1,721,003 research outputs found
Galaxy activity and interaction: the optical view
No full textThe relevance of interaction to the presence of Seyfert or starburst activity in the nuclei of galaxies is examined. We focus the attention on the close environments of spectroscopically selected samples of Seyfert-1, Seyfert-2 and starburst galaxies. In particular the results of a statistical procedure aimed at finding physical pairs are tested with redshift measurements of the identified pairs. Seyfert and starburst galaxies show an excess of physical companions compared to normal galaxies. This excess tends to increase as one moves from Seyfert to starburst galaxies
Interpreting the galaxy group CG J1720-67.8 through evolutionary synthesis models
Full text linkThis paper is part of a series devoted to a detailed analysis of the properties of
the compact group CG J1720-67.8 and its member galaxies with the aim of shedding light
on its evolutionary history.
Here we interpret our previously published observational results through comparison
with chemically
consistent spectrophotometric evolutionary synthesis models to gain further
clues to the evolution of the galaxies in this group.
In order to reduce the number of free parameters, we considered the simplest case
of a single burst of star-formation turned on after 11-12 Gyr of undisturbed
galaxy evolution. However, we also briefly explored the effect of multiple,
interaction-induced bursts of star-formation.
We found that the two spiral galaxies are consistent with interaction-induced strong
starbursts switched on ~40 to 180 Myr ago and still active. For the early-type galaxy, a
\la0.9-1.3 Gyr old star-formation event (depending on the considered model)
appears consistent with the observed properties.
The comparison with models cannot rule out the possibility that this galaxy is
already the result of a merger. Alternatively, a star-formation episode in this
galaxy might have been triggered by gas inflow as a consequence of the interaction
with the companion galaxies. Estimates of galaxy masses were derived from the comparison
with the models. Finally our results are discussed in comparison with other
well-studied, poor galaxy systems
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
The Seyfert II galaxy Tol1238-364 and its companion ESO381-G009: long slit spectroscopy and IRAS data analysis
No full textThe results of a spectroscopic study of the pair of galaxies Tol 1238-364 and ESO 381-G009 are presented. Long-slit spectroscopy at different slit position angles combined with Laplace filtering of Hα images of the two galaxies allowed to isolate several circumnuclear and extranuclear regions. Physical properties have been derived by means of a grid of photoionization models computed with the code Cloudy 90. Star formation rates in both galaxies have been calculated and compared with their infrared emission, obtained from IRAS data after application of the Maximum Entropy method
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
Analysis of the interaction effects in the southern galaxy pair Tol 1238-364 and ESO 381-G009
No full textIn the context of the connection among galaxy-galaxy interaction, starbursts, and nuclear activity, we present and discuss a quantitative morphological analysis based on BVR images and a detailed spectroscopic investigation of two interacting galaxies, the Seyfert 2 Tol 1238-364 (IC 3639) and its companion ESO 381-G009, forming a triple system with ESO 381-G006. Broadband optical photometry is complemented by Hα imaging, which provides information about the distribution of star-forming regions across the galaxies. Long-slit spectroscopic data obtained at different position angles of the slit are employed to determine the physical conditions of circumnuclear and extranuclear regions. A mixture of thermal and nonthermal ionizing radiation is found in the surroundings of the nucleus of Tol 1238-364, and the energy budget supports the presence of a circumnuclear starburst. Several regions in both the galaxies show anomalous line ratios: additional ionization by shock heating and low ionization of some extranuclear H II regions are suggested as possible explanations. An analysis of the emission-line profiles reveals the presence of a broad Hα component in the nuclear region of Tol 1238-364. Independent estimates of the star formation rates (SFRs) were obtained through flux-calibrated Hα images and far-infrared (FIR) emission in the four IRAS bands. Overall, SFR densities have been compared with the SFR densities derived from Hα emission in the individual regions of the galaxies sampled by long-slit spectra. In both the galaxies an enhancement of the star formation activity with respect to isolated galaxies is revealed. The prevalence of starburst or nuclear activity has been examined through FIR color indices. The interaction scenario is discussed on the basis of the observed galaxy properties
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
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