This thesis describes a new approach to the study of high-redshift star-formation and its environments that can be applied to large high-redshift surveys. Instead of relying on spectroscopy or narrow-band photometry to study galaxy line emission in detail, the properties of large emission line galaxy (ELG)populations are estimated from broadband photometry by measuring colour-residuals against colours drawn from a set of line-free stochastic burst models-based on (Bruzual & Charlot, 2003). Simulated star-formation histories drawn from semi-analytic and adaptive-mesh-refinement codes were converted into mock galaxy colours, but neither could-span the range of observed galaxy colours at high redshift. Instead, an existing set of exponentially declining star-formation models with stochastic bursts was used, because it closely spanned the range in observed galaxy colours in the bandsthat were line-free at each redshift. Small colour offsets were measured between the models and the observations, corresponding to the equivalent widths (EWs)of Hα, [OIII] and [OII]. In this way, I measure the rest-frame Equivalent Widths of the Hα, [OIII]and [OII] emission lines as they are redshifted through all filters from CANDELS(near-continuous U to 4.5μm coverage) for a large sample of galaxies from z=0.1up to z=5. This approach relies solely on the line-free models, a set of existing reliable photometric redshifts, and a colour cut (B−K < 2 or equivalent) to select only the dust-free young objects (the majority of identified emission-line galaxies). Once correctly identified, I apply this method to the CANDELS-UDS photometry to characterise the properties of Emission-Line Galaxies (ELGs) through these lines. I find that in this sample the Hα and [OIII] ELG fraction with EW > 150Årises from < 5% at z < 1 up to 40% at z > 2. The co-moving ELG density rises from 5 to 30 ×10 −4 /Mpc −3 at z=2.3. The evolution of median Hα EW with redshift is consistent with results from HiZELS and 3D-HST yielding median EW ∼ M 0.25 (1+z) 1.75 up to z=2.3, from which it departs to values of 450Å atz=4.3. [OIII] remains weaker than Hα for z < 3 and matches its values above that redshift. [OIII] also displays a larger fraction of extreme EWs than Hα. [OII], while correctly identified, never becomes as extreme as the other two lines lines, even when corrected for the evolving continuum. This is evidence of an increasing [OIII]/[OII] ratio with increasing z through-out this sample. While these results agree with spectroscopic and narrow-band surveys, the use of the deeper broadband filter coverage enables a systematic measurement of the increasingly prevalent high EWs ( > 500Å) in galaxies at every redshift spanning the 10 8 to 10 10.5 M range. Subsequently, this method was applied to all the other CANDELS fields (GOODS-South and North, COSMOS and EGS) and further corroborates these results. These results further show that EW dependence on mass is steeper for [OIII] than for Hα. Line EWs are then converted into luminosities for the three lines and fitting formulas are obtained, displaying L Hα ∼(1+z) 3.2 M 0.45−0.6log(1+z), with similar results for the other lines. L Hα is converted into star-formation rate and specific star-formation rate (sSFR). sSFR at low-z aligns approximately with the main sequence (with a steeper dependence in mass), but at high-redshift sSFR remains above the main sequence by a factor of 2 and rising towards medians SFR=100/Gyr around log(M/M )=9, showing a departure of the main sequence of star formation at lower masses log(M/M ) < 9.5. The SFRD of ELGs is 1% at low redshift, but rises to 30% at z=4.5. The L [OIII] /L Hα ratio is used to estimate L [OIII] /L Hβ and the ionization parameter q, for which the median atz > 0.5 stays approximately constant at 10 8 cm/s, and increases with mass. Using the L [OIII] /L [OII] ratio and q, median metallicity is shown to be sub-solar, and can be tentatively estimated for z > 0.5 to be Z/Z ∼0.3. The errors are large, but this could also mean a large range in metallicity from Z to 0.1Z . L [OIII] /L [OII] rises with sSFR as shown in the literature. This method shows great potential to survey emission-line-derived physical quantities for large galaxy populations with a low computational footprint, which could be particularly useful for pixel-by-pixel EW imaging. It is also flexibile, which allows it to be applied to any future deep multi-broadband fields.

Orientadores: Jacobus Willibrordus Swart, Pierre Kaufmann / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-22T19:46:53Z (GMT). No. of bitstreams: 1 Fernandes_LuisOlavodeToledo_M.pdf: 8033391 bytes, checksum: 7b7a925bf8a485ca4f76b7c8380299b3 (MD5) Previous issue date: 2013 / Resumo: O telescópio solar submilimétrico operando nas freqüências de 212 e 405 GHz detectou uma nova componente espectral das emissões de explosões solares, com máximo em algum ponto da faixa Terahertz, simultaneamente com a conhecida componente espectral em microondas, trazendo sérios desafios para interpretação. O diagnostico deste tipo de emissão transiente em freqüências THz traz desafios tecnológicos que são objetivo deste estudo. Este projeto consiste em um estudo das características de filtros e sensores não refrigerados para aplicação em projeto aeroespacial na faixa Terahertz do espectro eletromagnético. Foram estudados e caracterizados detectores bolométrico, piroeletrico, e optoacustico, precedidos por filtros passa-baixa que suprimem a radiação na faixa do visível e infravermelho próximo do espectro eletromagnético, filtros passa-banda centrados na freqüência THz desejada, e modulador mecânico. O detector a célula de Golay mostrou ser o mais sensível. Foi selecionado para o protótipo de fotômetro THz que serviu para definir parâmetros de projeto para o modelo de vôo, para observação solar fora da atmosfera terrestre, em balões estratosféricos, satélites, ou estações no solo com atmosfera excepcionalmente transparente. O sistema foi concebido para observar todo o disco solar e detectar pequenas variações relativas de temperatura causadas por explosões em regiões especifica do Sol. Obteve-se mínima detectabilidade de variações relativas de temperatura da ordem de 1 K com resolução temporal de subsegundo / Abstract: The solar submillimeter-wave telescope, operating at 212 and 405 GHz frequencies detected a new flare spectral component emission, peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constrains for interpretation. The diagnostics of this kind of transient emission at THz frequencies also bring technical challenges, which are the subject of this study. The project consists in a study of the characteristics of filters and uncooled detectors for aerospace project application at THz range of the electromagnetic spectrum. Three types of uncooled sensors were tested: bolometric, pyroelectric, and optoacoustic, proceeded by low-pass filters to suppress the visible and infrared radiation, band-pass filter centered at THz frequency, and a chopper. The Golay cell sensor was considered the most sensible detector of all, and was selected for the photometer prototype THz system to observe the Sun outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The system was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions of the Sun. The minimum relative temperature variation detected was about 1 K with subsecond time resolution / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

This thesis describes the application of tilting-filter photometry to the study of the airglow and aurora. Previous South African photometric research is reviewed. Optical instrumentation and techniques used in airglow and auroral research are reviewed. The transmission characteristics of narrowband interference filters are discussed. The analogue meridian-scanning tilting-filter photometry system used at Sanae, Antarctica is described. Shortcomings of this system have been identified, and modifications have been made to improve its spatial and temporal resolution. Details are given of the computer-controlled digital photometry system which replaced the analogue system. Equations are derived for the conversion of raw photometric data (analogue chart deflections or digital photon counts) to absolute emission intensities. The accuracy of the intensities obtained depends on the absolute calibration of the photometer, the transmission characteristics of the filter used to isolate the spectral feature of interest, and the effects of atmospheric extinction and scattering. The influence of these factors on observed emission intensities is discussed. Various models used to determine atmospheric correction factors are reviewed. It is shown that atmospheric correction factors can have a significant effect on both emission intensities and intensity ratios. The procedure used to determine the transmission characteristics of interference filters is described, as is the procedure used to cross-calibrate secondary light sources. The transmission characteristics of the filters and the brightnesses of the light sources were both found to have changed appreciably with age. The observation of a magnetospheric substorm at Sanae (L ≃ 4) is used to illustrate the use of a meridian-scanning tilting-filter photometer system in auroral research. The ratio I(557.7)/ I(391.4) observed at Sanae was found to be lower than expected, as were the OJ airglow emission intensities. A prototype digital photometer system was used aboard a ship, to observe the airglow in the region of the South Atlantic Anomaly. Significant N₂⁺ lNG emissions at 391.4 nm were measured, confirming the presence of discernable particle precipitation in the region. The 0I557.7 and 630.0 nm intensities measured from the ship were found to be lower than expected. This, combined with low airglow and auroral intensities measured at Sanae, is a cause for concern. It is recommended that further checks be made regarding the brightness of the calibration sources.

Context. The reionization of the Universe is one of the most important topics of present-day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H I ionizing background at z greater than or similar to 3. Aims. We measure the Lyman continuum escape fraction, which is one of the key parameters used to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at lambda <= 912 angstrom rest-frame and those that are able to reach the inter-galactic medium, i.e. that are not absorbed by the neutral hydrogen or by the dust of the galaxy's inter-stellar medium. Methods. We used ultra-deep U-band imaging (U = 30.2 mag at 1 sigma) from Large Binocular Camera at the Large Binocular Telescope (LBC/LBT) in the CANDELS/GOODS-North field and deep imaging in the COSMOS and EGS fields in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 <= z <= 3.40 to faint magnitude limits (L = 0.2L*, or equivalently M-1500 similar to -19). The narrow redshift range implies that the LBC U-band filter exclusively samples the lambda <= 912 angstrom rest-frame wavelengths. Results. We measured through stacks a stringent upper limit (<1.7% at 1 sigma) for the relative escape fraction of H I ionizing photons from bright galaxies (L > L*), while for the faint population (L = 0.2L*) the limit to the escape fraction is less than or similar to 10%. We computed the contribution of star-forming galaxies to the observed UV background at z similar to 3 and find that it is not sufficient to keep the Universe ionized at these redshifts unless their escape fraction increases significantly (>= 10%) at low luminosities (M-1500 >= -19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature, and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental in order to measure the Lyman continuum escape fraction down to faint magnitudes (M-1500 similar to -16) that are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.

Abstract The discs in galaxies are radially extended, rotationally supported, flattened systems. In the cosmological Lambda Cold Dark Matter model the formation of the discs is intimately connected with galaxy formation. Generally it is assumed that the discs have exponentially decreasing stellar surface brightness profiles, but completely satisfactory theoretical explanation for this has not been presented. Large number of studies in the past decade have challenged this view, and have found a change in the slope of the surface brightness profile in the outer regions of many galaxies discs: the surface brightness can decrease more, or less, steeply than in the inner regions. The transition between the two slopes is often called a disc break. Consequently, the discs are divided in three major categories: single exponential Type I, down-bending break Type II, and up-bending break Type III. Formation of these break features has been linked to the initial formation of the discs, internal evolution, and also with the interactions between galaxies. By studying the detailed properties of the disc break features, the evolutionary history of discs, and galaxies in general, can be better understood. The thesis work focuses on the structural analysis of the galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G), which consists of 2352 galaxies observed in the 3.6 and 4.5 µm mid-infrared wavelengths with the Spitzer space telescope. Work has been carried out as a part of the data-analysis pipelines of the S4G survey, utilizing surface photometry. In addition, special emphasis has been put on the study of the disc and disc break properties in a wide range of galaxy morphological types and stellar masses. The thesis work attempts to at least partially understand how galaxy stellar mass and observed wavelength affect the properties of the discs and breaks, and how galaxy structural components are connected with the breaks. The data comprises mainly of the 3.6 µm infrared data, providing a view to the stellar mass distribution of galaxies. We find that the Type II breaks are the most common disc profile type, found in 45 ± 2% of the sample galaxies, consisting of 759 galaxies in the stellar mass range 8.5 ≲ log10(M*/M⊙) ≲ 11. Type I discs are found in 31 ± 2%, and the Type III breaks in 23 ± 2% of the sample. The fraction of the profile types also depends of the galaxy stellar mass: fractions of the Types II and III increase, while Type I fraction decreases, with increasing stellar mass. We attribute these changes with stellar mass to the increased frequency of bar resonance structures in higher mass galaxies, which are commonly associated with a Type II break, and to the increased fraction of Type III profiles in generally more massive early-type disc galaxies. In addition to the Type II breaks associated with bar resonance structures, we find that nearly half of these breaks relate to the visual spiral outer edge, confirming previous results of the Type II break connection with galaxy structure, and thus the internal evolution rather than initial formation of discs. Complementary data in optical wavelengths from the Sloan Digital Sky Survey shows a strong change in the properties of the discs inside the Type II breaks, indicating that the inner discs are evolving via star formation. In late-type spiral galaxies (T ≳ 4) with a Type II break, possible evidence of radial stellar migration is found in the outer disc: the slope of the surface brightness profile is shallower in the infrared compared to optical wavelengths, indicating that older stellar populations are more evenly spread throughout the disc. Formation of the Type I and III profiles remain poorly understood. However, indication that some of the Type III profiles are formed by environmentally driven processes is found, with a correlation between the properties of the local environment and the disc profile parameters. Furthermore, indication of star formation possibly causing the up-bends in spiral galaxies is found through a presence of young stellar population in the outer disc section.

>Magister Scientiae - MSc / We investigate the link between environment and radiative accretion efficiency using a sample of 8946 radio-loud AGN detected at 1 − 2 GHz in the SDSS Stripe 82 region. We quantify their environments using the surface-density parameter, ƩN, which measures galaxy density based on distances to Nth nearest neighbours. Comparing Ʃ2 and Ʃ5 between AGN and control galaxies, we obtain relative densities that quantify the degree of galaxy clustering around each AGN. Using this, we examine the relation between density and the HERG-LERG dichotomy (accretion-modes) classified using a 1.4 GHz luminosity (L1.4GHz) threshold. Our results indicate that, in the low-redshift interval (0.1 < z < 0.2), LERGs occupy environments denser than the field. At intermediate redshifts (0.2 < z < 1.2), both LERGs and HERGs occupy regions denser than the field. Spearman’s rank tests show that correlations between density and L1.4GHz in both redshift intervals are weak. We conclude that the absence of a strong correlation is confirmation of the idea that galaxy density plays a more secondary role on AGN activity and also, accretion-mode classification (both measured using L1.4GHz). It is likely that the rate of gas accretion or properties of galactic-scale magnetic fields correlate more strongly with L1.4GHz, hence being primarily influential. / National Research Foundation (NRF)

Imaging with the James Webb Space Telescope (JWST) will allow observations of the bulk of distant galaxies at the epoch of reionization. The recovery of their properties, such as age, color excess E(B-V), specific star formation rate (sSFR), and stellar mass, will mostly rely on spectral energy distribution fitting, based on the data provided by JWST's two imager cameras, namely the Near Infrared Camera (NIRCam) and the Mid Infrared Imager (MIRI). In this work we analyze the effect of choosing different combinations of NIRCam and MIRI broadband filters, from 0.6 to 7.7 mu m, on the recovery of these galaxy properties. We performed our tests on a sample of 1542 simulated galaxies, with known input properties, at z = 7-10. We found that, with only eight NIRCam broadbands, we can recover the galaxy age within 0.1 Gyr and the color excess within 0.06 mag for 70% of the galaxies. Additionally, the stellar masses and sSFR are recovered within 0.2 and 0.3 dex, respectively, at z = 7-9. Instead, at z = 10, no NIRCam band traces purely the lambda > 4000 angstrom regime and the percentage of outliers in stellar mass (sSFR) increases by > 20% (> 90%), in comparison to z = 9. The MIRI F560W and F770W bands are crucial to improve the stellar mass and the sSFR estimation at z = 10. When nebular emission lines are present, deriving correct galaxy properties is challenging at any redshift and with any band combination. In particular, the stellar mass is systematically overestimated in up to 0.3 dex on average with NIRCam data alone and including MIRI observations only marginally improves the estimation.

Les astéroïdes binaires représentent un laboratoire naturel pour recueillir des informations cruciales sur les petits corps du Système Solaire, fournissant un aperçu des mécanismes de formation et d’évolution de ces objets. Leur caractérisation physique nous aide à comprendre les processus qui ont pris part à la formation et l’évolution des planétésimaux dans le Système Solaire. Les caractéristiques qui sont évaluées dans ce travail sont : la masse, la taille, la forme, la rotation, la densité, la composition et la taxonomie. L’une des plus importantes caractéristiques que l’on puisse obtenir avec les objets binaires -si le système peut être angulairement résolu- est leur masse grâce à l’interaction gravitationnelle mutuelle. Avec la masse et la taille du corps, nous pouvons déterminer sa densité, qui peut nous donner un aperçu de sa structure interne.A cet effet, l’exploration de données a été faite à partir d’images à haute résolution angulaire du télescope spatial Hubble et les télescopes au sol avec optique adaptative (VLT/NACO, VLT/SPHERE, Gemini/NIRI, Keck/NIRC2) dans le visible et proche infrarouge. Ayant réduit les images et mesuré les positions des satellites à de nombreuses époques, l’algorithme génétique Genoid est utilisé pour déterminer l’orbite de compagnons et la masse du corps central. Ceci est utile pour améliorer les éphémérides des satellites des binaires, qui à leur tour seront utiles pour prédire des occultations stellaires pour les futures campagnes d’occultation ; la technique d’occultation étant la plus fructueuse pour l’observation des objets de faible diamètre du Système Solaire. En ce qui concerne la taille et la détermination de la forme, l’algorithme KOALA d’inversion multidonnées est utilisé. En ce qui concerne la photométrie, courbes de lumière et couleurs SDSS ont été obtenues depuis le télescope de 1m au Pic du Midi et de 1.20 m de l’observatoire de Haute Provence dans le but de déterminer et affiner leurs propriétés. J’ai également acquis à distance des spectres d’astéroïdes binaires en utilisant le spectrographe Spex sur le télescope IRTF de 3m au Mauna Kea (Hawaii), afin de déterminer leur classe taxonomique pour la première fois. De plus, j’ai fait le modélisation de spectres de binaires sans taxonomie dans la base de données du SMASS collaboration. Ce plus grand échantillon, que j’ai comparé avec la population du NEAs et de Mars Crossers, en trouvant une prédominance dans le taxonomie Q/S. Cela est consistant avec la formation de binaires petits par effet YORP et perturbation rotationnelle. Finalement, j’ai développé une classification taxonomique générale, basée sur la photométrie large bande dans l’infrarouge, et je l’ai appliquée aux données de 30,000 astéroïdes provenant du survey VHS conduit par le télescope VISTA de l’ESO. / Binary asteroids represent a natural laboratory to gather crucial information on small bodiesof the Solar System, providing an overview of the formation and evolution mechanisms of these objects. Their physical characterization can constrain the processes that took part in the formation and evolution of planetessimals in the Solar System. The characteristics assessed in this work are: mass, size, shape, spin, density, surface composition, and taxonomy.One of the most important characteristics that can be obtained of binaries -if the system can be resolved- is their mass through their mutual gravitational interaction. From the mass and the size of the asteroid we determine its density, which provides insight on its internal structure.For this purpose, data mining has been done for high-angular resolution images from HST and ground-based telescopes equipped with adaptive optics (VLT/NACO, VLT/SPHERE, Gemini/NIRI, Keck/NIRC2) in the visible and near infrared. Having reduced the images and determined the satellite positions for over many epochs, the genetic algorithm Genoid algorithm is used to determine the orbit of the companion, and mass of the primary. This improves the ephemerides of binary companions, which in turn allows to stellar occultations by asteroids for future occultation campaigns.The occultation technique is the most fruitfulfor observing small diameter Solar System objects. As for the size and shape determination, KOALA multidata inversion algorithm is used.Concerning photometry, light curves and SDSS colors have been obtained for binary asteroids from T1M at Pic du Midi & 1.20m telescope at Haute Provence Observatory, aiming at determining and refining their properties. I remotely acquired spectra of binary asteroids using Spex/IRTF system based on 3m at Mauna Kea (Hawaii), to determine their taxonomic class for the first time. Additionally, I collected spectra of small binaries from the SMASS collaborationdatabase, modelled it, and found their taxonomy. I compare the now larger sample of classified binaries to the population of NEAs and Mars Crossers, and found a predominance of Q/S types. This is in agreement with a formation by YORP spin-up and rotational disruption.Finally, I developed a taxonomic classification for asteroids in general, based on infrared large band photometry, and applied it to 30,000 asteroids from VHS survey at the ESO’s telescope VISTA.

Astronomy is a data heavy field driven by observations of remote sources reflecting or emitting light. These signals are transient in nature, which makes it very important to fully utilize every observation. This however is often difficult due to the faintness of these observations, often are only slightly above the level of observational noise. We present new or adapted methodologies for dealing with these low signal-to-noise scenarios, along with practical examples including determining exoplanet physical properties, periodicities in asteroids, and the rotational and orbital properties of the multiple asteroid system 2577 Litva.

Multi-wavelength transit and secondary-eclipse light-curve observations are some of the most powerful techniques to probe the thermo-chemical properties of exoplanets. Although the large planet-to-star brightness contrast and few available spectral bands produce data with low signal-to-noise ratios, a Bayesian approach can robustly reveal what constraints we can set, without over-interpreting the data. Here I performed an end-to-end analysis of transiting exoplanet data. I analyzed space-telescope data for three planets to characterize their atmospheres and refine their orbits, investigated correlated noise estimators, and contributed to the development of the respective data-analysis pipelines. Chapters 2 and 3 describe the Photometry for Orbits, Eclipses and Transits (POET) pipeline to model Spitzer Space Telescope light curves. I analyzed secondary-eclipse observations of the Jupiter-sized planets WASP-8b and TrES-1, determining their day-side thermal emission in the infrared spectrum. The emission data of WASP-8b indicated no thermal inversion, and an anomalously high 3.6 micron brightness. Standard solar-abundance models, with or without a thermal inversion, can fit the thermal emission from TrES-1 well. Chapter 4 describes the most commonly used correlated-noise estimators for exoplanet light-curve modeling, and assesses their applicability and limitations to estimate parameters uncertainties. I show that the residual-permutation method is unsound for estimating parameter uncertainties. The time-averaging and the wavelet-based likelihood methods improve the uncertainty estimations, being within 20 - 50% of the expected value. Chapter 5 describes the open-source Bayesian Atmospheric Radiative Transfer (BART) code to characterize exoplanet atmospheres. BART combines a thermochemical-equilibrium code, a one-dimensional line-by-line radiative-transfer code, and the Multi-core Markov-chain Monte Carlo statistical module to constrains the atmospheric temperature and chemical-abundance profiles of exoplanets. I applied the BART code to the Hubble and Spitzer Space Telescope transit observations of the Neptune-sized planet HAT-P-11b. BART finds an atmosphere enhanced in heavy elements, constraining the water abundance to ~100 times that of the solar abundance.