Context. The study of intracluster light (ICL) can help us to understand the mechanisms taking place in galaxy clusters, and to place constraints on the cluster formation history and physical properties. However, owing to the intrinsic faintness of ICL emission, most searches and detailed studies of ICL have been limited to redshifts z < 0.4. Aims. To help us extend our knowledge of ICL properties to higher redshifts and study the evolution of ICL with redshift, we search for ICL in a subsample of ten clusters detected by the ESO Distant Cluster Survey (EDisCS), at redshifts 0.4 < z < 0.8, that are also part of our DAFT/FADA Survey. Methods. We analyze the ICL by applying the OV WAV package, a wavelet-based technique, to deep HST ACS images in the F814W filter and to V-band VLT/FORS2 images of three clusters. Detection levels are assessed as a function of the diffuse light source surface brightness using simulations. Results. In the F814W filter images, we detect diffuse light sources in all the clusters, with typical sizes of a few tens of kpc (assuming that they are at the cluster redshifts). The ICL detected by stacking the ten F814W images shows an 8σ detection in the source center extending over a ∼50 × 50 kpc 2 area, with a total absolute magnitude of −21.6 in the F814W filter, equivalent to about two L * galaxies per cluster. We find a weak correlation between the total F814W absolute magnitude of the ICL and the cluster velocity dispersion and mass. There is no apparent correlation between the cluster mass-to-light ratio (M/L) and the amount of ICL, and no evidence of any preferential orientation in the ICL source distribution. We find no strong variation in the amount of ICL between z = 0 and z = 0.8. In addition, we find wavelet-detected compact objects (WDCOs) in the three clusters for which data in two bands are available; these objects are probably very faint compact galaxies that in some cases are members of the respective clusters and comparable to the faint dwarf galaxies of the Local Group. Conclusions. We show that the ICL is prevalent in clusters at least up to redshift z = 0.8. In the future, we propose to detect the ICL at even higher redshifts, to determine wether there is a particular stage of cluster evolution where it was stripped from galaxies and spread into the intracluster medium.
Context. Large numbers of deep optical images will be available in the near future, allowing statistically significant studies of low surface brightness structures such as intracluster light (ICL) in galaxy clusters. The detection of these structures requires efficient algorithms dedicated to this task, which traditional methods find difficult to solve. Aims. We present our new detection algorithm with wavelets for intracluster light studies (DAWIS), which we developed and optimized for the detection of low surface brightness sources in images, in particular (but not limited to) ICL. Methods. DAWIS follows a multiresolution vision based on wavelet representation to detect sources. It is embedded in an iterative procedure called synthesis-by-analysis approach to restore the unmasked light distribution of these sources with very good quality. The algorithm is built so that sources can be classified based on criteria depending on the analysis goal. We present the case of ICL detection and the measurement of ICL fractions. We test the efficiency of DAWIS on 270 mock images of galaxy clusters with various ICL profiles and compare its efficiency to more traditional ICL detection methods such as the surface brightness threshold method. We also run DAWIS on a real galaxy cluster image, and compare the output to results obtained with previous multiscale analysis algorithms. Results. We find in simulations that DAWIS is on average able to separate galaxy light from ICL more efficiently, and to detect a greater quantity of ICL flux because of the way sky background noise is treated. We also show that the ICL fraction, a metric used on a regular basis to characterize ICL, is subject to several measurement biases on galaxies and ICL fluxes. In the real galaxy cluster image, DAWIS detects a faint and extended source with an absolute magnitude two orders brighter than previous multiscale methods.
O trabalho identifica as formas concretas e simbólicas de apropriação do espaço em uma empresa do setor de telecomunicações: a Telemig/Telemar-Minas. A disputa por espaços se liga ao sentido de territorialidade. Na medida em que os indivíduos defenderiam determinado espaço que lhes interessava, tais disputas envolveriam um amplo leque de dimensões como status e identidade, podendo refletir significações simbólicas que evidenciam relações de poder e dominação. Por meio de elementos da análise do discurso como instrumento metodológico básico para as análises sobre doze anos de atividades da empresa, observaram-se movimentos de desterritorialização e reterritorialização dos atores sociais envolvidos. Esses movimentos, somados às mudanças nas significações culturais, buscariam promover duas estratégias: a primeira, provocar um desenraizamento real e simbólico dos espaços; a segunda, tentar fazer com que a organização, por sua vez, apareça como um novo espaço de trabalho.
RESUMOste artigo procurou elaborar um encontro entre os estudos organizacionais e os temas cultura e espaço. Tem como objetivo evidenciar mudanças das significações culturais dos atores sociais da Reserva Particular do Patrimônio Natural (RPPN) Santuário do Caraça, em que parece existir um confronto entre esta ser um espaço religioso e um espaço turístico. Na abordagem empírica, procedeu-se um estudo de caso em que se procurou captar histórias, configurações, fronteiras, ambigüidades, enfim, expressões e significações de dirigentes e funcionários sobre suas próprias realidades. Embasado nas dimensões teóricas e na análise do discurso, este trabalho buscou estudar as diversas entrevistas não estruturadas, realizadas no período de novembro/2002 a junho/2003, no sentido de trazer à tona as mudanças das significações culturais. O Santuá-rio do Caraça e os atores que lá trabalham e vivem estão vendo suas histórias -significações, identidade, imagem -mudarem, assim como o espaço, que era apenas religioso e transforma-se em espaço turístico. ABSTRACThis article aimed at elaborating an encounter among Organizational Studies and themes such as culture and space. It has the objective of evidencing the changes occurred in the cultural significations of the social actor -Caraça Particular Reserve of the Natu ral Patrimony (RPPN -Reserva Particular do Patrimônio Natural Santuário do Caraça) -a place where an "opposition" seems to exist. Is RPPN a religious or a tourist place? The empirical approach of this research presents a case study, in which a search for the histories, configurations, frontiers and ambiguities takes place, in a way to prospect the expressions and significations of managers and employees about their own realities. Based on the theoretical dimensions and on the Discourse Analysis, the present article aimed at analyzing the diverse non-structured interviews that took place between November 2002 and July 2003, in order to feature the changes of the cultural significations. The Caraça Particular Reserve (RPPN), and the social actors that work there are seeing their history -significations, identities, images -modify right in front of their eyes. Previously, solely a religious site, the place is now attracting visitors, for being a tourist spot.
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