1,720,970 research outputs found
Observational constraints to the stellar populations in the center of galactic spheroids
No full textGalactic spheroids represent one of the key challenges to our understanding of galaxies formation and evolution as far as their star-formation history is concerned. The knowledge of the stellar content of early-type galaxies is fundamental to understand their star formation and chemical evolution. The thesis is focused on two main topics, both concerned with the study of unresolved stellar populations in the centers of galaxies. The first one is a comprehensive study of the photometrical properties of three galaxies that belong to the Virgo Cluster and host Nuclear Stellar Disks (NSD) in their centers. The second one is focused on the study of absorption lines in the Near-infrared (NIR) that are strictly correlated with the properties of the stellar populations. I defined new NIR spectral indices that show great potential for a stellar population analysis. A simple SSP model is created to interpret the integrated NIR light. The development of the SSPs model pointed out at some limitations of the currently available stellar spectral libraries. Consequently, the study of metal poor red supergiant stars in the NIR was carried out.Gli sferoidi galattici rappresentano uno dei punti chiave per comprendere la formazione e l'evoluzione delle galassie, sopratutto per quanto riguarda la formazione stellare. Infatti, conoscere il contenuto stellare delle galassie early-type fornishe importanti indicazioni sulla formazione e l'evoluzione chimica delle loro stelle. Due sono gli argomenti trattati in questa tesi entrambi connessi con lo studio delle popolazione stellari non risolte nel centro delle galassie. Il primo studia dettagliatamente le proprietà fotometriche di tre galassie appartenenti all'ammasso della Vergine che ospitano un disco stellare nel loro nucleo. Il secondo mira ad individuare le righe spettrali fondamentali per lo studio delle popolazioni stellari nel vicino infrarosso (NIR). I nuovi indici spettrali definiti nel NIR hanno dimostrato essere notevolmente efficaci per l'analisi delle popolazioni stellari. Un semplice modello di popolazione stellare semplice (SSP) è stato creato per interpretare la luce integrata nel vicino infrarosso. Lo sviluppo del modello SSP ha messo in evidenza alcuni limiti delle librerie stellari spettrali oggigiorno disponibili. Pertanto è stato studiato lo spettro di alcune stelle supergiganti rosse a bassa metallicità nel NIR
Waste processing: New near infrared technologies for material identification and selection
No full textThe awareness of environmental issues on a global scale increases the opportunities for waste handling companies. Recovery is set to become all the more important in areas such as waste selection, minerals processing, electronic scrap, metal and plastic recycling, refuse and the food industry. Effective recycling relies on effective sorting. Sorting is a fundamental step of the waste disposal/recovery process. The big players in the sorting market are pushing for the development of new technologies to cope with literally any type of waste. The purpose of this tutorial is to gain an understanding of waste management, frameworks, strategies, and components that are current and emerging in the field. A particular focus is given to spectroscopic techniques that pertains the material selection process with a greater emphasis placed on the NIR technology for material identification. Three different studies that make use of NIR technology are shown, they are an example of some of the possible applications and the excellent results that can be achieved with this technique
WASTE IDENTIFICATION AND SELECTION BY MEANS OF HIPERSPECTRAL NIR TECHNOLOGY
No full textRecovered wood becomes more and more important for the production of wood-base panels. The increasing demand resulted in the need to improve the cleaning process of post-consumer material, eliminating in a more effective and efficient way plastic impurities. We have developed a new method that takes advantages of the NIR spectral images to identify different classes of materials present in wood waste. We have investigated the spectrum of a wide sample of materials as plastics, ceramics, tiles, woods, laminates in the range 1100 - 2500 nm. We found those features that characterized the different classes of materials and searched for those spectral regions able to distinguish them. We have studied the correlation among the various features that characterize the classes and the spectral bands potentially most effective in the discrimination process have been identified. We defined different indices able to distinguish among different materials. The developed classification method shows that the near infrared spectral analysis can be used as an efficient technique to identify different objects facilitating rapid and accurate separation process
WOOD RECYCLING BY NIR TECHNOLOGY
No full textThe recycling of waste wood has become increasingly important during the last few decades. The use of recovered wood varies among the countries and in Italy, the percentage of recovered wood used for particleboard production, reached the 89%. Anyway, to use recycled wood to produce MDF panels or energy we need to improve the cleaning process of post-consumer material, eliminating in a more effective and efficient way plastic impurities. We first studied in laboratory a wide sample of objects representative of wood garbage dump materials and we developed a new near infrared spectral method for materials identification and selection. We developed a pilot system for the automated online sorting of high volumes of waste wood to which we applied the new method. The material sorter is equipped with a Hyperspectral Imaging Spectroscopy (HIS) system, a conveyor and the processing system we tested. We present the approach and the first results of the identification and selection process
Near infrared technology for material identification and selection
No full textThe increasing demand for recycled wood to produce particleboard and MDF panels has resulted in the need to improve the cleaning process of post-consumer material, eliminating in a more effective and efficient way plastic impurities. We have developed a new method based on the NIR diffuse reflectance spectral analysis for the identification of different classes of materials that can be used in the selection process.
We have investigated the diffuse reflected light in the range 1100 - 2500 nm of a wide sample of materials including plastics, ceramics, tiles, woods and laminates as representative of garbage dump materials. We have considered the typical features of the different classes of materials and looked for those spectral regions that present some difference among the classes. We have studied the correlation among the various features characterizing the spectra of each class and identifying the spectral bands potentially most effective in the discrimination process. Accordingly, six indices able to distinguish different materials have been defined. The results show that the near infrared spectral analysis can be used as an efficient analytical technique to identify different objects facilitating rapid separation process
IC 5181: An S0 galaxy with ionized gas on polar orbits
No full textThe nearby S0 galaxy IC 5181 is studied to address the origin of the ionized gas component that orbits the galaxy on polar orbit. We perform detailed photometric and spectroscopic observations measuring the surface brightness distribution of the stars (I band), ionized gas of IC 5181 (Halpha narrow band), the ionized-gas and stellar kinematics along both the major and minor axis, and the corresponding line strengths of the Lick indices. We conclude that the galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. The result is suggesting that the gas component is not related to the stars having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment
The nature of nuclear stellar disks
No full textSmall and bright stellar disks with scalelengths of few tens of parsec are
known to reside in the center of galaxies. Despite the attention they received in the last years, the processes responsible of their formation are not completely understood and still under debate. Unveiling the formation processes of these structure is important since they constrain the formation and evolution of the host galaxy. Furthermore, nuclear stellar disks are among the smallest structures known to reside in the center of galaxies and together with black holes and nuclear clusters they are crucial to infer clues on the coevolution between the galaxy and its nucleus
Stellar populations of bulges in galaxies with a low surface-brightness disc
No full textThe radial profiles of the Hβ, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and α/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar α/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar
The external origin of the polar gaseous disk of the S0 galaxy IC 5181
No full textContext. Galaxies accrete material from the environment through acquisition and merging events. These processes contribute to galaxy assembly and leave their fingerprints on the galactic morphology, internal kinematics of gas and stars, and stellar populations.
Aims: We study the nearby S0 galaxy IC 5181 to address the origin of the ionized gas component that orbits the galaxy on polar orbits.
Methods: We measure the surface brightness distribution of the stars and ionized gas of IC 5181 from broadband and narrow-band imaging. The structural parameters of the galaxy are obtained with a photometric decomposition assuming a Sérsic and exponential profile for the bulge and disk, respectively. We measure the ionized-gas and stellar kinematics and the line strengths of the Lick indices of the stellar component along both the major and minor axis. The age, metallicity, and [α/Fe] enhancement of the stellar populations are derived using single stellar population models with variable element abundance ratios. The ionized-gas metallicity is obtained from the equivalent width of the emission lines.
Results: The galaxy IC 5181 is a morphologically undisturbed S0 galaxy with a classical bulge made by old stars with super solar metallicity and overabundance. Stellar age and metallicity decrease in the disk region. The galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk.
Conclusions: We interpret the kinematical decoupling as suggesting that there is a component of gas, which is not related to the stars and having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment
Stellar populations of bulges in galaxies with low surface-brightness discs
No full textThe radial profiles of the age, metallicity and α/Fe enhancement of the stellar populations in the bulge-dominated region for a sample of eight spiral galaxies with low surface-brightness stellar discs and bulges are presented. Almost all the sample bulges are characterised by young stellar populations, solar α/Fe enhancements and metallicities spanning from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas a negative metallicity gradient is found in a few cases. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies and are therefore likely to have common formation scenarios and evolution histories
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