueurs d’onde. Afin de déterminer l’évolution du regroupement avec le redshift des cartes des anisotropies du fond diffus infrarouge sont nécessaires. Je vais expliciter une méthode de séparation de composantes dédiée à cela. / The Cosmic Infrared Background is the contribution of all infrared galaxies integrated on the history of the Universe. It emits between 8 and 1000 um with a peak around 200 um. A large fraction of this background is resolved into sources in the near infrared but only a tiny fraction is in the mid and far infrared because of confusion. The least luminous sources are lost in the confusion noise which forms brightness fluctuations, the anisotropies of the cosmic infrared background. The study of these fluctuations enables the study of the galaxies below the detection threshold, thus the less luminous galaxies. Thanks to the power spectrum we can measure the power contained in these fluctuations as a function of the scale. This measure contains, among others, the clustering of the infrared galaxies. First, I have isolated from the power spectrum of an infrared map, the power spectrum only due to infrared galaxies. Indeed, at large spatial scales, it is contaminated by the emission of Galactic cirrus. These cirrus are clouds of neutral hydrogen traced by the 21 cm line. Therefore, I made use of data at 21 cm to estimate the infrared emission of these cirrus that I have then subtracted from infrared maps at 100 and 160 um.This has also enabled me to compute the absolute level of the cosmic infrared background at these wavelengths. In order to analyse these power spectra, I developped a model of clustering of infrared galaxies. To do so I linked a model of evolution of galaxies that reproduces very well existing data including those of Herschel and a halo model. This is a fully parametric model that enables the study of the degeneracies of these parameters. I was also able to study the evolution with the wavelength of several physical measures. Furthermore, I fitted data from 100 um to 1380 um. Thanks to that model, I can determine the redshift distribution at each wavelength. Short wavelength probe small redshifts whereas long wavelength probe high redshifts. However the contribution of small redshift is far from being negligeable at long wavelength. As a long term purpose of determining the evolution of the clustering if the infrared galaxies, maps of the anisotropies of the cosmic infrared background are needed. I will then detail a component separation method dedicated to this problem.

We present high-resolution X-ray imaging data from the ACIS-S instrument on the Chandra telescope of the nearby interacting galaxy group NGC 4410. Four galaxies in the inner portion of this group are clearly detected by Chandra, including the peculiar low-luminosity radio galaxy NGC 4410A. In addition to a nuclear point source, NGC 4410A contains diffuse X-ray emission, including an X-ray ridge extending out to about 12″ (6 kpc) to the northwest of the nucleus. This ridge is coincident with an arc of optical emission-line gas, which has previously been shown to have optical line ratios consistent with shock ionization. This structure may be due to an expanding superbubble of hot gas caused by supernovae and stellar winds or by the active nucleus. The Chandra observations also show four or five possible compact ultraluminous X-ray (ULX) sources (L X ≥ 10 39 ergs s -1) associated with NGC 4410A. At least one of these candidate ULXs appears to have a radio counterpart, suggesting that it may be due to an X-ray binary with a stellar-mass black hole, rather than an intermediate-mass black hole. In addition, a faint diffuse intragroup X-ray component has been detected between the galaxies (L X ∼ 10 41 ergs s -1). This supports the hypothesis that the NGC 4410 group is in the process of evolving via mergers from a spiral-dominated group (which typically has no X-ray-emitting intragroup gas) to an elliptical-dominated group (which often has a substantial intragroup medium).

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