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Groups of galaxies: a key environment for galaxy evolution
Get PDFGalaxy groups are the most common structure in the universe and, as they span a wide range in local density, showing properties which range from cluster-like to field-like represent the ideal place to investigate galaxy evolution. In particular, on these scales can be active fundamental pre-processes responsible of galaxy transformations; thus, they can have a profound effect on the overall galaxy population since about 50% of all galaxies are in groups by z ~ 0. The aim of the thesis has been to explore the properties of galaxies in groups and to understand whether and how they vary as function of global environment in which they reside. In this thesis I first present the construction and the characteristics of a new catalog of groups and galaxies representative of the general field population at low redshift, the Padova Millennium Galaxy and Group Catalogue (PM2GC). The group building method used to identify galaxy groups is based on a Friends-of-Friends algorithm which takes advantage of two available quantities in observational galaxy catalogs: the projected separation in the sky and the velocity difference in the redshift space. Non-group galaxies were subdivided into “binary” systems of two bright close companions, and “single” galaxies with no companion, in order to identify different environments useful scientific analysis. I compared galaxy groups properties with those of more isolated galaxies in other environments in PM2GC and with cluster galaxies from the WIde-field Nearby Galaxy cluster Survey (WINGS). I performed a morphological analysis studying the relation between morphology and mass among single, binaries, group and cluster galaxies. I found a very smooth trend of all morphological types with environment except for S0 galaxies in clusters. Moreover, I shown that the morphological fraction depends strongly on galaxy stellar mass at very high masses. Finally, I investigated the galaxy stellar mass function (MF) to understand if the observed variations in the galaxy morphology can be explained by the dependence of the galaxy mass itself on environment. I found that at low redshift, contrary to expectations, the mass function of general field is indistinguishable from that of galaxy clusters while the difference becomes evident only considering lowest mass haloes, i.e. single galaxies. I also found indication that there is a dependence of the upper mass limit of samples on environment with the most massive galaxies only hosted by the most massive haloes. All these results represent a very important indications that not only stellar mass but also the environment in which a galaxy resides play a role in galaxy evolution. Moreover, they highlight that exist a cluster specific effect which acts on the classes of spirals and S0s galaxies since a significant number of S0s in clusters has a different origin with respect to S0s in other environments. This means that S0 population in clusters probably are closely related to spiral oneI gruppi di galassie sono le strutture pi ù comuni nell’universo e, poiché abbracciano una vasta gamma di densità locali mostrando proprietà che si estendono da quelle tipiche degli ammassi a quelle tipiche del campo, rappresentano il luogo ideale per indagare l’evoluzione delle galassie. In particolare, i pre-processi responsabili delle trasformazioni delle galassie possono avvenire su queste scale; per tale motivo, essi possono avere un profondo effetto sulla popolazione complessiva di galassie in quanto pi ù del 50 per cento di tutte le galassie dell’universo oggi sono in gruppi. Lo scopo della tesi è stato quindi quello di esplorare le proprietà delle galassie nei gruppi e capire se e come esse variano in funzione dell’ambiente in cui risiedono. In questa tesi presento innanzitutto la costruzione e le caratteristiche di un nuovo catalogo di gruppi e di galassie rappresentativo della popalazione di campo a basso redshift, il Padova Millennium Galaxy and Group Catalog (PM2GC). Il metodo utilizzato per identificare i gruppi di galassie si basa sull’algoritmo ”Friends-of-Friends” che sfrutta due quantità disponibili nei cataloghi osservativi delle galassie: la separazione proiettata nel cielo e la differenza di velocità nello spazio dei redshift. Le galassie che non risultano essere membri dei gruppi sono state suddivise in galssie appartenenti a sistemi ”binari” costituiti da due oggetti vicini molto luminosi e galassie ”singole” senza alcun compagno, al fine di identificare diversi ambienti utili per l’analisi scientifica. Ho confrontato le proprietà delle galassie nei gruppi con quelle di galassie più isolate appartenenti ad altri ambienti nel catalogo PM2GC e con galassie di ammasso prese dalla WIde-field Nearby Galaxy cluster Survey (WINGS). Ho quindi eseguito un’analisi morfologica studiando la relazione tra morfologia e massa tra le galassie singole, binarie, di gruppo e di ammasso. Ho trovato un andamento molto regolare in funzione dell’ambiente per tutti i tipi morfologici fatta eccezione per le galassie S0 negli ammassi. Inoltre, ho mostrato che la frazione morfologica dipende fortemente dalla massa delle galassie soprattutto per masse molto grandi. Infine, ho esaminato la funzione di massa stellare delle galassie (MF) per capire se le variazioni che abbiamo osservato nelle proprietà morfologiche delle galassie possono essere spiegate dalla dipendenza della massa stessa della galassia dall’ambiente. Ho scoperto che a basso redshift, contrariamente alle aspettative, la funzione di massa delle galassie di campo è indistinguibile da quella degli ammassi di galassie e tale differenza diventa evidente solo considerando aloni con masse pi ù basse, vale a dire le galassie singole. Ho anche trovato indicazione che vi è una dipendenza del limite di massa superiore dei diversi campioni di galassie dall’ambiente con le galassie pi ù massicce che sono ospitate dagli aloni più massicci. Tutti questi risultati ci danno importanti indicazioni che non solo la massa stellare ma anche l’ambiente in cui esse risiedono gioca un ruolo nell’evoluzione delle galassie. Inoltre, essi evidenziano che esiste un effetto specifico degli ammassi di galassie che agisce esclusivamente sulle classi di galassie S0 e spirali poiché un numero significativo di galassie S0 negli ammassi ha un’origine diversa rispetto alle S0 in altri ambienti. Questo significa che probabilmente la popolazione di galassie S0 negli ammassi è strettamente collegata a quella delle spiral
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
The Evolution of the Number Density of Compact Galaxies
Get PDFWe compare the number density of compact (small size) massive galaxies at low and high redshift using our Padova Millennium Galaxy and Group Catalogue (PM2GC) at z = 0.03-0.11 and the CANDELS results from Barro et al. at z = 1-2. The number density of local compact galaxies with luminosity weighted (LW) ages compatible with being already passive at high redshift is compared with the density of compact passive galaxies observed at high-z. Our results place an upper limit of a factor ∼2 on the evolution of the number density and are inconsistent with a significant size evolution for most of the compact galaxies observed at high-z. Instead, the evolution may be significant (up to a factor five) for the most extreme, ultracompact galaxies. Considering all compact galaxies, regardless of LW age and star formation activity, a minority of local compact galaxies (≤1/3) might have formed at z < 1. Finally, we show that the secular decrease of the galaxy stellar mass due to simple stellar evolution may in some cases be a non-negligible factor in the context of the evolution of the mass-size relation, and we caution that passive evolution in mass should be taken into account when comparing samples at different redshifts. © 2013. The American Astronomical Society. All rights reserved
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