Moving frontiers in the Amazon. Brazilian small-scale gold miners in Suriname

This article explores the national, local, and personal frontiers that Brazilian small-scale gold miners – called garimpeiros – cross in their quest for gold in the larger Amazon region. Ethnographic research was conducted among garimpeiros and mining service providers in Suriname. In the past three decades, thousands of Brazilian migrants have entered Suriname and consequently affected its society, economy, and culture. It is argued that in the absence of strong state control, these garimpeiros, along with local forest peoples and legal title holders, are traversing the fluctuating boundaries. These boundaries include national borders, customary and legal regulations, technological limitations, and personal livelihood goals. The continuous reformulation of these multiple boundaries drives the development of local mining cultures. Social networks increase the volatility of formal and informal borders, and are the key to these mining cultures as well. The authors conclude that while entering Suriname and its gold mines is relatively easy, financial and conceptual barriers often prevent miners from leaving.Resumen: Fronteras fluctuantes en el Amazonas: los mineros artesanales de oro en SurinameEste artículo explora las fronteras nacionales, locales y personales que cruzan los garimpeiros (como se llama a los mineros brasileños que trabajan explotaciones auríferas a pequeña escala) en su búsqueda de oro en la región amazónica. La investigación etnográfica en que se basa este artículo se realizó entre garimpeiros y proveedores de servicios para la minería en Suriname. En las últimas tres décadas, miles de inmigrantes brasileños han llegado a Suriname y afectado su sociedad, economía y cultura. En el artículo se sostiene que en ausencia de un control estatal fuerte, los garimpeiros, junto con grupos indígenas locales y tenedores de tierra legítimos, cruzan estas fronteras fluctuantes, que incluyen las fronteras nacionales, las regulaciones aduaneras y legales, las limitaciones tecnológicas y los objetivos de supervivencia personal. Esta continua reformulación de fronteras múltiples sostiene el desarrollo de las culturas mineras locales. Las redes sociales aumentan la volatilidad de las fronteras formales e informales, y son de crucial importancia para estas culturas mineras. Los autores concluyen que aunque entrar a Suriname y a sus minas de oro es relativamente fácil, las barreras conceptuales y económicas a menudo impiden que los mineros vuelvan a casa

HST Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Modeling the Lens

We investigate gravitational lens models for the quadruply-lensed Cloverleaf BAL QSO H1413+1143 based on the HST WFPC/WFPC2 astrometric and photometric data of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The accurate image positions and the dust-extinction-corrected relative amplifications, along with a possible detection of the lensing galaxy in the infrared, permit more accurate lens models than were previously possible. While more recent models are qualitatively consistent with the HST data, none of the previous models considered the dust-extinction-corrected relative amplifications of the image components. We use the power-law elliptical mass model to fit the HST data. We find that a single elliptical galaxy perturbed by an external shear can fit the image positions within the observational uncertainties; however, the predicted relative magnifications are only roughly consistent with the observational relative amplifications. We find that a primary galaxy combined with a secondary galaxy in the vicinity of the Cloverleaf or a cluster centered (south-)west of the Cloverleaf can fit both the image positions and relative amplifications within the observational uncertainties. We discuss future observations which could be used to test and/or further constrain lens models of the Cloverleaf.Comment: 23 pages (in aaspp.sty) including 5 tables and 3 figures, Accepted for publication in the Astrophysical Journa

Cluster Ellipticities as a Cosmological Probe

We investigate the dependence of ellipticities of clusters of galaxies on cosmological parameters using large-scale cosmological simulations. We determine cluster ellipticities out to redshift unity for LCDM models with different mean densities $\Omega_m$ and amplitudes of mass fluctuation $\sigma_{8,0}$. The mean ellipticity increases monotonically with redshift for all models. Larger values of $\sigma_{8,0}$, i.e., earlier cluster formation time, produce lower ellipticities. The dependence of ellipticity on $\Omega_m$ is relatively weak in the range $0.2 \leq \Omega_m \leq 0.5$ for high mass clusters. The mean ellipticity $\bar{e}(z)$ decreases linearly with the amplitude of fluctuations at the cluster redshift $z$, nearly independent of $\Omega_m$; on average, older clusters are more relaxed and are thus less elliptical. The distribution of ellipticities about the mean is approximated by a Gaussian, allowing a simple characterization of the evolution of ellipticity with redshift as a function of cosmological parameters. At $z=0$, the mean ellipticity of high mass clusters is approximated by $\bar{e}(z=0) = 0.248-0.069 \sigma_{8,0} + 0.013 \Omega_{m,0}$. This relation opens up the possibility that, when compared with future observations of large cluster samples, the mean cluster ellipticity and its evolution could be used as a new, independent tool to constrain cosmological parameters, especially the amplitude of mass fluctuations, $\sigma_{8,0}$.Comment: 16 pages, 4 figure

Cluster Alignments and Ellipticities in LCDM Cosmology

The ellipticities and alignments of clusters of galaxies, and their evolution with redshift, are examined in the context of a Lambda-dominated cold dark matter cosmology. We use a large-scale, high-resolution N-body simulation to model the matter distribution in a light cone containing ~10^6 clusters out to redshifts of z=3. Cluster ellipticities are determined as a function of mass, radius, and redshift, both in 3D and in projection. We find strong cluster ellipticities: the mean ellipticity increases with redshift from 0.3 at z=0 to 0.5 at z=3, for both 3D and 2D ellipticities; the evolution is well-fit by e=0.33+0.05z. The ellipticities increase with cluster mass and with cluster radius; the main cluster body is more elliptical than the cluster cores, but the increase of ellipticities with redshift is preserved. Using the fitted cluster ellipsoids, we determine the alignment of clusters as a function of their separation. We find strong alignment of clusters for separations <100 Mpc/h; the alignment increases with decreasing separation and with increasing redshift. The evolution of clusters from highly aligned and elongated systems at early times to lower alignment and elongation at present reflects the hierarchical and filamentary nature of structure formation. These measures of cluster ellipticity and alignment will provide a new test of the current cosmological model when compared with upcoming cluster surveys.Comment: 29 pages including 13 figures, to appear in ApJ Jan. 2005 (corrected typos, added reference