Chaotic motion and spiral structure in self-consistent models of rotating galaxies

Dissipationless N-body models of rotating galaxies, iso-energetic to a non-rotating model, are examined as regards the mass in regular and in chaotic motion. The values of their spin parameters $\lambda$ are near the value $\lambda=0.22$ of our Galaxy. We obtain the distinction between the sets of particles moving in regular and in chaotic orbits and we show that the spatial distribution of these two sets of particles is much different. The rotating models are characterized by larger fractions of mass in chaotic motion ($\thickapprox 65$) compared with the fraction of mass in chaotic motion in the non-rotating iso-energetic model ($\thickapprox 32$). Furthermore, the Lyapunov numbers of the chaotic orbits in the rotating models become by about one order of magnitude larger than in the non-rotating model. Chaotic orbits are concentrated preferably in values of the Jacobi integral around the value of the effective potential at the corotation radius. We find that density waves form a central rotating bar embedded in a thin and a thick disc with exponential surface density profile. A surprising new result is that long living spiral arms are exited on the disc, composed almost completely by chaotic orbits. The bar excites an $m=2$ mode of spiral waves on the surface density of the disc, emanating from the corotation radius. These spiral waves are deformed, fade, or disappear temporarily, but they grow again re-forming a well developed spiral pattern. Spiral arms are discernible up to 20 or 30 rotations of the bar (lasting for about a Hubble time).Comment: 30 pages, 17 figures (low resolution). Revised version. Accepted for publication in MNRAS. For high resolution figures please send email to [email protected]

The M_bh-sigma diagram, and the offset nature of barred active galaxies

From a sample of 50 predominantly inactive galaxies with direct supermassive black hole mass measurements, it has recently been established that barred galaxies tend to reside rightward of the M_bh-sigma relation defined by non-barred galaxies. Either black holes in barred galaxies tend to be anaemic or the central velocity dispersions in these galaxies have a tendency to be elevated by the presence of the bar. The latter option is in accord with studies connecting larger velocity dispersions in galaxies with old bars, while the former scenario is at odds with the observation that barred galaxies do not deviate from the M_bh-luminosity relation. Using a sample of 88 galaxies with active galactic nuclei, whose supermassive black hole masses have been estimated from their associated emission lines, we reveal for the first time that they also display this same general behavior in the M_bh-sigma diagram depending on the presence of a bar or not. A new symmetrical and non-symmetrical "barless" M_bh-sigma relation is derived using 82 non-barred galaxies. The barred galaxies are shown to reside on or up to ~1 dex below this relation. This may explain why narrow-line Seyfert 1 galaxies appear offset from the "barless" M_bh-sigma relation, and has far reaching implications given that over half of the disk galaxy population are barred.Comment: Short paper: 4 pages of text plus 4 figures and 1 table. Accepted by Ap

Stellar populations of bulges at low redshift

This chapter summarizes our current understanding of the stellar population properties of bulges and outlines important future research directions.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen E., Peletier R., Gadotti D., Springer Publishing. 34 pages, 12 figure

Incidence of the host galaxy on the measured optical linear polarization of blazars

We study the incidence of the underlying host galaxy light on the measured optical linear polarization of blazars. Our methodology consists of the implementation of simulated observations obtained under different atmospheric conditions, which are characterised by the Gaussian $\sigma$ of the seeing function. The simulated host plus active nucleus systems span broad ranges in luminosity, structural properties, redshift, and polarization; this allows us to test the response of the results against each of these parameters. Our simulations show that, as expected, the measured polarization is always lower than the intrinsic value, due to the contamination by non-polarized star light from the host. This effect is more significant when the host is brighter than the active nucleus, and/or a large photometric aperture is used. On the other hand, if seeing changes along the observing time under certain particular conditions, spurious microvariability could be obtained, especially when using a small photometric aperture. We thus give some recommendations in order to minimise both unwanted effects, as well as basic guidelines to estimate a lower limit of the true (nuclear) polarization. As an example, we apply the results of our simulations to real polarimetric observations, with high temporal resolution, of the blazar PKS 0521-365.Comment: 9 pages, 9 figures, 4 tables. Accepted for publication in MNRA

Antonio Gramsci’s impact on critical pedagogy

This paper provides an account of Antonio Gramsci’s impact on the area of critical pedagogy. It indicates the Gramscian influence on the thinking of major exponents of the field. It foregrounds Gramsci's ideas and then indicates how they have been taken up by a selection of critical pedagogy exponents who were chosen on the strength of their identification and engagement with Gramsci's ideas, some of them even having written entire essays on Gramsci. The essay concludes with a discussion concerning an aspect of Gramsci's concerns, the question of powerful knowledge, which, in the present author's view, provides a formidable challenge to critical pedagogues.peer-reviewe

The Milky Way Bulge: Observed properties and a comparison to external galaxies

The Milky Way bulge offers a unique opportunity to investigate in detail the role that different processes such as dynamical instabilities, hierarchical merging, and dissipational collapse may have played in the history of the Galaxy formation and evolution based on its resolved stellar population properties. Large observation programmes and surveys of the bulge are providing for the first time a look into the global view of the Milky Way bulge that can be compared with the bulges of other galaxies, and be used as a template for detailed comparison with models. The Milky Way has been shown to have a box/peanut (B/P) bulge and recent evidence seems to suggest the presence of an additional spheroidal component. In this review we summarise the global chemical abundances, kinematics and structural properties that allow us to disentangle these multiple components and provide constraints to understand their origin. The investigation of both detailed and global properties of the bulge now provide us with the opportunity to characterise the bulge as observed in models, and to place the mixed component bulge scenario in the general context of external galaxies. When writing this review, we considered the perspectives of researchers working with the Milky Way and researchers working with external galaxies. It is an attempt to approach both communities for a fruitful exchange of ideas.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen E., Peletier R., Gadotti D., Springer Publishing. 36 pages, 10 figure

Comércio ilegal de aves nativas em plataforma social virtual: subsídios para a perícia ambiental.

A retirada de animais da natureza e o tráfico de animais oferecem uma grande ameaça a biodiversidade. O livre comércio em plataformas sociais está ocupando um lugar notório na sociedade e para isso, nota-se a necessidade de profissionais com conhecimentos técnico-científicos para auxiliar no combate ao tráfico de animais e nos processos judiciais. O objetivo deste estudo foi reconhecer o comércio ilegal de aves nativas do Rio Grande do Sul em uma plataforma social, e avaliar seu uso como ferramenta para perícias ambientais. Foram monitorados, durante um mês, três grupos de comércio de aves na plataforma Facebook®. Os dados obtidos foram: espécie nativa ou exótica do Rio Grande do Sul, valor de venda, presença de anilha e espécies mais anunciadas. Contabilizou-se 338 anúncios, comercializando 36 espécies. Os valores variaram de R$25,00 a R$ 1.500,00 o espécime. Quatro espécies apresentam algum grau de ameaça de extinção. Seis espécies representaram 70% dos anúncios. Para os peritos ambientais e investigadores criminais, esta modalidade de comércio proporciona uma ferramenta válida para atuarem de forma mais acentuada e eficaz. Estes locais além de expor os criminosos, podem fornecer informações valiosas para o combate ao tráfico de animais silvestres