1,721,059 research outputs found
Stellar Archeology: A Cosmological View of dSphs
No full textThe origin of dwarf spheroidal galaxies (dSphs) is investigated in a global cosmological context by simultaneously following the evolution of the Galaxy and its dwarf satellites. This approach enables to study the formation of dSphs in their proper birth environment and to reconstruct their own merging histories. The proposed picture simultaneously accounts for several dSph and Milky Way properties, including the Metallicity Distribution Functions of metal-poor stars. The observed features are interpreted in terms of physical processes acting at high redshifts
Spectrophotometric investigations of the blue compact dwarf galaxy Mrk 35
No full textPreliminary results from a detailed spectrophotometric analysis of the blue compact dwarf galaxy (BCD) Mrk 35 are presented. We have performed deep UBVRI broad-band and H-alpha narrow-band optical observations, near-infrared (JHK(s)) imaging and long-slit spectroscopy of the galaxy. Mrk 35 is composed of a very young starburst population distributed in a bar-like structure, placed on top of an underlying, older stellar host galaxy. Using predictions of evolutionary synthesis models, we estimate the ages of both the starburst regions and the underlying stellar component
Optical multi-band analyses of blue compact dwarf galaxies
No full textWe are currently analysing image data for a large sample of blue compact dwarf galaxies (BCDs), obtained in multiple optical broad- and narrow-band filters. We present preliminary results of a multi-band analysis of two typical BCDs, Mrk 5 and I Zw 123, for which surface-brightness profiles, colour profiles, colour maps and H-alpha equivalent-width maps have been derived. We demonstrate how a combination of these different processing methods allows a separate analysis of the young and old stellar populations with respect to their colours and spatial distributions. By comparing the derived colours with the predictions of evolutionary synthesis models, we estimate ages of the distinct stellar populations. The surface-brightness profiles of Mrk 5 show an exponential decay at large photometric radii, with slopes typically found for BCDs. In the case of the very compact object I Zw 123, the surface-brightness profile of the underlying stellar component can be described either by an exponential or an R-1/4 law. We discuss briefly how noise effects can influence the intrinsic slope of surface brightness profiles at low surface-brightness levels. For compact objects with extended starbursts, the study of the underlying stellar population can thereby be rendered difficult
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
An investigation of the luminosity-metallicity relation for a large sample of low-metallicity emission-line galaxies
No full textContext. We present 8.2 m VLT spectroscopic observations of 28 H i
An imaging and spectroscopic study of the very metal-deficient blue compact dwarf galaxy Tol 1214-277
No full textWe present a spectrophotometric study based on VLT/FORS I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z similar to Z(.)/25). The data show that roughly half of the total luminosity of the BCD originates from a bright and compact starburst region located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and similar to 170 late-type nitrogen Wolf-Rayet stars located within a compact region with less than or similar to 500 pc in diameter. For the first time in a BCD, a relatively strong [Fe V] lambda 4227 emission line is seen which together with intense He II lambda 4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation originates from both Wolf-Rayet stars and radiative shocks in the starburst region. The structural properties of the low surface brightness (LSB) component underlying the starburst have been investigated by means of surface photometry down to 28 B mag arcsec(-2). We find that, for a surface brightness level fainter than similar to 24.5 B mag arcsec(-2), an exponential fitting law provides an adequate approximation to its radial intensity distribution. The broadband colors in the outskirts of the LSB component of Tol 1214-277 are nearly constant and are consistent with an age below one Gyr. This conclusion is supported by the comparison of the observed spectral energy distribution (SED) of the LSB host with theoretical SEDs
Chandra observations of the three most metal deficient blue compact dwarf galaxies known in the local universe, SBS 0335-052, SBS0335-052W, and I Zw 18
No full textWe present an X-ray study of the three most metal deficient blue compact dwarf (BCD) galaxies known in the local universe, based on deep Chandra observations of SBS 0335-052 (0.025 Z(circle dot)), SBS 0335-052W (0.02 Z(circle dot)), and I Zw 18 (0.02 Z(circle dot)). All three are detected, with more than 90% of their X-ray emission arising from pointlike sources. The 0.5-10.0 keV luminosities of these point sources are in the range (1.3-8.5); 10(39) ergs s(-1). We interpret them to be single or a collection of high-mass X-ray binaries, the luminosities of which may have been enhanced by the low metallicity of the gas. There are hints of faint extended diffuse X-ray emission in both SBS 0335-052 and I Zw 18, probably associated with the superbubbles visible in both BCDs. The spectrum of I Zw 18 shows an O VIII hydrogen-like emission line. The best spectral fit gives an O overabundance of the gas in the X-ray point source by a factor of similar to7 with respect to the Sun, or a factor of similar to350 with respect to the O abundance determined for the H II region
Hi-rich dwarf galaxies in the Hydra I cluster II. Spectroscopic data
No full textWe present spectrophotometric data for a sample of 15 H I-selected dwarf galaxies in the Hydra I cluster (see Duc et ai. 1999, Paper I). Long-slit spectra were obtained along an axis including the nucleus and the brightest H II region in each galaxy. The oxygen abundance was estimated from the emission lines using various methods. AII dwarfs host one or several star-forming regions that are, for the most Dart, located outside the nucleus. We did not find in this survey any extremely metal-deficient objects, but we did observe some galaxies with a surprisingly high metallicity for their luminosity. In a following paper in this series, we will discuss the global properties of the H I-rich dwarfs in the Hydra I cluster and focus on their dependence on the environment
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
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