1,720,979 research outputs found
Photometric and spectroscopic tracers of the inside-out growth of massive galaxies
No full textThe most massive (Mstellar > 1011M_) galaxies of the Universe experience a dramatic evolution in their observational properties (size, morphology, kinematics, star formation rates) across cosmic time. This metamorphosis, which implies an accelerated evolution of this galaxy population in comparison with lower mass galaxies, is not well understood.
This thesis explores the structural properties and spectroscopic evolution of massive galaxies in the nearby Universe (z < 0:5) by conducting two different but complementary studies: one employing surface photometry using deep photometric data from the Hubble Space Telescope (HST), and another one exploiting spectral synthesis using state-of-the-art integral field spectroscopy (IFS) from MUSE.
The first study makes use of HST CANDELS data to analyze a sample of 17 nearby (z 1011M_) galaxies, with the aim to disentangle the structural components of these systems and study possible faint non-axissymmetric features. The excellent HST spatial resolution for intermediate redshift objects justifies a detailed structural analysis that combines two parametric components for the disk and bulge, instead of a purely automatic application of one single Sérsic model. Therefore careful single Sérsic fits and bulge-disk decompositions are performed to model the galaxy surface brightness profiles. The model color profiles are compared with the observed ones, and multi-component global effective radii are derived in order to obtain more accurate measurements of the size of galaxies and their position on the mass-size relation. It was found that the Sérsic index does not offer a good proxy for the visual morphology of our sample of massive galaxies. The derived multi-component effective radii offer a better description of the size of the sample galaxies than those inferred from single Sérsic models with GALFIT. The galaxies in our sample lie on the scatter of the local masssize relation, indicating that these massive objects have not experienced a significant growth in size since z ~ 0.5. Interestingly, the few outliers in the local mass-size relation are late-type galaxies, suggesting that spheroids must have reached the local mass-size relation earlier. For most of our sample, both single and multi-component Sérsic models retrieved with GALFIT show considerable systematic deviations from the observed surface brightness profiles in the galaxy peripheries that consequently propagate into significant uncertainties in the Sérsic fit parameters. In several cases they also indicate that colors inferred from Sersic fits show strong discrepancies from the observed colors.
The second study explores the build-up process of massive galaxies by examining IFS MUSE data. We conduct a direct comparison between the spatially resolved stellar populations of the largest galaxy known in the Universe – IC1101 – and four other nearby early-type massive galaxies (ETGs), which represent the predominant morphological massive class in the nearby Universe. The IFS data were spatially-binned using Voronoi tesselation and modeled with our in-house spectral fitting pipeline Porto3D, enabling us to study the galaxy stellar populations, and focusing on the stellar age and metallicity radial profiles and their corresponding gradients. It was found a diversity in the radial distribution of equivalent width (EW) of H α) supporting a subdivision of ETGs into two groups: type i and type ii ETGs. The ones classified as type ii ETGs show an outwardly increasing EW(H α) whereas type i show a nearly constant EW(Hα) with values being consistent with gas photoionization by post-AGB stellar populations. All but one of the analyzed galaxies show LINER-specific spectroscopic properties out to several kpc from their nucleus. Old stellar ages (above 9 Gyr) and negative radial gradients are found for all galaxies, supporting an inside-out formation scenario. Stellar metallicities are over-solar for all galaxies with only a single exception. The main difference in the comparison of IC1101 with the rest of the sample lies on its positive stellar metallicity gradient. This result is atypical for ETGs in the low-redshift Universe and may be an indication of different evolutionary mechanisms for this galaxy. We tentatively propose plausible scenarios to explain the metal-enriched periphery of IC1101, being (i) a contribution of metal-rich intra-cluster stellar
light, and (ii) a self-enrichment by “wet” mergers of accreted satellites that fed star formation.
We also conjecture that this might partly be an artifact created by the astonishing large velocity dispersion determined in the outskirts of IC1101
Photometric and spectroscopic tracers of the inside-out growth of massive galaxies
No full textThe most massive (Mstellar > 1011M_) galaxies of the Universe experience a dramatic evolution in their observational properties (size, morphology, kinematics, star formation rates) across cosmic time. This metamorphosis, which implies an accelerated evolution of this galaxy population in comparison with lower mass galaxies, is not well understood.
This thesis explores the structural properties and spectroscopic evolution of massive galaxies in the nearby Universe (z < 0:5) by conducting two different but complementary studies: one employing surface photometry using deep photometric data from the Hubble Space Telescope (HST), and another one exploiting spectral synthesis using state-of-the-art integral field spectroscopy (IFS) from MUSE.
The first study makes use of HST CANDELS data to analyze a sample of 17 nearby (z 1011M_) galaxies, with the aim to disentangle the structural components of these systems and study possible faint non-axissymmetric features. The excellent HST spatial resolution for intermediate redshift objects justifies a detailed structural analysis that combines two parametric components for the disk and bulge, instead of a purely automatic application of one single Sérsic model. Therefore careful single Sérsic fits and bulge-disk decompositions are performed to model the galaxy surface brightness profiles. The model color profiles are compared with the observed ones, and multi-component global effective radii are derived in order to obtain more accurate measurements of the size of galaxies and their position on the mass-size relation. It was found that the Sérsic index does not offer a good proxy for the visual morphology of our sample of massive galaxies. The derived multi-component effective radii offer a better description of the size of the sample galaxies than those inferred from single Sérsic models with GALFIT. The galaxies in our sample lie on the scatter of the local masssize relation, indicating that these massive objects have not experienced a significant growth in size since z ~ 0.5. Interestingly, the few outliers in the local mass-size relation are late-type galaxies, suggesting that spheroids must have reached the local mass-size relation earlier. For most of our sample, both single and multi-component Sérsic models retrieved with GALFIT show considerable systematic deviations from the observed surface brightness profiles in the galaxy peripheries that consequently propagate into significant uncertainties in the Sérsic fit parameters. In several cases they also indicate that colors inferred from Sersic fits show strong discrepancies from the observed colors.
The second study explores the build-up process of massive galaxies by examining IFS MUSE data. We conduct a direct comparison between the spatially resolved stellar populations of the largest galaxy known in the Universe – IC1101 – and four other nearby early-type massive galaxies (ETGs), which represent the predominant morphological massive class in the nearby Universe. The IFS data were spatially-binned using Voronoi tesselation and modeled with our in-house spectral fitting pipeline Porto3D, enabling us to study the galaxy stellar populations, and focusing on the stellar age and metallicity radial profiles and their corresponding gradients. It was found a diversity in the radial distribution of equivalent width (EW) of H α) supporting a subdivision of ETGs into two groups: type i and type ii ETGs. The ones classified as type ii ETGs show an outwardly increasing EW(H α) whereas type i show a nearly constant EW(Hα) with values being consistent with gas photoionization by post-AGB stellar populations. All but one of the analyzed galaxies show LINER-specific spectroscopic properties out to several kpc from their nucleus. Old stellar ages (above 9 Gyr) and negative radial gradients are found for all galaxies, supporting an inside-out formation scenario. Stellar metallicities are over-solar for all galaxies with only a single exception. The main difference in the comparison of IC1101 with the rest of the sample lies on its positive stellar metallicity gradient. This result is atypical for ETGs in the low-redshift Universe and may be an indication of different evolutionary mechanisms for this galaxy. We tentatively propose plausible scenarios to explain the metal-enriched periphery of IC1101, being (i) a contribution of metal-rich intra-cluster stellar
light, and (ii) a self-enrichment by “wet” mergers of accreted satellites that fed star formation.
We also conjecture that this might partly be an artifact created by the astonishing large velocity dispersion determined in the outskirts of IC1101
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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