1,723,710 research outputs found
Disformal invariance of second order scalar-tensor theories: Framing the Horndeski action
No full textThe Horndeski action is the most general one involving a metric and a scalar field that leads to second-order field equations in four dimensions. Being the natural extension of the well-known scalar-tensor theories, its structure and properties are worth analyzing along the experience accumulated in the latter context. Here, we argue that disformal transformations play, for the Horndeski theory, a similar role to that of conformal transformations for scalar-tensor theories a là Brans–Dicke. We identify the most general transformation preserving second-order field equations and discuss the issue of viable frames for this kind of theory, in particular, the possibility to cast the action in the so-called Einstein frame. Interestingly, we find that only for a subset of the Horndeski Lagrangian such a frame exists. Finally, we investigate the transformation properties of such frames under field redefinitions and frame transformations and their reciprocal relationship
An extended ultraviolet ring around the SB0 galaxy NGC 4262
No full textWe present Galaxy Ultraviolet Explorer (GALEX) satellite observations of the SB0 galaxy NGC 4262 where we detect an extended, outer ring studded with UV-bright knots surrounding the galaxy body. Such a structure, not visible at optical wavelengths, is coupled with a ring of atomic (HI) gas. We will show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We also model the kinematics of the ring(s) and of the galaxy body. Their kinematics is not coupled with that of the galaxy stars. We suggest that NGC 4262 has undergone a major gas stripping event in the past that was the origin of the present "necklace" of UV-bright knots
A Massive Counter-Rotating Gas Disk in a Spiral Galaxy,
No full textIN some galaxies that have little gas remaining from the epoch of galaxy formation, the gas that is present rotates in the opposite sense to the stars1-4. It is thought that this counter-rotating gas may result from the capture by a massive early-type galaxy of a gas-rich dwarf galaxy that was orbiting in the opposite sense to the main galaxy’s rotation; but as there are few examples of galaxies with counter-rotating gas, we have little information about the details of this process. Here we present optical spectra of the spiral5,6 galaxy NGC3626, which clearly show the presence of counter-rotating ionized gas; combining these results with preexisting atomic hydrogen data7 leads to an estimate of 109 Msolar for the mass of the gas. Spiral galaxies generally contain substantial amounts of gas left over from the formation epoch, which would be co-rotating with the stars; this gas should interact strongly with the counter-rotating gas on a relatively short timescale, causing it to fall towards the centre of the galaxy. We therefore propose that the counter-rotating gas in NGC3626 has been captured recently; the merger process is just beginning
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
Study of ISM tracers in galaxies
No full textWe collected data for two samples of normal and interacting galaxies for a total of 2953 galaxies having fluxes in one or more of the following wavebands: FIR, 21 cm line, CO(1-0) lines and soft X-ray. The large set of data obtained allowed us to revisit some of the already known relations between the different tracers of the interstellar medium (ISM), such as the link between the FIR flux and the CO line emission, the relation between X-ray emission and the blue or FIR luminosity. The relation lacking from observations for early-type galaxies has been discussed and explained in detail in the frame of a suitable theoretical model, obtained by coupling chemo-dynamical N-body simulations with a dusty spectrophotometric code of population synthesis
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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