We study the properties of the foreground galaxy of the Ruby, the brightest gravitationally lensed high-redshift galaxy on the sub-millimeter sky as probed by the Planck satellite, and part of our sample of Planck's dusty GEMS. The Ruby consists of an Einstein ring of 1.4" diameter at z = 3.005 observed with ALMA at 0.1" resolution, centered on a faint, red, massive lensing galaxy seen with HST/WFC3, which itself has an exceptionally high redshift, z = 1.525 +/- 0.001, as confirmed with VLT/X-shooter spectroscopy. Here we focus on the properties of the lens and the lensing model obtained with LENSTOOL. The rest-frame optical morphology of this system is strongly dominated by the lens, while the Ruby itself is highly obscured, and contributes less than 10% to the photometry out to the K band. The foreground galaxy has a lensing mass of (3.70 +/- 0.35) x 10(11) M-Theta Magnification factors are between 7 and 38 for individual clumps forming two image families along the Einstein ring. We present a decomposition of the foreground and background sources in the WFC3 images, and stellar population synthesis modeling with a range of star-formation histories for Chabrier and Salpeter initial mass functions (IMFs). Only the stellar mass range obtained with the latter agrees well with the lensing mass. This is consistent with the bottom-heavy IMFs of massive high-redshift galaxies expected from detailed studies of the stellar masses and mass profiles of their low-redshift descendants, and from models of turbulent gas fragmentation. This may be the first direct constraint on the IMF in a lens at z = 1.5, which is not a cluster central galaxy.

This thesis addresses the challenge of understanding the typical star formation histories of red sequence galaxies, using linestrength indices, mass-to-light ratios and redshift evolution as complementary constraints on their stellar age distribution. We first construct simple parametric models of the star formation history that bracket a range of scenarios, and fit these models to the linestrength indices of low-redshift cluster red-sequence galaxies. For giant galaxies, we con firm the downsizing trend, i.e. the stellar populations are younger, on average, for lower σ galaxies. We find, however, that this trend flattens or reverses at σ < 70km/s. We then compare predicted stellar mass-to-light ratios with dynamical mass-to-light ratios derived from the Fundamental Plane, or by the SAURON group. For galaxies with σ ~ 70 km/s, models with a late 'frosting' of young stars and models with exponential star formation histories have stellar mass-to-light ratios that are larger than observed dynamical mass-to-light ratios by factors of 1.7 and 1.4, respectively, and so are rejected. The single stellar population (SSP) model is consistent with the Fundamental Plane, and requires a modest amount of dark matter (between 20% to 30%) to account for the difference between stellar and dynamical mass-to-light ratios. A model in which star formation was 'quenched' at intermediate ages is also consistent with the observations, although in this case less dark matter is required for low mass galaxies. We also find that the contribution of stellar populations to the 'tilt' of the Fundamental Plane is highly dependent on the assumed star-formation history: for the SSP model, the tilt of the FP is driven primarily by stellar-population effects. For a quenched model, two-thirds of the tilt is due to stellar populations and only one third is due to dark matter or non-homology. Comparing to high redshift cluster data, we find again the SSP and quenched models, as well as a model where strangulation begins at intermediate ages after a period of constant star formation, are preferred. They predict the recent faint-end build up of the red sequence, along with observed dwarf-to-giant ratios. Only the SSP model appears to predict the observed M/L evolution, but only if selection effects are carefully modeled.

This thesis addresses the challenge of understanding the typical star formation histories of red sequence galaxies, using linestrength indices, mass-to-light ratios and redshift evolution as complementary constraints on their stellar age distribution. We first construct simple parametric models of the star formation history that bracket a range of scenarios, and fit these models to the linestrength indices of low-redshift cluster red-sequence galaxies. For giant galaxies, we con firm the downsizing trend, i.e. the stellar populations are younger, on average, for lower σ galaxies. We find, however, that this trend flattens or reverses at σ < 70km/s. We then compare predicted stellar mass-to-light ratios with dynamical mass-to-light ratios derived from the Fundamental Plane, or by the SAURON group. For galaxies with σ ~ 70 km/s, models with a late 'frosting' of young stars and models with exponential star formation histories have stellar mass-to-light ratios that are larger than observed dynamical mass-to-light ratios by factors of 1.7 and 1.4, respectively, and so are rejected. The single stellar population (SSP) model is consistent with the Fundamental Plane, and requires a modest amount of dark matter (between 20% to 30%) to account for the difference between stellar and dynamical mass-to-light ratios. A model in which star formation was 'quenched' at intermediate ages is also consistent with the observations, although in this case less dark matter is required for low mass galaxies. We also find that the contribution of stellar populations to the 'tilt' of the Fundamental Plane is highly dependent on the assumed star-formation history: for the SSP model, the tilt of the FP is driven primarily by stellar-population effects. For a quenched model, two-thirds of the tilt is due to stellar populations and only one third is due to dark matter or non-homology. Comparing to high redshift cluster data, we find again the SSP and quenched models, as well as a model where strangulation begins at intermediate ages after a period of constant star formation, are preferred. They predict the recent faint-end build up of the red sequence, along with observed dwarf-to-giant ratios. Only the SSP model appears to predict the observed M/L evolution, but only if selection effects are carefully modeled.

Using a combination of optical and near-infrared photometry, we have studied both the resolved and integrated stellar populations for a sample of Virgo cluster galaxies spanning the full range of galaxian parameters. The derived stellar population properties are compared against galaxy structural and environmental measures to gauge the importance of these factors in establishing galaxy star formation histories and chemical evolution. Although galaxy colours do not uniquely probe a galaxy's star formation history, meaningful results may be obtained if considered in a relative sense. We find that colour profiles reflect variations in both stellar age and metallicity within galaxies. We also uncover systematic variations in colour gradients, and thus age/metallicity gradients, along the Hubble sequence, such that age and metallicity gradients become increasingly negative toward later Hubble types. However, only weak correlations exist between galaxies' stellar populations and their structure and environment. The correlations we find suggest that the star formation histories of gas-rich galaxies are strongly influenced by gas removal within the cluster, while their chemical evolution is due to a combination of stellar mass-dependent enrichment and outflow retention. The assembly of gas-poor giant galaxies is consistent with a hierarchical scenario wherein gas-rich mergers dominate by number. Gas-poor dwarfs differ from the giants, however, appearing as the product of environmentally-driven evolution. Spiral galaxies bridge the dwarf-giant gap, whereby merging and gas-stripping signatures are imprinted in their stars. Early-type spirals seem to have fallen into the cluster sooner than the later types, thereby ceasing star formation in their disks at earlier epochs. The bulges of both types, however, appear to have grown via merging. The nature of this merging (minor versus major) remains unknown. Irregular galaxies exhibit signs of a recent gravitational encounter that has redistributed both their stars and gas, the latter of which caused recent star formation. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-08-25 14:12:46.48

Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica. / We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.

Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica. / We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.

abstract: Understanding the properties and formation histories of individual stars in galaxies remains one of the most important areas in astrophysics. The impact of the Hubble Space Telescope<\italic> (HST<\italic>) has been revolutionary, providing deep observations of nearby galaxies at high resolution and unprecedented sensitivity over a wavelength range from near-ultraviolet to near-infrared. In this study, I use deep HST<\italic> imaging observations of three nearby star-forming galaxies (M83, NGC 4214, and CGCG 269-049) based on the HST<\italic> observations, in order to provide to construct color-magnitude and color-color diagrams of their resolved stellar populations. First, I select 50 regions in the spiral arm and inter-arm areas of M83, and determine the age distribution of the luminous stellar populations in each region. I developed an innovative method of star-by-star correction for internal extinction to improve stellar age and mass estimates. I compare the extinction-corrected ages of the 50 regions with those determined from several independent methods. The young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with a scenario where star formation is associated with the spiral arms, and stars form primarily in star clusters before dispersing on short timescales to form the field population. I address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected. The same procedure is applied to nearby starbursting dwarf NGC 4214 to study the distributions of young and old stellar populations. Lastly, I describe the analysis of the HST<\italic> and Spitzer Space Telescope<\italic> observations of the extremely metal-poor dwarf galaxy (XMPG) CGCG 269-049 at a distance of 4.96 Mpc. This galaxy is one of the most metal-poor known with 12+log(O/H)=7.43. I find clear evidence for the presence of an old stellar population in CGCG~269-049, ruling out the possibility that this galaxy is forming its first generation of stars, as originally proposed for XMPGs. This comprehensive study of resolved stellar populations in three nearby galaxies provides detailed view of the current state of star formation and evolution of galaxies. / Dissertation/Thesis / Ph.D. Astrophysics 2012

The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half million high-resolution (R similar to 22,500), high signal-to-noise ratio (>100), infrared (1.51-1.70 mu m) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This paper describes the motivations for the survey and its overall design-hardware, field placement, target selection, operations-and gives an overview of these aspects as well as the data reduction, analysis, and products. An index is also given to the complement of technical papers that describe various critical survey components in detail. Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the APOGEE data products are publicly available.

Here, we present the results from our analysis of 6 yr of optical photometry taken by the Siding Spring Survey (SSS). This completes a search for periodic variable stars within the 30 000 deg(2) of the sky covered by the Catalina Surveys. The current analysis covers 81 million sources with declinations between -20 degrees. and -75 degrees. with median magnitudes in the range 11 < V < 19.5. We find approximately 34 000 new periodic variable stars in addition to the similar to 9000 RR Lyrae that we previously discovered in SSS data. This brings the total number of periodic variables identified in Catalina data to similar to 110 000. The new SSS periodic variable stars mainly consist of eclipsing binaries, RR Lyrae, LPVs, RS CVn stars, delta Scutis, and Anomalous Cepheids. By cross-matching these variable stars with those from prior surveys, we find that similar to 90 per cent of the sources are new discoveries and recover similar to 95 per cent of the known periodic variables in the survey region. For the known sources, we find excellent agreement between our catalogue and prior values of luminosity, period, and amplitude. However, we find many variable stars that had previously been misclassified. Examining the distribution of RR Lyrae, we find a population associated with the Large Magellanic Cloud (LMC) that extends more than 20 degrees from its centre confirming recent evidence for the existence of a very extended stellar halo in the LMC. By combining SSS photometry with Dark Energy Survey data, we identify additional LMC halo RR Lyrae, thus confirming the significance of the population.

Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica. / We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.