Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical composition analysis and metallicity-luminosity relations

(Abridged) We performed a multiwavelength analysis of a sample of starburst galaxies that show the presence of a substantial population of very young massive (WR) stars. Here we present the global analysis of the derived photometric and chemical properties. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties with previous observations and galaxy evolution models. Attending to their absolute B-magnitude many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both C(Hb) and Wabs increase with increasing metallicity. We detected a high N/O ratio in objects showing strong WR features. The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained using empirical calibrations, finding that (i) the Pilyugin method is the best suitable empirical calibration, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are related to the optical/NIR luminosity; the dispersion is consequence of the differences in the star-formation histories. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Our detailed analysis is fundamental to understand the nature of galaxies showing strong starbursts, as well as to know their star formation history and the relationships with the environment.Comment: 30 pages, 22 figures, accepted to A&A. Updated with the final version

The tidally disturbed luminous compact blue galaxy Mkn 1087 and its surroundings

We present new broad-band optical and near-infrared CCD imaging together with deep optical intermediate-resolution spectroscopy of Mkn 1087 and its surrounding objects. We analyze the morphology and colors of the stellar populations of the brightest objects, some of them star-formation areas, as well as the kinematics, physical conditions and chemical composition of the ionized gas associated with them. Mkn 1087 does not host an Active Galactic Nucleus, but it could be a Luminous Compact Blue Galaxy. Although it was classified as a suspected Wolf-Rayet galaxy, we do not detect the spectral features of these sort of massive stars. Mkn 1087 shows morphological and kinematical features that can be explained assuming that it is in interaction with two nearby galaxies: the bright KPG 103a and a dwarf ($M_B\sim-18$) star-forming companion. We argue that this dwarf companion is not a tidal object but an external galaxy because of its low metallicity [12+log(O/H) = 8.24] with respect to the one derived for Mkn 1087 [12+log(O/H) = 8.57] and its kinematics. Some of the non-stellar objects surrounding Mkn 1087 are connected by bridges of matter with the main body, host star-formation events and show similar abundances despite their different angular distances. These facts, together their kinematics, suggest that they are tidal dwarf galaxies formed from material stripped from Mkn 1087. A bright star-forming region at the south of Mkn 1087 (knot #7) does not show indications of being a tidal galaxy or the product of a merging process as suggested in previous works. We argue that Mkn 1087 and its surroundings should be considered a group of galaxies.Comment: Accepted by A&A, 21 pages, 13 figures, 8 table

Stochastic vortex dynamics in two-dimensional easy-plane ferromagnets: Multiplicative versus additive noise

We study how thermal fluctuations affect the dynamics of vortices in the two-dimensional classical, ferromagnetic, anisotropic Heisenberg model depending on their additive or multiplicative character. Using a collective coordinate theory, we analytically show that multiplicative noise, arising from fluctuations in the local field term of the Landau-Lifshitz equations, and Langevin-like additive noise both have the same effect on vortex dynamics (within a very plausible assumption consistent with the collective coordinate approach). This is a non-trivial result, as multiplicative and additive noises usually modify the dynamics quite differently. We also carry out numerical simulations of both versions of the model finding that they indeed give rise to very similar vortex dynamics.Comment: 10 pages, 6 figure

Dynamics of crystalline tensionless surfaces

4 pages, 4 figures.-- PACS nrs.: 68.35.Rh, 81.10.Aj, 81.10.Bk, 81.15.Hi.We introduce a model for two-dimensional crystalline tensionless surfaces. In equilibrium, the model exhibits a roughening transition to the high temperature phase of the sine-Gordon (sG) model, though its initial stages are rougher and described by the linear molecular beam epitaxy equation; the transition temperature is about half the sG one. Depending on distance to equilibrium and temperature, the model can behave as a nonmoving flat interface, a moving interface with oscillatory roughness, or a rough moving interface. Possible experimental applications are discussed.This work has been supported by CICyT (Spain) Grant No. MAT95-0325.Publicad

Bodegas subterráneas en Zamora

En número dedicado a: La provincia de Zamor

Crystalline lattice effects on tensionless surface dynamics

9 pages, 5 figures.A new model is introduced for two-dimensional crystalline interfaces with negligible surface tension. The model is given by a discrete version of the linear molecular beam epitaxy (MBE) equation plus an additional term periodic in the interface height variable. Langevin dynamics simulations and analytical arguments show that the model exhibits a roughening transition to the high temperature phase of the sine-Gordon model, whose initial stages are nevertheless described by the scaling of the linear MBE equation. Out of equilibrium, the model can have three different behaviors depending on temperature and deviation from equilibrium: A non-moving flat interface, a moving interface with oscillatory roughness, and a moving interface which shows scaling. Possible connections to experiments are discussed.This work has been supported by CICyT (Spain) grant MAT95-0325.Publicad

Analyzing gender inequality through large-scale Facebook advertising data

Online social media are information resources that can have a transformative power in society. While the Web was envisioned as an equalizing force that allows everyone to access information, the digital divide prevents large amounts of people from being present online. Online social media in particular are prone to gender inequality, an important issue given the link between social media use and employment. Understanding gender inequality in social media is a challenging task due to the necessity of data sources that can provide large-scale measurements across multiple countries. Here we show how the Facebook Gender Divide (FGD), a metric based on aggregated statistics of more than 1.4 Billion users in 217 countries, explains various aspects of worldwide gender inequality. Our analysis shows that the FGD encodes gender equality indices in education, health, and economic opportunity. We find gender differences in network externalities that suggest that using social media has an added value for women. Furthermore, we find that low values of the FGD are associated with increases in economic gender equality. Our results suggest that online social networks, while suffering evident gender imbalance, may lower the barriers that women have to access informational resources and help to narrow the economic gender gap

Digital Competences for Improving Digital Inclusion in E-Government Services: A Mixed-Methods Systematic Review Protocol

The e-government requires citizens that have a certain level of digital skills. Contact restrictions caused by the COVID-19 pandemic has accelerated the digital transformation of Public Administration in most countries and has increased the social digital divide. Therefore, the training of citizens in digital competences is one of the main challenges of the knowledge society. This mixed-methods systematic review protocol aims to synthesize quantitative and qualitative findings about conditioning factors of digital inclusion, in a multidimensional perspective, related with the education, healthcare and welfare sectors and the political actions involved to improve the digital competences of citizenship for allowing and enhancing their interactions with these online public services. The protocol has been written following the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) guidelines. Nine databases including Web of Science, Scopus, Educational Resources Information Center Library and Information Science Abstracts (LISA), ProQuest, MEDLINE, PubMed, SocINDEX and Cairn.info will be searched for peer-reviewed empirical studies published from 2011 or later. Grey literature and citation chaining will be undertaken. Quantitative, qualitative and mixed-methods studies will be included. Data items will be extracted and coded in a standardized format. A convergent segregated approach to synthesis and integration will be used. The results will be of interest to educational policymakers who want to take into account citizens'' digital skills in the design of online services and lifelong learning programs