Evaluación de la calidad de agua del Río Tercero (Ctalamochita)

El Río Tercero, o Ctalamochita, es uno de los más caudalosos y utilizados de la Provincia de Córdoba. En su recorrido pasa por grandes ciudades, donde recibe descargas de industrias y efluentes cloacales. Se eligieron los sitios antes de las ciudades más importantes y aguas abajo de las mismas, incluyendo de esta forma las descargas cloacales y de las industrias ubicadas cerca del río. Los sitios seleccionados fueron: al comienzo del nacimiento del río, en la ciudad de Río Tercero, aguas debajo de esta ciudad, antes y después de Villa María, en el balneario de Bell Ville y al finalizar el recorrido del río en el Club Matienzo de la localidad de Saladillo En este trabajo se caracterizó la calidad del agua del Río Ctalamochita o Tercero, a través de diferentes herramientas estadísticas y mediante el uso del Índice de Calidad de Agua (ICA). Para ello se utilizaron los parámetros clásicos de monitoreo; físicos, químicos y bacteriológicos medidos en agua desde el año 2005 al 2009. Estos datos se analizaron utilizando estadística descriptiva, el Índice de Calidad de Agua (ICA), y análisis multivariado. Los resultados de estos análisis evidenciaron el deterioro que sufre el río al atravesar las grandes ciudades, como Villa María y Bell Ville. Estas diferencias son explicadas por algunas variables entre las que se destaca el aumento del contenido de fósforo total aguas abajo de las mencionadas ciudades.Fil: O’Mill, Patricia. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas; Argentina.Fil: O’Mill, Patricia. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: O’Mill, Patricia. Secretaría de Recursos Hídricos y Coordinación; Argentina.Fil: Amé, María Valeria. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas; Argentina.Fil: Cosavella, Ana María. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Cosavella, Ana María. Secretaría de Recursos Hídricos y Coordinación; Argentina.Fil: Larrosa, Nancy. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Carranza, Patricia. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Otras Ingeniería del Medio Ambient

Galaxy interactions I: Major and minor mergers

We study galaxy pair samples selected from the Sloan Digital Sky Survey (SDSS-DR7) and we perform an analysis of minor and major mergers with the aim of investigating the dependence of galaxy properties on interactions. We build a galaxy pair catalog requiring rp < 25 kpc h-1 and Delta V < 350 km s-1 within redshift z<0.1. By visual inspection of SDSS images we removed false identifications and we classify the interactions into three categories: pairs undergoing merging, M; pairs with evident tidal features, T; and non disturbed, N. We also divide the pair sample into minor and major interactions according to the luminosity ratio of the galaxy members. We study star formation activity through colors and star formation rates. We find that 10% of the pairs are classified as M. These systems show an excess of young stellar populations as inferred from the Dn(4000) spectral index, colors, and star formation rates of the member galaxies, an effect which we argue, is directly related to the ongoing merging process. We find 30% of the pairs exhibiting tidal features (T pairs) with member galaxies showing evidence of old stellar populations. Regardless of the color distribution, we find a prominent blue peak in the strongest mergers, while pairs with tidal signs under a minor merger show a strong red peak. Therefore, our results show that galaxy interactions are important in driving the evolution of galaxy bimodality. By adding stellar masses and star formation rates of the two members of the pairs, we explore the global efficiency of star formation of the pairs as a whole. We find that, at a given total stellar mass, major mergers are significantly more efficient (a factor 2) in forming new stars, with respect to both minor mergers or a control sample of non-interacting galaxies.Comment: 10 pages, 14 figures, submitted to A&

Measures of Galaxy Environment - I. What is "Environment"?

The influence of a galaxy's environment on its evolution has been studied and compared extensively in the literature, although differing techniques are often used to define environment. Most methods fall into two broad groups: those that use nearest neighbours to probe the underlying density field and those that use fixed apertures. The differences between the two inhibit a clean comparison between analyses and leave open the possibility that, even with the same data, different properties are actually being measured. In this work we apply twenty published environment definitions to a common mock galaxy catalogue constrained to look like the local Universe. We find that nearest neighbour-based measures best probe the internal densities of high-mass haloes, while at low masses the inter-halo separation dominates and acts to smooth out local density variations. The resulting correlation also shows that nearest neighbour galaxy environment is largely independent of dark matter halo mass. Conversely, aperture-based methods that probe super-halo scales accurately identify high-density regions corresponding to high mass haloes. Both methods show how galaxies in dense environments tend to be redder, with the exception of the largest apertures, but these are the strongest at recovering the background dark matter environment. We also warn against using photometric redshifts to define environment in all but the densest regions. When considering environment there are two regimes: the 'local environment' internal to a halo best measured with nearest neighbour and 'large-scale environment' external to a halo best measured with apertures. This leads to the conclusion that there is no universal environment measure and the most suitable method depends on the scale being probed.Comment: 14 pages, 9 figures, 1 table, published in MNRA

Close galaxy pairs with accurate photometric redshifts

Context. Studies of galaxy pairs can provide valuable information to jointly understand the formation and evolution of galaxies and galaxy groups. Consequently, taking the new high-precision photo-z surveys into account, it is important to have reliable and tested methods that allow us to properly identify these systems and estimate their total masses and other properties. Aims. In view of the forthcoming Physics of the Accelerating Universe Survey (PAUS), we propose and evaluate the performance of an identification algorithm of projected close isolated galaxy pairs. We expect that the photometrically selected systems can adequately reproduce the observational properties and the inferred lensing mass–luminosity relation of a pair of truly bound galaxies that are hosted by the same dark matter halo. Methods. We developed an identification algorithm that considers the projected distance between the galaxies, the projected velocity difference, and an isolation criterion in order to restrict the sample to isolated systems. We applied our identification algorithm using a mock galaxy catalog that mimics the features of PAUS. To evaluate the feasibility of our pair finder, we compared the identified photometric samples with a test sample that considers that both members are included in the same halo. Taking advantage of the lensing properties provided by the mock catalog, we also applied a weak-lensing analysis to determine the mass of the selected systems. Results. Photometrically selected samples tend to show high purity values, but tend to misidentify truly bounded pairs as the photometric redshift errors increase. Nevertheless, overall properties such as the luminosity and mass distributions are successfully reproduced. We also accurately reproduce the lensing mass–luminosity relation as expected for galaxy pairs located in the same halo

Herschel-ATLAS/GAMA : the environmental density of far-infrared bright galaxies at z < 0.5

We compare the environmental and star formation properties of far-infrared detected and non-far-infrared detected galaxies out to z similar to 0.5. Using optical spectroscopy and photometry from the Galaxy And Mass Assembly (GAMA) and Sloan Digital Sky Survey, with far-infrared observations from the Herschel Astrophysical Terahertz Large Area Survey (ATLAS) Science Demonstration Phase, we apply the technique of Voronoi tessellations to analyse the environmental densities of individual galaxies. Applying statistical analyses to colour, r-band magnitude and redshift-matched samples, we show that there is a significant difference at the 3.5 Sigma level between the normalized environmental densities of these two populations. This is such that infrared emission (a tracer of star formation activity) favours underdense regions compared to those inhabited by exclusively optically observed galaxies selected to be of the same r-band magnitude, colour and redshift. Thus, more highly star-forming galaxies are found to reside in the most underdense environments, confirming previous studies that have proposed such a correlation. However, the degeneracy between redshift and far-infrared luminosity in our flux-density-limited sample means that we are unable to make a stronger statement in this respect. We then apply our method to synthetic light cones generated from semi-analytic models, finding that over the whole redshift distribution the same correlations between star formation rate and environmental density are found.Peer reviewe