Complete Zeldovich approximation

We have developed a generalization of the Zeldovich approximation (ZA) that is exact in a wide variety of situations, including plannar, spherical and cilyndrical symmetries. We have shown that this generalization, that we call complete Zeldovich approximation (CZA), is exact to second order at an arbitrary point within any field. For gaussian fields, the third order error have been obtained and shown to be very small. For statistical purposes, the CZA leads to results exact to the third order.Comment: 11 pages+1 figure, accepted in ApJ Letter

Fluctuations of K-band galaxy counts

We measure the variance in the distribution of off-plane (|b|>20 deg.) galaxies with m_K<13.5 from the 2MASS K-band survey in circles of diameter between 0.344 deg. and 57.2 deg. The use of a near-infrared survey makes negligible the contribution of Galactic extinction to these fluctuations. We calculate these variances within the standard Lambda-CDM model assuming that the sources are distributed like halos of the corresponding mass, and it reproduces qualitatively the galaxy counts variance. Therefore, we test that the counts can be basically explained in terms only of the large scale structure. A second result of this paper is a new method to determine the two point correlation function obtained by forcing agreement between model and data. This method does not need the knowledge of the two-point angular correlation function, allows an estimation of the errors (which are low with this method), and can be used even with incomplete surveys. Using this method we get xi(z=0, r<10 h^{-1}Mpc)=(29.8+/-0.3) (r/h^{-1}Mpc)^{-1.79+/-0.02}, which is the first measure of the amplitude of xi in the local Universe for the K-band. It is more or less in agreement with those obtained through red optical filters selected samples, but it is larger than the amplitude obtained for blue optical filters selected samples.Comment: 7 pages, 5 figures, accepted to be published in A&

Probability distribution of density fluctuations in the non-linear regime

We present a general procedure for obtaining the present density fluctuation probability distribution given the statistics of the initial conditions. The main difficulties faced with regard to this problem are those related to the non-linear evolution of the density fluctuations and those posed by the fact that the fields we are interested in are the result of filtering an underlying field with structure down to scales much smaller than that of filtering. The solution to the latter problem is discussed here in detail and the solution to the former is taken from a previous work. We have checked the procedure for values of the rms density fluctuation as large as 3/2 and several power spectra and found that it leads to results in excellent agreement with those obtained in numerical simulations. We also recover all available exact results from perturbation theory.Comment: Accepted to be published in Ap

Generation of galactic disc warps due to intergalactic accretion flows onto the disc

A new method is developed to calculate the amplitude of the galactic warps generated by a torque due to external forces. This takes into account that the warp is produced as a reorientation of the different rings which constitute the disc in order to compensate the differential precession generated by the external force, yielding a uniform asymptotic precession for all rings. Application of this method to gravitational tidal forces in the Milky Way due to the Magellanic Clouds leads to a very low amplitude of the warp. If the force were due to an extragalactic magnetic field, its intensity would have to be very high, to generate the observed warps. An alternative hypothesis is explored: the accretion of the intergalactic medium over the disk. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shape warp. The torque produced by a flow of velocity ~100 km/s and baryon density \~10^{-25} kg/m^3 is enough to generate the observed warps and this mechanism offers quite a plausible explanation. First, because this order of accretion rate is inferred from other processes observed in the Galaxy, notably its chemical evolution. The inferred rate of infall of matter, ~1 solar-mass/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of this chemical evolution resolving key issues, notably the G-dwarf problem. Second, because the required density of the intergalactic medium is within the range of values compatible with observation. By this mechanism, we can explain the warp phenomenon in terms of intergalactic accretion flows onto the disk of the galaxy.Comment: 18 pages, 11 figures, accepted to be published in A&

The spherical collapse model with shell crossing

In this work, we study the formation and evolution of dark matter halos by means of the spherical infall model with shell-crossing. We present a framework to tackle this effect properly based on the numerical follow-up, with time, of that individual shell of matter that contains always the same fraction of mass with respect to the total mass. In this first step, we do not include angular momentum, velocity dispersion or triaxiality. Within this framework - named as the Spherical Shell Tracker (SST) - we investigate the dependence of the evolution of the halo with virial mass, with the adopted mass fraction of the shell, and for different cosmologies. We find that our results are very sensitive to a variation of the halo virial mass or the mass fraction of the shell that we consider. However, we obtain a negligible dependence on cosmology. Furthermore, we show that the effect of shell-crossing plays a crucial role in the way that the halo reaches the stabilization in radius and the virial equilibrium. We find that the values currently adopted in the literature for the actual density contrast at the moment of virialization, delta_vir, may not be accurate enough. In this context, we stress the problems related to the definition of a virial mass and a virial radius for the halo. The question of whether the results found here may be obtained by tracking the shells with an analytic approximation remains to be explored.Comment: 15 pages, 4 figures, 9 tables, replaced to match the published MNRAS versio

Quantifying the coherent outflows of galaxies around voids in the SDSS DR7

We report the detection, with a high level of confidence, of coherent outflows around voids found in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7). In particular, we developed a robust statistical test to quantify the strength of redshift-space distortions (RSD) associated with extended coherent velocity fields. We consistently find that the vector that joins void centers with galaxies that lie in shells around them is more likely to be perpendicular to the line-of-sight than parallel to it. This effect is clear evidence for the existence of outflows in the vicinity of voids. We show that the RSD exist for a wide range of void radius and shell thickness, but they are more evident in the largest voids in our sample. For instance, we find that the for galaxies located in shells within 2 h^-1 Mpc from the edge of voids larger than 15 h^-1 Mpc deviates 3.81sigma from uniformity. The measurements presented in this work provide useful information to constrain cosmological parameters, in particular Omega_m and Sigma_8.Comment: 4 pages, 1 figure, to appear in A&A Letter

Adiciones para la flora de Tenerife (Islas Canarias, España)

Additions to the flora of Tenerife (Canary Islands, Spain).- Recent fieldwork in Tenerife, especially in September 2010, yielded several interesting new records of non-native vascular plants. Bothriochloa ischaemum var. songarica, “Asian” Cardamine flexuosa, Cestrum parqui, Digitaria violascens, Ficus lyrata, Ficus rubiginosa, Hoffmannseggia glauca, Hyparrhenia rufa subsp. altissima, Jacaranda mimosifolia, Merremia tuberosa, Passiflora morifolia, Phytolacca dioica, Schefflera actinophylla and Solanum abutiloides are reported for the first time from the Canary Islands, while Eragrostis barrelieri var. pygmaea, Ficus microcarpa, Ipomoea purpurea, Leucaena leucocephala subsp. glabrata, Sechium edule, Tradescantia zebrina and Turnera ulmifolia are new to the flora of the island of Tenerife. New records of Acacia cyclops, Atriplex suberecta, Heliotropium curassavicum, Paspalum dilatatum, P. notatum, Pluchea ovalis, Pulicaria paludosa, Sclerophylax spinescens and Solanum villosum subsp. miniatum confirm their recent expansion on the island of Tenerife. New records are provided for the recently described Sporobolus copei . Finally, Paspalum vaginatum (hitherto possibly confused with P. distichum) and Potentilla indica are confirmed from the island of Tenerife.Adiciones para la flora de Tenerife (Islas Canarias, España).- Algunos recientes trabajos de campo en Tenerife, especialmente en Septiembre de 2010, trajeron consigo varias nuevas e interesantes adiciones de plantas vasculares no autóctonas. Bothriochloa ischaemum var. songarica, Cardamine flexuosa “Asiática”, Cestrum parqui, Digitaria violascens, Ficus lyrata, Ficus rubiginosa, Hoffmannseggia glauca, Hyparrhenia rufa subsp. altissima, Jacaranda mimosifolia, Merremia tuberosa, Passiflora morifolia, Phytolacca dioica, Schefflera actinophylla y Solanum abutiloides son citadas por primera vez para las islas Canarias mientras que Eragrostis barrelieri var. pygmaea, Ficus microcarpa, Ipomoea purpurea, Leucaena leucocephala subsp. glabrata, Sechium edule, Tradescantia zebrina y Turnera ulmifolia son nuevas para la flora de la isla de Tenerife. Nuevas localidades para Acacia cyclops, Atriplex suberecta, Heliotropium curassavicum, Paspalum dilatatum, P. notatum, Pluchea ovalis, Pulicaria paludosa, Sclerophylax spinescens y Solanum villosum subsp. miniatum confirman su reciente expansión en la isla de Tenerife. También se recogen nuevas localidades para el recientemente descrito Sporobolus copei. Finalmente, se confirma para la isla de Tenerife Paspalum vaginatum (hasta ahora posiblemente confundido con P. distichum) y Potentilla indica

Los peces (Chondrichthyes, Osteichthyes) del Plioceno inferior de Gran Canaria y Fuerteventura (Islas Canarias, España)

Fossil fish teeth are contained in marine deposits dated at ca 4.8 Ma found on the islands of Gran Canaria and Fuerteventura (Canary Islands, Spain). These islands, situated in the North Atlantic Subtropical Gyre, can be considered a mid-way stopover point between the Caribbean Sea, with the Central American Seaway about to close in this epoch, and the Mediterranean, in the first stage of its post-Messinian Gibraltar Seaway period. Accordingly, there existed extensive pantropical communication, particularly for nektonic animals capable of travelling large distances. In this paper, we present a number of fossil fishes, most of which are identified for the first time on the basis of their teeth: the Chondrichthyes species Carcharocles megalodon, Parotodus benedeni, Cosmopolitodus hastalis, Isurus oxyrinchus, Carcharias cf. acutissima, Carcharhinus cf. leucas, Carcharhinus cf. priscus, Galeocerdo cf. aduncus, and the Osteichthyes species Archosargus cinctus, Labrodon pavimentatum, and Diodon scillae. Coincidences are observed between these ichthyofauna and specimens found in the Azores Islands, the Pacific coast of America and the Mediterranean Sea.Los dientes fósiles de peces están contenidos en depósitos marinos datados en ca 4.8 Ma de las Islas de Gran Canaria y Fuerteventura (Islas Canarias, España). Estas islas, situadas en el Giro subtropical del Atlántico Norte, pueden considerarse una estación intermedia entre un Mar Caribe que estaba cercano al cierre del Paso de América Central, y el Mediterráneo en su primera etapa tras la apertura post-Mesiniense de Gibraltar. Ello permitía una comunicación pantropical para los animales del necton que eran capaces de desplazarse a grandes distancias. Se identifican por primera vez los peces Chondrichthyes Carcharocles megalodon, Parotodus benedeni, Cosmopolitodus hastalis, Isurus oxyrinchus, Carcharias cf. acutissima, Carcharhinus cf. leucas, Carcharhinus cf. priscus, Galeocerdo cf. aduncus y las species de Osteichthyes Archosargus cinctus, Labrodon pavimentatum y Diodon scillae. Se ha observado coincidencia entre los ejemplares canarios y los encontrados en las Islas Azores, las costas pacíficas de América y el mar Mediterráneo