1,720,960 research outputs found
Gas metallicities in galaxies
Full text linkTopics covered in this thesis mainly concern the study of gas metallicity in galaxies by measuring the emission lines produced by ionized gas, and the calculation of metallicity estimators as the ratio between them.
The first part of the thesis examines a sample of galaxies at intermediate redshift (z 0.4), through which we searched for a correlation between the metallicity indicators measurable on the integrated spectrum and photometric properties such as colors and magnitudes.
In the second part of the thesis we analyzed the radial profiles of the same gas metallicity indices for a class of galaxies not yet studied in great detail such as the low surface brightness galaxies.Gli argomenti trattati all’interno di questa tesi riguardano principalmente lo studio della metallicità del gas delle galassie attraverso la misura delle righe di emissione prodotte dal gas ionizzato, ed il calcolo di estimatori di metallicità ottenuti come rapporti tra queste.
La prima parte della tesi prende in esame un campione di galassie a redshift intermedio (z 0.4), tramite le quali si è cercata una correlazione tra gli indicatori di metallicità misurabili dallo spettro integrato ottenuto e proprietà fotometriche quali i colori e le magnitudini.
Nella seconda parte della tesi si analizza l’andamento radiale degli stessi indicatori di metallicità del gas per una classe di galassie non approfonditamente studiata quale è quella delle galassie di bassa brillanza superficiale
Kinematics of low surface brightness galaxies
No full textWe analyzed the kinematic of 12 low surface-brightness (LSB) galaxies to study the correlation between the disk circular velocity V_c and the central velocity dispersion of the spheroidal component σ_0. This relation has been claimed to be either the same power-law relation or a different linear one with respect to high surface-brightness (HSB) galaxies. We confirm here that LSB and HSB galaxies follow two different linear V_c-σ_0 relations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Kinematics of low surface-brightness galaxies
No full textIn order to verify the correlation between the disk circular velocity V_c and the central velocity dispersion of the spheroidal component sigma_c , we analyzed a sample of 12 low surface-brightness galaxies (LSBs). In previous works LSBs have been claimed to follow either a different linear or the same power-law relation with respect to high surface-brightness galaxies (HSBs). The galaxies studied in this work enable us to confirm that LSBs and HSBs follow two different linear V_c-sigma_c relations
Ultraviolet variability in the nucleus of the elliptical galaxy NGC 4278
No full textWe searched the HST Science Archive for the nuclei of elliptical galaxies with images obtained in different epochs, to detect the presence of far-ultraviolet variability. We found multi-epochs observations only for the elliptical galaxy NGC 4278. It hosts a barely resolved nuclear source which increased its UV flux by a factor 4 between June 1994 and January 1995. The properties of the UV flare of NGC 4278 are remarkably similar to the UV-bright nuclear transients discovered earlier in other low-luminosity AGNs. This supports the idea that UV flaring near the center of galaxies may be a common event and offers a way to search for black-hole-related activities in otherwise quiescent galaxies
Ultraviolet variability in the nucleus of the giant elliptical NGC 4278
No full textThe variability of the UV luminosity and mass of the supermassive black hole (SBH) in the nucleus of the giant elliptical NGC 4278 were derived by analyzing the UV images and Hα spectrum available in the Hubble Space Telescope Science Archive. The UV nuclear source in NGC 4278 is almost certainly associated to the low-luminosity AGN responsible for its known radio emission. The properties of this UV flare and SBH are remarkably similar to the UV-bright nuclear transients and SBHs discovered earlier in other low-luminosity AGNs. This supports the idea that UV flaring near the center of galaxies may be a common event and offers a way to search for SBH-related activities in otherwise quiescent galaxies
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
