1,720,970 research outputs found
Metallicity dependent calibrations of flux based SFR tracers
No full textWe present new calibrations of the widely used , , and UV luminosity vs. star
formation rate (SFR) relations. Using our evolutionary synthesis code GALEV we
compute the different calibrations for 5 metallicities, from 1/50 solar up to 2.5 solar. We find significant changes in the calibrations for lower
metallicities compared to the standard calibrations using solar input physics.
The Impact of Starbursts and Post-Starbursts on the Photometric Evolution of High Redshift Galaxies
Get PDFWe present evolutionary synthesis models for galaxies of spectral types Sa
through Sd with starbursts of various strengths triggered at various redshifts
and study their photometric evolution before, during, and after their bursts in
a cosmological context. We find that bursts at high redshift, even very strong
ones, only cause a small blueing of their intrinsically blue young parent
galaxies. At lower redshift, even small bursts cause a significant blueing of
their intrinsically redder galaxies. While the burst phase is generally short,
typically a few hundred Myr in normal-mass galaxies, the postburst stage with
its red colors and, in particular the very red ones for early bursts at high
redshift, is much longer, of the order of several Gyr. Even without any dust,
which in the postburst stage is not expected to play an important role anyway,
models easily reach the colors of EROs in the redshift range z=2 through z=0.5
after starbursts at redshifts between 2 and 4. We therefore propose a third
alternative for the ERO galaxies beyond the two established ones of passive
galaxies vs. dusty starbursts: the dust-free post-(strong-)starbursts. A very
first comparison of our models to HDF data with photometric redshifts shows
that almost all of the outliers that could not be described with our chemically
consistent models for undisturbed normal galaxy types E through Sd can now be
explained very well. Galaxies in the redshift range from z=2.5 to z=0.5 that
are redder, and in some cases much redder, than our reddest undisturbed model
for a high-metallicity classical elliptical are well described by
post-starburst models after starbursts at redshifts between 2 and 4. Galaxies
bluer than our bluest low metallicity Sd model, most of which have redshifts
lower than 1, are well explained by ongoing starbursts.Comment: 12 pages, accepted by Astron. & Astrophysics Nov. 17, 200
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
Evolutionary synthesis models for the formation of S0 galaxies in clusters
No full textRich galaxy clusters in the local Universe show a large population of S0 galaxies
(~40% of all luminous galaxies). With increasing redshift the fraction of this S0
galaxy population is observed to strongly decrease (e.g. by a factor ~ to
) in favor of the spiral galaxy fraction while the number of bright ellipticals
does not seem to change. The infalling field galaxy population that successively builds
up the cluster also is spiral rich and S0 poor. It has hence been suspected that galaxy
transformation processes, either due to galaxy – galaxy or to galaxy – ICM
interactions, are responsible for this change. Complementing dynamical and morphological
studies, we use evolutionary synthesis models describing various possible effects of
those interactions on the star formation rates of the infalling spirals. We study the
effects of starbursts of various strengths as well as of the truncation of star formation
on the color and luminosity evolution of model galaxies of various spectral types.
Comparison with observed properties of the local S0 galaxy population is used to
constrain possible S0 formation mechanisms. We find that star formation truncation
in spiral galaxies earlier than Sd-type, if occurring not too long ago, as well as
starbursts more than 3 Gyr ago and followed by complete star formation extinction in
spirals – again earlier than Sd– may well account for the observed average S0
luminosities and colors. Late-type galaxies (Sd), even after a strong burst, remain
either too blue or too faint. Our results are in agreement with studies of spectral
features of cluster S0s but allow for stronger constraints
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
Chemically Consistent Evolutionary Synthesis
Get PDFTo account for the range of stellar metallicities in local galaxies and for the increasing importance of low metallicities at higher redshift we present chemically consistent models for the spectral and chemical evolution of galaxies over cosmological timescales. We discuss advantages, limitations and future prospects of our approach
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
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