1,721,039 research outputs found
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Disentangling luminosity, morphology, star formation, stellar mass, and environment in galaxy evolution
No full textWe present a study of the photometric and spectroscopic properties of galaxies in a sample of six nearby, rich galaxy clusters. We examine the variations of fundamental galaxy properties, such as luminosity, morphology, and star formation rates with environment, providing new constraints on the mechanisms that drive the evolution of galaxies. This study also introduces a new maximum likelihood algorithm to recover the true distribution function of galaxies from an incomplete sample. This algorithm is ideally suited for modern-day surveys that gather a large amount of information about each object. The R-band luminosity function (GLF) shows no variation among clusters or between the field and clusters, with the exception of an enhancement of the luminous tip of the GLF in clusters. However, the GLF of quiescent galaxies steepens significantly between the field and clusters and is not universal in clusters either, suggesting that star formation properties may be more strongly correlated than the luminosity function with environment. The U-band GLF in clusters is slightly steeper than the R-band GLF, indicating that cluster galaxies are bluer at fainter magnitudes and that the GLF is thus weakly sensitive to star formation, dust, or metallicity effects. To constrain the mechanisms that shape the morphologies of cluster galaxies, we have calculated separate R-band luminosity functions for galaxy bulges and disks. Their distribution as a function of morphology and environment indicates that intermediate- and early-type galaxies can be generated from late-type galaxies by increasing the luminosity of the bulge, but not by fading the disks alone, favoring galaxy-galaxy interactions or mergers as the primary morphological transformation mechanism. Finally, we find a residual correlation of star formation with environment even after accounting for environmental variations of morphology, stellar mass, and stellar age. Thus, the star formation gradient in clusters is not just another aspect of the morphology-density relation, and cannot be solely the result of initial conditions, but must partly be due to subsequent evolution through a mechanism (or mechanisms) sensitive to environment. These results thus constitute a true "smoking gun" pointing to the effect of environment on the later evolution of galaxies
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
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Testing both Modes of Galaxy Formation: A Closer Look at Galaxy Mergers and Gas Accretion
No full textThis thesis focuses primarily on how two important processes --- galaxymergers and gas accretion from the surrounding intergalactic medium ---affect the evolution of galaxies.Using post-starburst, or E+A, galaxies as a marker sample that undergoesa rapid transition from gas-rich star-forming galaxies to quiescent,passively-evolving E/S0s, we study what triggers E+A evolution andwhat E+A galaxies will become after the fading of their young stellarpopulation. With high resolution HST WFPC2/ACS imaging, we investigatetheir small and large scale properties, including their detailedmorphologies, bulge fractions, color gradients, scaling relationships,and newly formed star-clusters. 70% of E+A galaxies show disturbancesand tidal features indicating a merger origin and all their propertiesare either consistent with those of E/S0s or, if left to evolve passively,will become like those of early-types.Using cosmological simulations, we study hydrogen and helium gravitationalcooling radiation from gas accretion by young galaxies, finding thatobserving optically thin cooling lines such as HeII 1640 and hydrogenHalpha is critical in understanding the nature of galaxies forming viagas-accretion. To obtain an unbiased sample of Lyman alpha blobs thatwill allow us to follow-up their optically thin Halpha lines in the NIR,we conduct a blind, wide-field, narrow-band imaging survey for Lymanalpha blobs. After searching over 4.82 deg^2, we discover four blobsthat we spectroscopically confirm to lie at z=2.3. The properties ofthese blobs are diverse: two blobs are X-ray-detected and have broadoptical emission lines (e.g., CIV) characteristic of AGN. The other50\% of blobs are not X-ray or optically-detected as AGN down tosimilar limits. The number density of the four blobs is extremely low,~3 x 10^-6 Mpc^-3, comparable to that of galaxy clusters at similarredshifts. The two X-ray undetected blobs are separated by only 70"(550 kpc) and have almost identical redshifts (corresponding to < 360kpc along the line-of-sight), suggesting that they are part of the samesystem. Given the rarity of the blobs and our discovery of a close pair,we speculate that blobs occupy the highest density regions and thus maybe precursors of today's rich cluster 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
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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