Towards a Concordant Model of Halo Occupation Statistics

We use the conditional luminosity function (CLF) and data from the 2dFGRS to constrain the average relation between light and mass in a LCDM cosmology with Omega_m=0.23 and sigma_8=0.74 (hereafter WMAP3 cosmology). Reproducing the observed luminosity dependence of the galaxy two-point correlation function results in average mass-to-light ratios that are about 35 percent lower than in a LCDM cosmology with Omega_m=0.3 and sigma_8=0.9 (hereafter WMAP1 cosmology). This removes an important problem with previous halo occupation models which had a tendency to predict cluster mass-to-light ratios that were too high. For the WMAP3 cosmology our model yields average mass-to-light ratios, central galaxy luminosities, halo occupation numbers, satellite fractions, and luminosity-gap statistics, that are all in excellent agreement with those obtained from a 2dFGRS group catalogue and from other independent studies. We also use our CLF model to compute the probability distribution P(M|L_cen), that a central galaxy of luminosity L_cen resides in a halo of mass M. We find this distribution to be much broader than what is typically assumed in HOD models, which has important implications for the interpretation of galaxy-galaxy lensing data. Finally, reproducing the luminosity dependence of the pairwise velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios for clusters and a satellite fraction that decreases strongly with increasing luminosity. This is only marginally consistent with our CLF constraints. We argue that a cosmology with parameters between those of the WMAP1 and WMAP3 cosmologies is likely to yield results with a higher level of consistency.Comment: 23 pages, 11 figures. Submitted for publication in MNRA

The Luminosity, Colour and Morphology dependence of galaxy filaments in the Sloan Digital Sky Survey Data Release Four

We have tested for luminosity, colour and morphology dependence of the degree of filamentarity in seven nearly two dimensional strips from the Sloan Digital Sky Survey Data Release Four (SDSS DR4). The analysis is carried out at various levels of coarse graining allowing us to address different length-scales. We find that the brighter galaxies have a less filamentary distribution than the fainter ones at all levels of coarse graining. The distribution of red galaxies and ellipticals shows a higher degree of filamentarity compared to blue galaxies and spirals respectively at low levels of coarse graining. The behaviour is reversed at higher levels of coarse graining. We propose a picture where the ellipticals are densely distributed in the vicinity of the nodes where the filaments intersect while the spirals are sparsely distributed along the entire extent of the filaments. Our findings indicate that the regions with an excess of ellipticals are larger than galaxy clusters, protruding into the filaments. We have also compared the predictions of a semi-analytic model of galaxy formation (the Millennium Run galaxy catalogue) against our results for the SDSS. We find the two to be in agreement for the $M^{*}$ galaxies and for the red galaxies, while the model fails to correctly predict the filamentarity of the brighter galaxies and the blue galaxies.Comment: 14 Pages, 2 tables, 11 figures, Accepted for publication in MNRAS, new section added for a comparison with semi analytical models of galaxy formation, substantial revisio

The Three-Point Correlation Function in Cosmology

With the advent of high-quality surveys in cosmology the full three-point correlation function will be a valuable statistic for describing structure formation models. It contains information on cosmological parameters and detailed halo properties that cannot be extracted from the two-point correlation function. We use the halo clustering model to analytically calculate the three-point correlation function (3PCF) for general cosmological fields. We present detailed results for the configuration dependence of the 3-dimensional mass and galaxy distributions and the 2-dimensional cosmic shear field. We work in real space, where higher order correlation functions on small scales are easier to measure and interpret, but halo model calculations get rapidly intractable. Hence we develop techniques for accurate evaluations of the 1, 2 and 3-halo contributions to the 3PCF. The 3PCF violates the hierarchical ansatz in both its scale and configuration dependence. We study the behavior of the coefficient Q in the hierarchical expansion from large, quasilinear scales down to about 20 kpc. We find that the nonlinear 3PCF is sensitive to the halo profile of massive halos, especially its inner slope. We model the distribution of galaxies in halos and show that the 3PCF of red galaxies has a weaker configuration and scale dependence than the mass, while for blue galaxies it is very sensitive to the parameters of the galaxy formation model. The 3PCF from weak lensing on the other hand shows different scalings due to projection effects and a sensitivity to cosmological parameters.Comment: 30 pages, 23 figures, matches final version (minor changes) to appear in MNRA

SDSS J0903+5028: A New Gravitational Lens

We report the discovery of a new gravitationally lensed quasar from the Sloan Digital Sky Survey, SDSS J090334.92+502819.2. This object was targeted for SDSS spectroscopy as a Luminous Red Galaxy (LRG), but manual examination of the spectrum showed the presence of a quasar at z= 3.6 in addition to a red galaxy at z=0.388, and the SDSS image showed a second possible quasar image nearby. Follow-up imaging and spectroscopy confirmed the lensing hypothesis. In images taken at the ARC 3.5-meter telescope, two quasars are separated by 2.8 arc-seconds; the lensing galaxy is clearly seen and is blended with one of the quasar images. Spectroscopy taken at the Keck II telescope shows that the quasars have identical redshifts of z=3.6 and both show the presence of the same broad absorption line-like troughs. We present simple lens models which account for the geometry and magnifications. The lens galaxy lies near two groups of galaxies and may be a part of them. The models suggest that the groups may contribute considerable shear and may have a strong effect on the lens configuration.Comment: submitted to the Astronomical Journal. 27 pages, 7 figure

Cosmological parameters from lensing power spectrum and bispectrum tomography

We examine how lensing tomography with the bispectrum and power spectrum can constrain cosmological parameters and the equation of state of dark energy. Our analysis uses the full information at the two- and three-point level from angular scales of a few degrees to 5 arcminutes (50 < l < 3000), which will be probed by lensing surveys. We use all triangle configurations, cross-power spectra and bispectra constructed from up to three redshift bins with photometric redshifts, and relevant covariances in our analysis. We find that the parameter constraints from bispectrum tomography are comparable to those from power spectrum tomography. Combining the two improves parameter accuracies by a factor of three due to their complementarity. For the dark energy parameterization w(a) = w0 + wa(1-a), the marginalized errors from lensing alone are sigma(w0) = 0.03 fsky^{-1/2} and sigma(wa) = 0.1 fsky^{-1/2}. We show that these constraints can be further improved when combined with measurements of the cosmic microwave background or Type Ia supernovae. The amplitude and shape of the mass power spectrum are also shown to be precisely constrained. We use hyper-extended perturbation theory to compute the nonlinear lensing bispectrum for dark energy models. Accurate model predictions of the bispectrum in the moderately nonlinear regime, calibrated with numerical simulations, will be needed to realize the parameter accuracy we have estimated. Finally, we estimate how well the lensing bispectrum can constrain a model with primordial non-Gaussianity.Comment: 19 pages, 10 figures. Corrected typo in Equations (10) and (14). Added the joint parameter forecasts from lensing, CMB and Type Ia supernovae (Figures 8 and 9

PTHalos: A fast method for generating mock galaxy distributions

Current models of galaxy formation applied to understanding the large-scale structure of the universe have two parts. The first is an accurate solution of the equations of motion for the dark matter due to gravitational clustering. The second consists of making physically reasonable approximations to the behavior of baryons inside dark matter halos. The first uses large, computationally intensive, $n$-body simulations. We argue that because the second step is, at least at present, uncertain, it is possible to obtain similar galaxy distributions without solving the first step exactly. We describe an algorithm which is several orders of magnitude faster than n-body simulations, but which is, nevertheless, rather accurate. The algorithm combines perturbation theory with virialized halo models of the nonlinear density and velocity fields. For two- and three-point statistics the resulting fields are exact on large scales, and rather accurate well into the nonlinear regime, particularly for two-point statistics in real and redshift space. We then show how to use this algorithm to generate mock galaxy distributions from halo occupation numbers. As a first application, we show that it provides a good description of the clustering of galaxies in the PSCz survey. We also discuss applications to the estimation of non-Gaussian contributions to error bars and covariance matrix of the power spectrum, in real and redshift space, for galaxies and dark matter. The results for the latter show good agreement with simulations, supporting the use of our method to constrain cosmological parameters from upcoming galaxy surveys.Comment: 13 pages, 10 figures. (references added

Direct and indirect effects of soil fauna, fungi and plants on greenhouse gas fluxes

Soils harbour diverse soil fauna and a wide range of soil microorganisms. These fauna and microorganisms directly contribute to soil greenhouse gas (GHG) fluxes via their respiratory and metabolic activities and indirectly by changing the physical, chemical and biological properties of soils through bioturbation, fragmentation and redistribution of plant residues, defecation, soil aggregate formation, herbivory, and grazing on microorganisms and fungi. Based on recent results, the methods and results found in relation to fauna as well as from fungi and plants are presented. The approaches are outlined, and the significance of these hitherto ignored fluxes is discussed

Stiffness in total knee arthroplasty

Stiffness is a relatively uncommon complication after total knee arthroplasty. It has been defined as a painful limitation in the range of movement (ROM). Its pathogenesis is still unclear even if some risk factors have been identified. Patient-related conditions may be difficult to treat. Preoperative ROM is the most important risk factor, but an association with diabetes, reflex sympathetic dystrophy, and general pathologies such as juvenile rheumatoid arthritis and ankylosing spondylitis has been demonstrated. Moreover, previous surgery may be an additional cause of an ROM limitation. Postoperative factors include infections, arthrofibrosis, heterotrophic ossifications, and incorrect rehabilitation protocol. Infections represent a challenging problem for the orthopaedic surgeon, and treatment may require long periods of antibiotics administration. However, it is widely accepted that an aggressive rehabilitation protocol is mandatory for a proper ROM recovery and to avoid the onset of arthrofibrosis and heterotrophic ossifications. Finally, surgery-related factors represent the most common cause of stiffness; they include errors in soft-tissue balancing, component malpositioning, and incorrect component sizing. Although closed manipulation, arthroscopic and open arthrolysis have been proposed, they may lead to unpredictable results and incomplete ROM recovery. Revision surgery must be proposed in the case of well-documented surgical errors. These operations are technically demanding and may be associated with high risk of complications; therefore they should be accurately planned and properly performed

Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments

Background Surface waters of aquatic environments have been shown to both evolve and consume hydrogen and the ocean is estimated to be the principal natural source. In some marine habitats, H2 evolution and uptake are clearly due to biological activity, while contributions of abiotic sources must be considered in others. Until now the only known biological process involved in H2 metabolism in marine environments is nitrogen fixation. Principal Findings We analyzed marine and freshwater environments for the presence and distribution of genes of all known hydrogenases, the enzymes involved in biological hydrogen turnover. The total genomes and the available marine metagenome datasets were searched for hydrogenase sequences. Furthermore, we isolated DNA from samples from the North Atlantic, Mediterranean Sea, North Sea, Baltic Sea, and two fresh water lakes and amplified and sequenced part of the gene encoding the bidirectional NAD(P)-linked hydrogenase. In 21% of all marine heterotrophic bacterial genomes from surface waters, one or several hydrogenase genes were found, with the membrane-bound H2 uptake hydrogenase being the most widespread. A clear bias of hydrogenases to environments with terrestrial influence was found. This is exemplified by the cyanobacterial bidirectional NAD(P)-linked hydrogenase that was found in freshwater and coastal areas but not in the open ocean. Significance This study shows that hydrogenases are surprisingly abundant in marine environments. Due to its ecological distribution the primary function of the bidirectional NAD(P)-linked hydrogenase seems to be fermentative hydrogen evolution. Moreover, our data suggests that marine surface waters could be an interesting source of oxygen-resistant uptake hydrogenases. The respective genes occur in coastal as well as open ocean habitats and we presume that they are used as additional energy scavenging devices in otherwise nutrient limited environments. The membrane-bound H2-evolving hydrogenases might be useful as marker for bacteria living inside of marine snow particles