In this thesis I investigate galaxy evolution by measuring the luminosity functions of galaxies across a wide range in redshift. I measure the abundances of high redshift galaxies in deep HST imaging of the GOODS-North field from the CANDELS survey. I follow this evolution to lower redshift by measuring the luminosity functions of galaxies in ground-based imaging of the XMM-LSS field from the VIDEO survey with optical data from the CFHTLS. First, at high-redshift, I identify 22 candidate z ≈ 7 and 6 candidate z ≈ 8 − 9 galaxies. By comparing the number of candidate galaxies with those found in the GOODS-South field, I determine that cosmic variance is not the dominant source of uncertainty on the number counts. I constrain the Schechter parameters for the UV luminosity function at z ≈ 7 and z ≈ 8 − 9, finding evidence for evolution in the number density of high redshift galaxies. Next, I present the K_s-band luminosity functions in the 1 degree² and 4.5 degree² overlaps between the VIDEO-XMM field and the CFHTLS-D1 and CFHTLS-W1 fields. I measure the luminosity functions with the 1/V_max method over the range 0.2 < z < 3 in VIDEO-CFHTLS-D1, and over the range 0.2 < z < 1.5 in the shallower VIDEO-CFHTLS-W1 field. I find the evolution of these luminosity functions is best described by luminosity dependent density evolution, where the characteristic magnitude has dimmed at a constant rate since z = 3, while the density has increased since z = 3, first rapidly from z = 3 to z ≈ 1.5 and then more slowly from z ≈ 1.5 to z = 0.2. I measure a significant upturn at the faint end of the luminosity function at low redshift. Finally, I compare the VIDEO-CFHTLS-D1 and VIDEO-CFHTLS-W1 luminosity functions with predicted K-band luminosity functions from the Horizon-AGN simulation. I find both an over-prediction in the numbers of faint galaxies and an under-prediction in the numbers of bright galaxies, implying that the feedback from supernovae is insufficient while the feedback from AGN is over-sufficient.

abstract: Numerical simulations are very helpful in understanding the physics of the formation of structure and galaxies. However, it is sometimes difficult to interpret model data with respect to observations, partly due to the difficulties and background noise inherent to observation. The goal, here, is to attempt to bridge this gap between simulation and observation by rendering the model output in image format which is then processed by tools commonly used in observational astronomy. Images are synthesized in various filters by folding the output of cosmological simulations of gasdynamics with star-formation and dark matter with the Bruzual- Charlot stellar population synthesis models. A variation of the Virgo-Gadget numerical simulation code is used with the hybrid gas and stellar formation models of Springel and Hernquist (2003). Outputs taken at various redshifts are stacked to create a synthetic view of the simulated star clusters. Source Extractor (SExtractor) is used to find groupings of stellar populations which are considered as galaxies or galaxy building blocks and photometry used to estimate the rest frame luminosities and distribution functions. With further refinements, this is expected to provide support for missions such as JWST, as well as to probe what additional physics are needed to model the data. The results show good agreement in many respects with observed properties of the galaxy luminosity function (LF) over a wide range of high redshifts. In particular, the slope (alpha) when fitted to the standard Schechter function shows excellent agreement both in value and evolution with redshift, when compared with observation. Discrepancies of other properties with observation are seen to be a result of limitations of the simulation and additional feedback mechanisms which are needed. / Dissertation/Thesis / Ph.D. Physics 2012

This thesis presents two analyses of data recorded by the ATLAS detector during proton-proton collisions at the LHC. The first is the implementation of a vertex counting algorithm to measure the luminosity recorded by ATLAS during collisions at a centre-of-mass energy of √s = 8 TeV in 2012. This comprises a Monte Carlo closure test for validation of the method and its corrections, the calibration of the method using the van der Meer scans performed in 2012 and the application of the method to physics runs. It also includes tests of the internal and external consistency of the algorithm and the potential to use this algorithm to measure the luminosity of data collected during proton-proton collisions at √s = 13 TeV.The second analysis is the measurement of the inclusive and purely electroweak production of dijets in association with a Z boson, performed using the 3.2 fb−1 of data collected during collisions at a centre-of-mass energy of √s = 13 TeV in 2015. Cross-section measurements are presented for five fiducial regions, each of which has a different sensitivity to the electroweak component of the Zjj production. Data and Monte Carlo predictions are compared and found to be in reasonable agreement for most cases. The electroweak Zjj production cross-section is then extracted in a fiducial region where this contribution is enhanced. This measurement is also in good agreement with the Monte Carlo prediction. These first 13 TeV measurements will set the scene for studies of weak boson fusion, both within the Standard Model and in new phenomena searches, which will become even more important in Run 2 and the future of the LHC due to the electroweak sector not being as constrained yet, compared to the strong sector, and due to the larger enhancements as a result of a higher √s, where electroweak physics can be most easily extracted.

<p> Globular clusters (GCs) can be divided into two subpopulations when plotted on a colour-magnitude diagram: one red and metal-rich (MR), and the other blue and metal-poor (MP). For each subpopulation, any correlation between colour and luminosity can then be converted into mass-metallicity relations (MMRs).</p> <p> Tracing the MMRs for fifteen GC systems (GCSs) - all around Brightest Cluster Galaxies - we see a nonzero trend for the MP subpopulation but not the MR. This trend is characterised by p in the relation Z=M^p. We find p ~ 0.35 for the MP GCs, and a relation for the MR GCs that is consistent with zero. When we look at how this trend varies with the host galaxy luminosity, we extend previous studies (e.g., Mieske et al, 2006b) into the bright end of the host galaxy sample.</p> <p> In addition to previously presented (B-I) photometry for eight GCSs obtained with ACS/WFC on the HST, we present seven more GCSs. Four of these are newly analysed from HST data, one is previously presented (g-i) photometry obtained with GMOS on Gemini South, and two are the author's newly reduced and analysed (g-i) photometry also obtained with GMOS on Gemini South.</p> <p> Interpretation of these results is important for further understanding the formation and evolution of galaxies within the hierarchical-merging picture, and what process enables the production of two subpopulations.</p> / Thesis / Master of Science (MSc)

No description available.

I analyse an x-ray selected sample of 128 late-type (F-M) stars. These stars were identified as optical counterparts to serendipitous x-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as x-ray sources, the stars were reobserved with an extensive program of optical observations consisting of high- and low-resolution spectroscopy and photometry. Spectral types, luminosity classes, absolute magnitudes, distances, x-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample. I find that Lₓ is correlated with v sin i for single stars. However, Lₓ does not correlate with Ω sin i, which leads me to believe that the correlation seen with v sin i is actually a correlation with radius. Indeed, Lₓ correlates strongly with radius (color, mass) for main sequence stars. This result provides a plausibility argument for rotational saturation in the coronae of late-type stars. Since this sample is flux limited, I use sky coverage and sensitivity information from the Einstein Observatory to calculate the bright end of the x-ray luminosity function for late-type stars. It appears that previously calculated luminosity functions from optically selected samples have underestimated the number of x-ray bright F and G dwarfs. I have also discovered 8 previously uncatalogued M dwarfs within 25 pc of the sun. My sample includes only M dwarfs of spectral type M5 and earlier, 93% of which are "emission" stars (i.e. type Me V), as well as two pre-main sequence M stars. Arguments involving kinematics and stellar rotational velocities are used to estimate the age of these x-ray "bright" M dwarfs; they appear to be quite young (≤ 1-3 x 10⁹ yrs). Since the local space density of x-ray "bright" M dwarfs increases with mass, I infer a longer activity timescale for lower masses. M dwarfs later than M5 lie below the sample's x-ray sensitivity limit. An upper limit of log Lₓ = 27.45 is put on their coronal emission. I also present H(α) and Ca II K line fluxes for most members of the M dwarf sample and show that the H(α) and Ca II K luminosities do indeed correlate with Lₓ. However, these chromospheric luminosities are weaker functions of rotation than Lₓ and may, in fact, represent saturated levels of activity. My results are consistent with the hypothesis that the chromosphere is heated by x-rays from the overlying corona. Finally, I discuss two unusual members of the sample which are attractive candidates for the recently proposed class of FK Comae stars.

We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at 1 < z < 3. We use our deep near-ultraviolet imaging from WFC3/UVIS on the Hubble Space Telescope and existing Advanced Camera for Surveys (ACS)/WFC and WFC3/IR imaging of three lensing galaxy clusters, Abell 2744 and MACS J0717 from the Hubble Frontier Field survey and Abell 1689. Combining deep UV imaging and high magnification from strong gravitational lensing, we use photometric redshifts to identify 780 ultra-faint galaxies with M-UV < -12.5 AB mag at 1 < z < 3. From these samples, we identified five new, faint, multiply imaged systems in A1689. We run a Monte Carlo simulation to estimate the completeness correction and effective volume for each cluster using the latest published lensing models. We compute the rest-frame UV LF and find the best-fit faint-end slopes of alpha = -1.56 +/- 0.04, alpha = -1.72 +/- 0.04, and alpha = -1.94 +/- 0.06 at 1.0 < z < 1.6, 1.6 < z < 2.2, and 2.2 < z < 3.0, respectively. Our results demonstrate that the UV LF becomes steeper from z similar to 1.3 to z similar to 2.6 with no sign of a turnover down to MUV = -14 AB mag. We further derive the UV LFs using the Lyman break "dropout" selection and confirm the robustness of our conclusions against different selection methodologies. Because the sample sizes are so large and extend to such faint luminosities, the statistical uncertainties are quite small, and systematic uncertainties (due to the assumed size distribution, for example) likely dominate. If we restrict our analysis to galaxies and volumes above >50% completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values (alpha = -1.55 +/- 0.06, -1.69 +/- 0.07, and -1.79 +/- 0.08 for z similar to 1.3, 1.9, and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of -18.5 < M-UV < -12.5 covered in this study produce the majority (55%-60%) of the unobscured UV luminosity density at 1 < z < 3.

No description available.

Un des principaux objectifs de l'expérience ATLAS auprès du LHC est l'observations ou l'exclusion de nouvelle physique au-delà du Modèle Standard, en passant par les mesures de sections efficaces de production de processus du Modèle Standard. Sachant que le taux de production d'une particule dépends de sa section efficace de production ainsi que de la luminosité, il est necessaire de mesurer cette luminosité avec une grande précision. L'expérience ATLAS possède plusieurs détecteurs capable de mesurer la luminosité, dont les deux principaux: LUCID (Luminosity measurement Using Cerenkov Integrating Detector), et BCM (Beam Condition Monitor). Ces détecteurs sont calibrés absolument pendant des prises de données dédiées appelés van der Meer scans, qui ont permis d'obtenir une erreur systématique sur la détermination de la luminosité de 3.4% en 2010. Afin d'obtenir un maximum de différentes approches à la luminosité, plusieurs autres détecteurs contribuent aux différentes comparaisons. Ce document présente les calorimètres à argon liquide du détecteur ATLAS, et en particulier la mise en route et l'opération de leur système haute-tension. Il est montré qu'en mesurant les courant de ce système haute-tension pendant les prises de données de collisions de protons, il est possible d'obtenir des signaux proportionnels a la luminosité. En calibrant ces courants par rapport a un autre luminomètre, il est montré que cette calibration est stable au niveau de 0.5%. / The main goals of the ATLAS scientific programme are the observation or exclusion of physics beyond the Standard Model (SM), as well as the measurement of production cross-sections of SM processes. As the rate of events N of a given physics process is linked to the cross-section through the luminosity, it is important to measure the luminosity with great precision. The ATLAS experiment has two major luminosity monitors, LUCID (Luminosity measurement Using Cerenkov Integrating Detector), which consists of Cerenkov tubes located around the beam axis 17m away from the interaction point, and BCM (Beam Condition Monitor) which is a diamond-based detector and has both beam-abort and luminosity capabilities. As these detectors provide a relative luminosity measurement, they were absolutely calibrated in 2010 using the van der Meer procedure, achieving a total systematic uncertainty of 3.4%. The ultimate plan is to provide an absolute calibration using the ALFA detector during a run with special beam optics. In order to provide more cross-checks and a better control on the systematic uncertainties, other luminosity handles are always needed. In particular, an independent measurement using the liquid argon forward calorimeter (FCal), based on the readout current of its high-voltage system, has been developed. This document presents the commissioning and operations of the ATLAS liquid argon calorimeter high-voltage system, as well as its usage to perform a luminosity determination. Analysis of the high-voltage currents during LHC collisions and comparisons with other luminosity detectors have led to a calibration of these currents with a precision better than 0.5%.

Celà fait maintenant presque 50 ans qu'on a découvert que la section efficace totale proton-proton augmentait avec l’énergie, alors qu'on pensait précédemment qu'elle deviendrait asymptotiquement constante. Les incertitudes des mesures sur les rayons cosmiques effectuées à haute énergie ne permettent pas de déterminer la forme exacte de l'augmentation de la section efficace avec l’énergie.Le LHC au CERN à Genève fournit des collisions avec une énergie jamais atteinte dans un accélérateur de particule. L’énergie dans le centre de masse était 7 TeV en 2010 – 2011, 8 TeV en 2012 et atteindra 14 TeV dans un futur proche. Le détecteur ATLAS installé sur un des quatre points d'interaction du LHC, est utilisé pour collecter le résultat des collisions proton-proton. Son sous-détecteur ALFA, situé à 240 m du point d'interaction, est utilisé pour détecter les proton résultant des collisions élastiques. ALFA est donc capable, dans certaines conditions particulières de l'optique, de mesurer la section efficace totale et la pente nucléaire.Le travail effectué durant cette thèse a permit de mesurer σtot = 94.88 ± 0.12 stat ± 1.56syst mb et b = 19.45 ± 0.05stat ± 0.31syst GeV-2 à 7 TeV. / It is now nearly fifty years since total proton-proton (pp) cross sections have been found to grow with energy after it was believed for long time that they would become asymptotically constant . The uncertainties of the cosmic ray data, at high energy, do not allow to determine the exact growth with energy of the total cross section .The Large Hadron Collider (LHC) at CERN in Geneva has already delivered collisions with an energy never reached in a particle accelerator. The energy in the center of mass was 7 TeV (2010 – 2011) or 8 TeV (2012) and will ultimately reached 14 TeV in the near future. Thus, this will provide a good environment for a new precise measurement of the total pp cross section at this energy.The ATLAS detector installed in one of the four LHC interaction points is used to collect the result of the pp collisions. Its sub-detector ALFA located 240 m from the interaction point, is used to track protons resulting from elastic collisions.Therefore, within special beam optics conditions, ALFA is able to measure the total cross section and the nuclear slope. During this PhD the analysis performed on the first data led to σtot = 94.88 ± 0.12 stat ± 1.56syst mb and b = 19.45 ± 0.05stat ± 0.31syst GeV-2 at 7 TeV.