Faint dwarf galaxies in nearby clusters

Besides giant elliptical galaxies, a number of low-mass stellar systems inhabit the cores of galaxy clusters, such as dwarf elliptical galaxies (dEs/dSphs), ultra-compact dwarf galaxies (UCDs), and globular clusters. The detailed morphological examination of faint dwarf galaxies has, until recently, been limited to the Local Group (LG) and the two very nearby galaxy clusters Virgo and Fornax. Here, we compare the structural parameters of a large number of dEs/dSphs in the more distant clusters Hydra I and Centaurus to other dynamically hot stellar systems.Comment: 2 pages, 1 figure; to appear in "A Universe of Dwarf Galaxies: Observations, Theories, Simulations", held in Lyon, France (June 14-18, 2010), eds. M. Koleva, P. Prugniel & I. Vauglin, EAS Series (Paris: EDP

L’éducation mondiale dans une perspective locale

Le présent article a pour but d'examiner l'éducation mondiale en fonction des conditions dans lesquelles elle peut devenir acceptable par les enseignantes et par les enseignants ainsi que par les citoyennes et les citoyens. Ces conditions, qui commandent l'exercice de notre activité quotidienne, sont locales et particulières. Ainsi peut-on mettre de l'avant les principes fondamentaux de la citoyenneté mondiale, intellectuellement éclairants et accessibles dans notre vécu. L'étude distingue l'éducation dans une perspective planétaire, laquelle englobe des préoccupations tant écologiques que socioculturelles, de l'éducation aux droits humains, objet central des observations de l'auteur.This article examines global education in terms of the conditions needed for these programmes to gain acceptance by both teachers and citizens in general. The conditions noted are local and specific and direct our everyday activities. This allows the author to propose the underlying principles of global citizenship; these principles would be intellectually illumi- nating and accessible to our experience. The study compares global education, which includes both ecological and socio-cultural concerns with human rights education, which is the authors main focus.Este artfculo examina la educacion mundial en funcion de las condiciones que le permitan ser aceptada tanto por los maestros como por los ciudadanos en general. Estas condi- ciones, que dirigen el ejercicio de nuestra actividad cotidiana, son locales y particulates. Asi, nos preguntamos si puede darsele prioridad a los principios fondamentales de la ciudadanïa mundial, intelectualmente esclarecedores y accesibles en nuestra vida comûn. El artfculo distingue la educacion con una perspectiva planetaria, que incluye preocupaciones tanto ecologicas como socioculturales, de la educacion sobre los derechos humanos, objeto central de las observaciones del autor.Der vorliegende Artikel untersucht, unter welchen Umstânden die weltaufgeschlossene Erziehung fur die Lehrer/Lehrerinnen und fur die Burger/Burgerinnen akzeptabel werden kann. Dièse Umstânde, die unsere tâgliche Tâtigkeit bestimmen, sind lokal und speziell. Daraus geht hervor, dass die intellektuell aufklàrenden und praktisch zugânglichen Grundprinzipien des Weltbûrgerstatus formuliert werden kônnen. Es wird zwischen weltaufgeschlossener Erziehung- die die ôkologischen und soziokulturellen Problème mit einschliefit - und Menschenrechtslehre unterschieden, wobei Letztere im Mittelpunkt dieser Untersuchung steht

A census of ultra-compact dwarf galaxies in nearby galaxy clusters

Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also been confirmed in the twice as distant Hydra I and Centaurus clusters. Having (nearly) complete samples of UCDs in some of these clusters allows the study of the bulk properties with respect to the environment they are living in. Moreover, the relation of UCDs to other stellar systems in galaxy clusters, like globular clusters and dwarf ellipticals, can be investigated in detail with the present data sets. The general finding is that UCDs seem to be a heterogenous class of objects. Their spatial distribution within the clusters is in between those of globular clusters and dwarf ellipticals. In the colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and might have originated from the amalgamation of massive star cluster complexes in merger or starburst galaxies.Comment: 6 pages, 3 figures; to appear in "A Universe of Dwarf Galaxies: Observations, Theories, Simulations", held in Lyon, France (June 14-18, 2010), eds. M. Koleva, P. Prugniel & I. Vauglin, EAS Series (Paris: EDP

Susanne Soederberg, Global Governance in Question: Empire, Class and the New Common Sense in Managing North South Relations. Winnipeg and London: Arbeiter Ring Publishing and Pluto Press, 2006, 206 pp., $24.95 paper.

Academics and activists who have followed the discussions of globalization in the World Social Forum literature and in progressive publications will readily agree with Soederberg that globalization does not simply signify an “inevitable and unstoppable” (26) process. In focusing on the concept of global governance, she contributes to the critical problematization of an international economic regime which all too frequently is treated as benevolent in its consequences and independent of politics. Soederberg strongly resists mythological descriptions of global (and regional) financial and other economic regimes, by pursuing an historical - materialist analysis of the emergence of the relevant organizations and institutions, always identifying the role of power, political influence and political planning in their construction. She nimbly walks the reader through a plethora of institutions which even the informed lay-person and political activist will not know how to distinguish. She obviously possesses enormous knowledge of their workings and their history. In this sense this is a very useful book to read, particularly for those who are not specialists in the fields of international relations, Third World development or the politics of international financial institutions

Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments

We present the results of the first search for Ultra Compact Dwarfs (UCDs) in the Perseus Cluster core, including the region of the cluster around the unusual Brightest Cluster Galaxy (BCG) NGC 1275. Utilising Hubble Space Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD candidates with half-light radii 10 pc < r_e < 57 pc out to a distance of 250 kpc from the cluster centre, covering a total survey area of ~70 armin^2. All UCDs in Perseus lie in the same size-luminosity locus seen for confirmed UCDs in other regions of the local Universe. The majority of UCDs are brighter than M_R = -10.5, and lie on an extrapolation of the red sequence followed by the Perseus Cluster dwarf elliptical population to fainter magnitudes. However, three UCD candidates in the vicinity of NGC 1275 are very blue, with colours (B-R)_0 < 0.6 implying a cessation of star formation within the past 100 Myr. Furthermore, large blue star clusters embedded in the star forming filaments are highly indicative that both proto-globular clusters (GCs) and proto-UCDs are actively forming at the present day in Perseus. We therefore suggest star forming filaments as a formation site for some UCDs, with searches necessary in other low redshift analogues of NGC 1275 necessary to test this hypothesis. We also suggest that tidal disruption of dwarf galaxies is another formation channel for UCD formation in the core of Perseus as tidal disruption is ongoing in this region as evidenced by shells around NGC 1275. Finally, UCDs may simply be massive GCs based on strong similarities in the colour trends of the two populations.Comment: 18 pages, 20 figures, 3 tables. Accepted for publication in MNRA

The specific frequencies of ultra-compact dwarf galaxies

We aim at quantifying the specific frequency of UCDs in a range of environments and at relating this to the frequency of globular clusters (GCs) and potential progenitor dwarf galaxies. Are the frequencies of UCDs consistent with being the bright tail of the GC luminosity function (GCLF)? We propose a definition for the specific frequency of UCDs, S_{N,UCD}=N_{UCD}*10^{0.4*(M_{V,host}-M_{V,0})}*c_{w}. The parameter M_{V,0} is the zeropoint of the definition, chosen such that the specific frequency of UCDs is the same as those of globular clusters, S_{N,GC}, if UCDs follow a simple extrapolation of the GCLF. The parameter c_{w} is a correction term for the GCLF width sigma. We apply our definition of S_{N,UCD} to results of spectroscopic UCD searches in the Fornax, Hydra and Centaurus galaxy clusters, two Hickson Compact Groups, and the Local Group. This includes a large database of 180 confirmed UCDs in Fornax. We find that the specific frequencies derived for UCDs match those of GCs very well, to within 10-50%. The ratio {S_{N,UCD}}/{S_{N,GC}} is 1.00 +- 0.44 for the four environments Fornax, Hydra, Centaurus, and Local Group, which have S_{N,GC} values. This good match also holds for individual giant galaxies in Fornax and in the Fornax intracluster-space. The error ranges of the derived UCD specific frequencies in the various environments then imply that not more than 50% of UCDs were formed from dwarf galaxies. We show that such a scenario would require >90% of primordial dwarfs in galaxy cluster centers (<100 kpc) to have been stripped of their stars. We conclude that the number counts of UCDs are fully consistent with them being the bright tail of the GC population. From a statistical point of view there is no need to invoke an additional formation channel.Comment: 11 pages, 6 figures, A&A accepted. Press release http://www.aanda.org/index.php?option=com_content&task=view&id=788&Itemid=27

The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological? Dynamics of NGC 3311 and its globular cluster system

NGC 3311 is the central cD galaxy of the Hydra I cluster. We use globular clusters around NGC 3311, combined with kinematical data of the galaxy itself, to investigate the dark matter distribution in the central region of Hydra I. Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask spectroscopy, are used to calculate velocity dispersions which are well defined out to 100 kpc. NGC 3311 is the most distant galaxy for which this kind of study has been performed. We also determine velocity dispersions of the stellar component from long slit spectroscopy out to 20 kpc. Moreover, we present a new photometric model for NGC 3311 in the V-band. We search for a dark halo which in the context of a spherical Jeans model. We also compare the radial velocity distributions of globular clusters and planetary nebulae. The projected stellar velocity dispersion rises from 185 km/s to 350 km/s at a radius of 20 kpc. The globular cluster dispersion rises as well from 500 km/s at 10 kpc to about 800 km/s at 100 kpc, comparable to the velocity dispersion of the cluster galaxies. A dark matter halo with a core reproduces well the velocity dispersions of stars and globular clusters simultaneously under isotropy. The central stellar velocity dispersions predicted by cosmological NFW halos are less good representations, while the globular clusters allow a wide range of halo parameters. A suspected radial anisotropy of the stellar population aggravates the deviations. However, we find discrepancies with previous kinematical data, which we cannot resolve and may indicate a more complicated velocity pattern. Although one cannot conclusively demonstrate that the dark matter halo of NGC 3311 has a core rather than a cusp, a core seems to be preferred by the present data. A more complete velocity field and an analysis of the anisotropy is required to reach firm conclusions.Comment: 8 pages, 5 figures, abstract abridged, accepted for publication in A&

The Fundamental Plane of Early-Type Galaxies as a Confounding Correlation

Early-type galaxies are characterized by many scaling relations. One of them, the so-called fundamental plane is a relatively tight correlation between three variables, and has resisted a clear physical understanding despite many years of intensive research. Here, we show that the correlation between the three variables of the fundamental plane can be the artifact of the effect of another parameter influencing all, so that the fundamental plane may be understood as a confounding correlation. Indeed, the complexity of the physics of galaxies and of their evolution suggests that the main confounding parameter must be related to the level of diversification reached by the galaxies. Consequently, many scaling relations for galaxies are probably evolutionary correlations