Lluvia polínica actual en el parque Nacional Lihue Calel, la Pampa, Argentina

Three years of modem pollen rain have been studied in the Parque Nacional Lihue Calel (La Pampa. Argentina) with Tauber traps. This study provides the interannual and seasonal variations in the pollen concentration, richness and diversity. Microscope analysis reveals 106 pollen types and 53 familias. The pollen spectra show the vegetation type of the Monte and it also shows local Pleridophyta spores. The Chenopodiaceae-Amaranthaceae represents the aloctone flora of surrounding regions of the Parle The first year had an atypical high pollen concentration. This was correlated with an abundant precipitation in the precedent winter. The seasonal pollen spectra showed a good correlation with flowering time of diverse species and with the pollen resources.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.) Presentado en la Asociación Paleontológica Argentina. Publicación Especial 6. X Simposio Argentino de Paleontologí

Variaciones de los espectros polínicos de miel y carga corbicular en un colmenar de Santa Rosa, La Pampa

In order to study the behavior between the hives in one apiary, the pollen spectra of pollen basket and honey samples were analyzed. The samples were taken at the same lime from five similar hives during 2 months. A total of 30 pollen types were Identified, 5 of them were found exclusively in pollen basket samples, 11 taxa in honey samples and 14 pollen types were common in both. Al both activities the colonies showed high selectivity and the bees preferred a few species called primary source (percentage higher than 10). The taxonomic richness, higher in honey than in pollen basket, was due lo pollution from different airborne pollen grains. The high values of correlation between pollen spectra of corbiculares and honeys, removed all the same lime from different hives, suggest a similar behavior in the explotation of vegetable resource. This uniformity shows that a few colonies may be used to provide a good representation of both activities in the whole apiary.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.) Presentado en las Jornadas Pampeanas de Ciencias Naturales, 1-3 de diciembre de 1999. Santa Rosa. La Pampa: 253-260

Estudio de la emisión polínica de un cultivo de girasol (Helianthus annuus L. )

The objective of this study was to estimate the pollen emission dynamics of the sunflower crop and its relationship with some environmental variables such as daily mean temperature (DMT) and precipitation. Two sunflower hybrids (ACA 884 and Cargill 5515) were sown under field conditions at the Facultad de Agronomía, La Pampa on 26/10/98. Meteorological data was obtained from an agrometeorological station located near the field experiment. Soil water content was measured al sowing time and its dynamic registered over time. Capitula population in the crop was measured before first anthesis took place. During the anthesis period the number of disc florets per capilulum was counted in randomly selected plants. To measure the production ot pollen grains per flower, florets still closed were taken from sectors of the capitula located at its periphery, middle and center. DMT controlled the flowering progress of both genotypes according with the maintenance or not of its value over the average temperature during the whole process. The total floret number was similar for both hybrids and the concentration of pollen grains per floret showed no difference between hybrids. Significant differences were however found between the sectors of the capitulum, being the peripheral one the most productive.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.) Presentado en VII Jornadas Pampeanas de Ciencias Naturales, 1-3 de diciembre de 1999. Santa Rosa. La Pampa: 105-113

SAURON's Challenge for the Major Merger Scenario of Elliptical Galaxy Formation

The intrinsic anisotropy delta and flattening epsilon of simulated merger remnants is compared with elliptical galaxies that have been observed by the SAURON collaboration, and that were analysed using axisymmetric Schwarzschild models. Collisionless binary mergers of stellar disks and disk mergers with an additional isothermal gas component, neglecting star formation cannot reproduce the observed trend delta = 0.55 epsilon (SAURON relationship). An excellent fit of the SAURON relationship for flattened ellipticals with epsilon >= 0.25 is however found for merger simulations of disks with gas fractions >= 20%, including star formation and stellar energy feedback. Massive black hole feedback does not strongly affect this result. Subsequent dry merging of merger remnants however does not generate the slowly-rotating SAURON ellipticals which are characterized by low ellipticities epsilon < 0.25 and low anisotropies. This indicates that at least some ellipticals on the red galaxy sequence did not form by binary mergers of disks or early-type galaxies. We show that stellar spheroids resulting from multiple, hierarchical mergers of star-bursting subunits in a cosmological context are in excellent agreement with the low ellipticities and anisotropies of the slowly rotating SAURON ellipticals and their observed trend of delta with epsilon. The numerical simulations indicate that the SAURON relation might be a result of strong violent relaxation and phase mixing of multiple, kinematically cold stellar subunits with the angular momentum of the system determining its location on the relation.Comment: 13 pages, 3 figures, submitted to Ap

The Formation of Disks in Elliptical Galaxies

We investigate detailed kinematical properties of simulated collisionless merger remnants of disk galaxies with mass ratios of 1:1 and 3:1. The simulations were performed by direct summation using the new special hardware device GRAPE-5. In agreement with observations, the shape of the line-of-sight velocity distribution (LOSVD) is Gaussian with small deviations. For most cases we find that the retrograde wings of the LOSVD are steeper than the prograde ones. This is in contradiction with observations which show broad retrograde and steep prograde wings. This serious problem in the collisionless formation scenario of massive elliptical galaxies can be solved if all rotating ellipticals, even boxy ones, contain an additional stellar disk component with $\propto 15$ of the total stellar mass and a scale length of order the effective radius of the spheroid. We propose that the progenitor galaxies of massive ellipticals must have contained a significant amount of gas that did not condense into stars during the merger process itself but formed an extended gaseous disk before the star formation epoch. The heating source that prevented the gas from forming stars early and the origin of the large specific angular momentum required for the gas component to form an extended disk are still unsolved problems.Comment: 16 pages, 4 figures, submitted to ApJ Letter

The SILCC (SImulating the LifeCycle of molecular Clouds) project: I. Chemical evolution of the supernova-driven ISM

The SILCC project (SImulating the Life-Cycle of molecular Clouds) aims at a more self-consistent understanding of the interstellar medium (ISM) on small scales and its link to galaxy evolution. We simulate the evolution of the multi-phase ISM in a 500 pc x 500 pc x 10 kpc region of a galactic disc, with a gas surface density of $\Sigma_{_{\rm GAS}} = 10 \;{\rm M}_\odot/{\rm pc}^2$. The Flash 4.1 simulations include an external potential, self-gravity, magnetic fields, heating and radiative cooling, time-dependent chemistry of H$_2$ and CO considering (self-) shielding, and supernova (SN) feedback. We explore SN explosions at different (fixed) rates in high-density regions (peak), in random locations (random), in a combination of both (mixed), or clustered in space and time (clustered). Only random or clustered models with self-gravity (which evolve similarly) are in agreement with observations. Molecular hydrogen forms in dense filaments and clumps and contributes 20% - 40% to the total mass, whereas most of the mass (55% - 75%) is in atomic hydrogen. The ionised gas contributes <10%. For high SN rates (0.5 dex above Kennicutt-Schmidt) as well as for peak and mixed driving the formation of H$_2$ is strongly suppressed. Also without self-gravity the H$_2$ fraction is significantly lower ($\sim$ 5%). Most of the volume is filled with hot gas ($\sim$90% within $\pm$2 kpc). Only for random or clustered driving, a vertically expanding warm component of atomic hydrogen indicates a fountain flow. Magnetic fields have little impact on the final disc structure. However, they affect dense gas ($n\gtrsim 10\;{\rm cm}^{-3}$) and delay H$_2$ formation. We highlight that individual chemical species, in particular atomic hydrogen, populate different ISM phases and cannot be accurately accounted for by simple temperature-/density-based phase cut-offs.Comment: 30 pages, 23 figures, submitted to MNRAS. Comments welcome! For movies of the simulations and download of selected Flash data see the SILCC website: http://www.astro.uni-koeln.de/silc

The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae

We study the impact of stellar winds and supernovae on the multi-phase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)$^2$ x $\pm$ 5 kpc and a gas surface density of 10 M$_{\odot}$/pc$^2$. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters which combine the winds from indi- vidual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-)shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters which have lower average masses (10$^2$ - 10$^{4.3}$ M$_{\odot}$) and form on shorter timescales (10$^{-3}$ - 10 Myr). In particular we find an anti-correlation of cluster mass and accretion time scale. Without winds the star clusters easily grow to larger masses for ~5 Myr until the first supernova explodes. Overall the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disk (mass loading $\gtrsim$ 1 at 1 kpc) can be launched by thermal gas pressure if more than 50% of the volume near the disc mid-plane can be heated to T > 3x10$^5$ K. Stellar winds alone cannot create a hot volume-filling phase. The models which are in best agreement with observed star formation rates drive either no outflows or weak outflows.Comment: 23 pages; submitted to MNRA

Mieles de la provincia de La Pampa. Origen botánico y su relación con el color

Se relaciona el origen botánico y el color en 148 muestras de miel de la Provincia de La Pampa, cosechadas entre 1990 y 1996. Las mieles predominantes, monoflorales, provienen de malezas típicas de áreas modificadas Como el abrepuño amarillo (Centaurea solstitislis), tréboles de olor (Melilotus spp.), mostacillas, nabos, flor amarilla (Brassicaceae), diversas especies de eucaliptos (Eucayptus spp.) utilizadas en forestación y especies nativas del monte o del caldenar, tales como algarrobo, caldén, alpataco (Prosopis spp.) y piquillln (Condalia microphylla). Existe una estrecha relación entre el origen botánico de mieles monofloras y sus colores respectivos. Los colores más claros se presentan en mieles de Centaurea solstitialis y Melilotus spp. y los más oscuros en mieles de Condalia microphylla. Las mieles de Eucalyptus spp. ofrecen en su mayoría una coloración ámbar claro y las de Prosopis spp. varían entre el extra blanco al ámbar extra claro. Las crucíferas originan mieles con un amplio rango en su coloración.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.). Presentado en Encuentro de Investigadores en temas relacionados a la Apicultura. Expomiel Azul'99, Área Temática Flora Apícola, 3 pág

Formation of early-type galaxies from cosmological initial conditions

We describe high resolution Smoothed Particle Hydrodynamics (SPH) simulations of three approximately $M_*$ field galaxies starting from \LCDM initial conditions. The simulations are made intentionally simple, and include photoionization, cooling of the intergalactic medium, and star formation but not feedback from AGN or supernovae. All of the galaxies undergo an initial burst of star formation at $z \approx 5$, accompanied by the formation of a bubble of heated gas. Two out of three galaxies show early-type properties at present whereas only one of them experienced a major merger. Heating from shocks and -PdV work dominates over cooling so that for most of the gas the temperature is an increasing function of time. By $z \approx 1$ a significant fraction of the final stellar mass is in place and the spectral energy distribution resembles those of observed massive red galaxies. The galaxies have grown from $z=1 \to 0$ on average by 25% in mass and in size by gas poor (dry) stellar mergers. By the present day, the simulated galaxies are old ($\approx 10 {\rm Gyrs}$), kinematically hot stellar systems surrounded by hot gaseous haloes. Stars dominate the mass of the galaxies up to $\approx 4$ effective radii ($\approx 10$ kpc). Kinematic and most photometric properties are in good agreement with those of observed elliptical galaxies. The galaxy with a major merger develops a counter-rotating core. Our simulations show that realistic intermediate mass giant elliptical galaxies with plausible formation histories can be formed from \LCDM initial conditions even without requiring recent major mergers or feedback from supernovae or AGN.Comment: accepted for publication in Ap

The Milky Way: An Exceptionally Quiet Galaxy; Implications for the formation of spiral galaxies

[Abridged]We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their relative locations in the planes formed by V_flat versus M_K, j_disk, and the average Fe abundance of stars in the galaxy outskirts. We find, for all relationships, that the MW is systematically offset by ~ 1 sigma, showing a significant deficiency in stellar mass, in angular momentum, in disk radius and [Fe/H] in the stars in its outskirts at a given V_flat. On the basis of their location in the M_K, V_flat, and R_d volume, the fraction of spirals like the MW is 7+/-1%, while M31 appears to be a "typical'' spiral. Our Galaxy appears to have escaped any significant merger over the last ~10 Gyrs which may explain why it is deficient by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity and then, unrepresentative of the typical spiral. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging. We conclude that the standard scenario of secular evolution is generally unable to reproduce the properties of most (if not all) spiral galaxies. However, the so-called "spiral rebuilding'' scenario proposed by Hammer et al. 2005 is consistent with the properties of both distant galaxies and of their descendants - the local spirals.Comment: 14 pages, 6 figures, to appear in Ap