The <i>Herschel</i> view of the massive star-forming region NGC 6334

Aims: Fundamental to any theory of high-mass star formation are gravity and turbulence. Their relative importance, which probably changes during cloud evolution, is not known. By investigating the spatial and density structure of the high-mass star-forming complex NGC 6334 we aim to disentangle the contributions of turbulence and gravity. Methods: We used Herschel PACS and SPIRE imaging observations from the HOBYS key programme at wavelengths of 160, 250, 350, and 500 μm to construct dust temperature and column density maps. Using probability distribution functions (PDFs) of the column density determined for the whole complex and for four distinct sub-regions (distinguished on the basis of differences in the column density, temperature, and radiation field), we characterize the density structure of the complex. We investigate the spatial structure using the Δ-variance, which probes the relative amount of structure on different size scales and traces possible energy injection mechanisms into the molecular cloud. Results: The Δ-variance analysis suggests that the significant scales of a few parsec that were found are caused by energy injection due to expanding HII regions, which are numerous, and by the lengths of filaments seen everywhere in the complex. The column density PDFs have a lognormal shape at low densities and a clearly defined power law at high densities for all sub-regions whose slope is linked to the exponent α of an equivalent spherical density distribution. In particular with α = 2.37, the central sub-region is largly dominated by gravity, caused by individual collapsing dense cores and global collapse of a larger region. The collapse is faster than free-fall (which would lead only to α = 2) and thus requires a more dynamic scenario (external compression, flows). The column density PDFs suggest that the different sub-regions are at different evolutionary stages, especially the central sub-region, which seems to be in a more evolved stage

Aquatic invertebrate's distribution in a freshwater coastal lagoon of southern Brazil in relation to water and sediment characteristics Distribuição de invertebrados aquáticos em uma lagoa costeira de água doce ao sul do Brasil em relação às características de água e sedimento

AIM: The objective of this study was to evaluate the influence of water and sediment characteristics on the abundance, richness and diversity of the benthic invertebrate community in Peri lagoon, a freshwater coastal lagoon located in central coast of Santa Catarina State; METHODS: Samplings were performed in April, May and June 2009, in five different sites of Peri lagoon. The samples were taken with an Eckman-Birge drag, totalizing 60 for the invertebrate community, and 45 for sediment. Water physicochemical variables were also measured. Environmental influences in benthic community have been measured using a Canonical Correspondence Analysis (CCA). Linear regressions were also plotted for main correlations; RESULTS: A total of 5,535 specimens were collected, identified into 18 taxa. Tanaidacea was the most abundant representing 54% of relative abundance, followed by Diptera (23%), and Ostracoda (17%). The richest family was Chironomidae with 6 taxa. CCA results indicated positive correlation between Chaoborus and Stenocypris with local depth, and negative correlation between Odonata, Gastropoda, Cytheridella and Coleoptera with the finest grains of sediment, as well as between Tanaidacea, Lopescladius, Annelida and Nematoda with both organic matter (OM) content in sediment and local depth. Linear regression analysis demonstrated inverse relation of Tanaidacea in response to OM (y = 0.6 - 0.62.OM) and sand (y = 0.6 - 0.6.sand), and of Lopescladius in response to OM (y = 0.37 - 0.41.OM) and sand (y = 0.37 - 0.46.sand). The fact that Peri lagoon has no marine influence and has Tanaidacea as the most abundant taxa, a group not expected in freshwaters, gives to this lagoon a particular relevance among coastal lagoons. The study concluded that sediment characteristics and local depth are more significant than water variables in determining the benthic community structure in Peri lagoon, which varied in accordance with different local conditions.<br>OBJETIVO: O objetivo deste estudo foi avaliar a influência das características da água e sedimento na abundância, diversidade e riqueza da comunidade de invertebrados bentônicos na lagoa do Peri, uma lagoa costeira de água doce localizada em Santa Catarina. MÉTODOS: Foram realizadas 60 coletas para análise de invertebrados, e 45 para sedimento entre abril, maio e junho de 2009, em 5 diferentes pontos da lagoa com draga Eckman-Birge. Variáveis físicas e químicas da água também foram medidas. A influência dos fatores ambientais na comunidade foi medida através de uma Análise de Correspondência Canônica (CCA), e foram feitas regressões lineares para as principais correlações; RESULTADOS: Um total de 5,535 espécimes foram coletados, identificados em 18 táxons. Tanaidacea foi o mais abundante representando 54% da abundância relativa, seguido de Diptera (23%) e Ostracoda (17%). A família mais rica em gêneros foi Chironomidae (6 táxons). Os resultados da CCA revelaram correlação positiva entre Chaoborus e Stenocypris com a profundidade local, e negativa entre Odonata, Gastropoda, Cytheridella e Coleoptera com grãos finos, assim como entre Tanaidacea, Lopescladius, Annelida e Nematoda com a quantidade de matéria orgânica (MO) no sedimento e profundidade local. Regressões lineares demonstraram uma relação inversa de Tanaidacea em resposta a MO (y = 0.6 - 0.62.MO) e areia grossa (y = 0.6 - 0.6.are) assim como de Lopescladius em relação a MO (y = 0.37 - 0.41.MO) e areia grossa (y = 0.37 - 0.46.are). O fato da lagoa do Peri não ter influência do mar e ter Tanaidacea como táxon mais abundante, um grupo não esperado em ambientes de água doce, lhe confere destaque entre demais lagoas costeiras do Brasil. Através deste estudo concluímos que as características de sedimento e profundidade local foram mais importantes que variáveis da água na determinação da estrutura da comunidade de invertebradoss bentônicos na lagoa do Peri, que variou de acordo com características ambientais locais