1,721,019 research outputs found
Star formation history of early-type galaxies in low density environments IV. What do we learn from nuclear line-strength indices?
No full textIn this paper we analyze the line-strength indices in the Lick-system measured by Longhetti et al. (1998a, b) for a sample of 51 early-type galaxies located in low density environments (LDE) and showing signatures of fine structures and/or interactions. The sample contains 21 shell-galaxies and 30 members of interacting pairs. Firstly we perform a preliminary comparison between three different sources of calibrations of the line strength indices, namely Buzzoni et al. (1992, 1994), Worthey (1992), Worthey et al. (1994) and Idiart et al. (1995), derived from stars with different effective temperature, gravity, and metallicity. Looking at the three indices in common, i.e. Mg2, Fe5270, and HP, the calibrations by Buzzoni et al. (1992, 1994), Worthey (1992) and Worthey et al. (1994) lead to mutually consistent results. The calibration of H beta by Idiart et al. (1995) can be compared with the previous ones only for a limited range of ages, in which good agreement is found. Mg2 and Mgb indices predicted by the Idiart's et al. (1995) fitting functions result to be systematically lower than those obtained from using Worthey (1992) calibrations. Secondly, we discuss the properties of the galaxies in our sample by comparing them both with theoretical Single Stellar Populations (SSPs) and the normal galaxies of the Gonzalez (1993: G93) sample. The analysis is performed by means of several diagnostic planes. In the sigma, Mg2, Fe5270 and Fe5335 space, normal, shell- and pair-galaxies have a different behavior. First of all, normal and pair-galaxies follow the universal a vs. Mg2 relation, whereas shell-galaxies lie above it; secondly the Fe versus Mg2 relation of normal, shell- and pair-galaxies is flatter than the theoretical expectation. This fact hints for enhancement of alpha-elements with respect to solar partition in galaxies with strong Fe indices and/or high velocity dispersion, mass and luminosity in turn. In the sigma vs. H beta plane normal galaxies seem to follow a nice relation suggesting that objects with shallow gravitational potential have strong H beta values (youth signature?), whereas shell-and pair-galaxies scatter all over the plane. A group of galaxies with deep gravitational potential and strong HP is found. Is this a signature of recent star formation? In the H beta vs. [MgFe] plane,(1) which is perhaps best suited to infer the age of the stellar populations, the peculiar galaxies in our sample show nearly the same distribution of the normal galaxies in the G93 sample. There is however a number of peculiar galaxies with much stronger H beta. Does this mean that the scatter in the H beta vs. [MgFe] plane, of normal, shell- and pair galaxies has a common origin, perhaps a secondary episode of star formation? We suggest that, owing to their apparent youth, shell- and pair-galaxies should have experienced at least one interaction event after their formation. The explanation comes natural for shell- and pair-galaxies where the signatures of interactions are evident. It is more intrigued in normal galaxies (perhaps other causes may concur). Noteworthy, the distribution in the H beta vs. [MgFe] plane of normal, shell- and pair-galaxies is confined within a narrow strip that runs significantly steeper than the path followed by aging SSPs. This feature is explained as due to metal enrichment always accompanying star formation. Shell-galaxies encompass the whole range of ages inferred from the HP vs, [MgFe] plane, indicating that among them recent and old interaction/acquisition events are equally probable. If shells are formed at the same time at which the rejuvenating event took place, shells ought to be long lasting phenomena
Star formation history of early-type galaxies in low density environments V. Blue line-strength indices for the nuclear region
No full textWe analyze the star formation properties of a sample of 21 shell galaxies and 30 early-type galaxies members of interacting pairs, located in low density environments (Longhetti et al. 1998a, 1998b). The study is based on new models developed to interpret the information coming from 'blue' H delta/FeI, H+K(CaII) and Delta 4000 line-strength indices proposed by Rose (1984; 1985) and Hamilton (1985). We find that the last star forming event that occurred in the nuclear region of shell galaxies is statistically old (from 0.1 up to several Gyr) with respect to the corresponding one in the sub-sample of pair galaxies (< 0.1 Gyr or even ongoing star formation). If the stellar activity is somehow related to the formation of shells, as predicted by several dynamical models of galaxy interaction, shells have to be considered long lasting structures. Since pair members show evidence of very recent star formation, we suggest that either large reservoirs of gas have to be present to maintain active star formation, if these galaxies are on periodic orbits, or most of the pair members in the present sample are experiencing unbound encounters
Star formation history of early-type galaxies in low density environments. III. The isophote shape parameter and nuclear line-strength indices
No full textComparative analysis of the properties of bright early-type galaxies in nearby clusters and in the field
No full textStar formation history of early-type galaxies in low density environment II. Kinematics
No full textThe present paper is a companion of two others dedicated one to the measurement of the line-strength indices (Longhetti et al. 1997a) and the second to trace back the star formation history of a sample of early-type galaxies by comparing observed indices to the predictions of new spectro-photometric models (Longhetti et al. 1997b). The sample of 51 early-type galaxies in low density environments is composed of two sub-sets of galaxies: 21 shell galaxies from the Malin & Carter (1983) catalogue tone of which shows double nucleous and has been considered as two separate objects) and 30 members of isolated interacting pairs from the Reduzzi & Rampazzo (1995) catalogue. Most of the objects show fine structures. The paper collects nuclear kinematic data together with the velocity and velocity dispersion curves of the stellar and gaseous components as a function of the distance from the galaxies centres. The galaxies heliocentric systemic velocity compares within -1 +/- 32 km s(-1) with RC3 data, while their central velocity dispersion compares within 9+/-9 km s(-1), 10+/-27 km s(-1) and 2+/-33 km s(-1) with Gonzalez (1993), Davies et al. (1987) and Carter et al. (1988) respectively. The detailed comparison between our velocity and velocity dispersion curves and those from several authors is discussed. 9 out of 22 shell galaxies nuclei show emission lines, 4 of which, using data in the literature, have line ratios char acteristic of LINERs. 10 members of pairs out of 30 show emission lines. RR 331a has a Seyfert like nucleus, while for the remaining galaxies the ([O III] lambda 5007)/H beta ratio is characteristic of low ionization regions. In a small fraction of the objects the emission component is detectable outside the central value. None of the objects in the sample shows counter-rotation of the gaseous versus the stellar component. The two components appear associated, although, in two cases there is evidence that gas and stars lie on different planes. This latter phenomenon could be associated to accretion events. Emission lines in the central part of the RR 331a show a secondary component in the emission lines profile. E 2400100 has two nuclei embedded in the main body of the galaxy. The U-shape profile of the stellar velocity profile shows the ongoing interaction of the two nuclei. V/sigma profile of shell galaxies is, finally, discussed in relation to the hypothesis of the accretion/merging origin of these 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
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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