The Correlation Function of Clusters of Galaxies and the Amplitude of Mass Fluctuations in the Universe

We show that if a sample of galaxy clusters is complete above some mass threshold, then hierarchical clustering theories for structure formation predict its autocorrelation function to be determined purely by the cluster abundance and by the spectrum of linear density fluctuations. Thus if the shape of the initial fluctuation spectrum is known, its amplitude $\sigma_8$ can be estimated directly from the correlation length of a cluster sample in a way which is independent of the value of $\Omega_0$. If the cluster mass corresponding to the sample threshold is also known, it provides an independent estimate of the quantity $\sigma_8\Omega_0^{0.6}$. Thus cluster data should allow both $\sigma_8$ and $\Omega_0$ to be determined observationally. We explore these questions using N-body simulations together with a simple but accurate analytical model based on extensions of Press-Schechter theory. Applying our results to currently available data we find that if the linear fluctuation spectrum has a shape similar to that suggested by the APM galaxy survey, then a correlation length $r_0$ in excess of 20\mpch for Abell clusters would require $\sigma_8>1$, while r_0<15\mpch would require $\sigma_8<0.5$. With conventional estimates of the relevant mass threshold these imply \Omega_0\la 0.3 and \Omega_0\ga 1 respectively.Comment: Latex, 25 pages (including 8 PS figures). The PS-file of the paper is also available via anonymous ftp at: ftp://ibm-3.mpa-garching.mpg.de/pub/jing/xicc.ps . Submitted to MNRAS. In the replaced version, a typo in Eq.(1a) is fixe

Contamination of Tributyltin on Selected Marine Invertebrates Collected from Selected Fishery Harbors in Sri Lanka

Tributyltin (TBT) included in the organotin group is considered some of the most toxic chemicals introduced into aquatic environments by anthropogenic activities. Because of it broad range of biocidal activities, they are used for different agricultural and industrial purposes. However, TBT deleterious effects on aquatic biota are well reported and included endocrine distruption, immunotoxicity, neurotoxicity, genotoxicity and metabolic dysfunction. Aquatic invertebrates are key members of zooplankton and have vital roles in food chains. Therefore, the endocrine- disrupting effects of TBT on invertebrates can be transferred to other organisms including human being. This study aims to find the contamination status of TBT in invertebrate samples collected from selected fishery harbors where boat activities are high. Perna viridis, P. perna, Crassostrea madrasensis and Thais sp. in nearly same size were collected from Galle, Kirinda, Mirissa and Trincomalee fishery harbors where the highest water dissolved TBT concentrations were recorded in preliminary screening. Composite sample of each species (10 g) were subjected to TBT extraction using Solid Phase Micro Extraction (SPME) fiber and Potassium Borohydride was used as a deriving agent of TBT chloride into TBT hydride. Quantifications were done in Gas Chromatography Mass Spectrometry (GC-MS) using HP5 column and followed the splitless mode. The results showed that the highest TBT concentration was recorded in P. viridis (53±1.7 ngL-1) following P. perna, C. madrasensis and Thais sp. were 41±2.5 ngL-1, 43±2.4 ngL-1 and 28±1.4 ngL-1 respectively. The concentrations of TBT in these marine invertebrate samples exceeded the concentration which cause severe adverse effects (1 ngL-1). Hence, fishes and marine mammals can be contaminated by ingesting TBT contaminated invertebrates. Therefore, the consumption of contaminated seafood could be risks to human health.Keywords: Tributyltin (TBT), Marine invertebrates, Imposex, Solid Phase Micro Extraction (SPME), Gas Chromatography Mass Spectrometry (GC-MS

Qualitative Determination, Quantitative Evaluation and Comparative Insecticidal Potential of Ruta Graveolens Essential Oil and Its Major Constituents in the Management of Two Stored Pests Sitophilus Zeamais (Coleoptera: Curculionidae) And Corcyra Cephalon

Eco-chemical control based on essential oil mediated plant-insect interactions is an alternative method to the unsystematic use of insecticides, due to advanced structural diversity and allelopathic potential of essential oils. In this sense, present work was aimed at qualitative and quantitative investigation of chemical composition and the evaluation of insecticidal activities of Ruta graveolens essential oil and its major constituents against Sitophilus zeamais and Corcyra cephalonica in stored maize. Fresh leaves were subjected to hydrodistillaton and the chemical composition of oil was studied. Essential oil and its major constituents were then assessed for their allelopathic activity on test insects. Fifty components were identified, where long chain aliphatic 2-methyl ketones predominated the oil as major constituents. Results revealed strong concentration-, insect species- and time-dependent toxicities, in which oil caused 100 % mortalities at concentrations of 1.52 and 0.46 µL/cm2 against S. zeamais and C. cephalonica respectively after 24 hours of exposure. In aliphatic 2-methyl ketone series, respective congeners having odd and even number of carbon atoms were more effective on S. zeamais and C. cephalonica. These findings provide a scientific basis for the eco-potential of using essential oil of R. graveolens and its major constituents in integrated insect pest management programs

Effect of Total Phosphorous, pH and Electric Conductivity on the Seasonal Occurrence of Geosmin in Some Water Bodies Sri Lanka

Cyanobacteria and actinomycetes are well known for their capability to produce taste and odour (T and O) causing compounds in water as their secondary metabolites. Geosmin (trans-1, 10-dimethyl-trans-9-decalol)) is one of the major T and O causing compounds producing earthy T and O and has become a major issue in worldwide water sector. Despite of not detecting as a human health hazard, presence of this odorant directly causes drinking water aesthetically unacceptable and leads to consumer rejection of treated drinking water due to conventional treatment processes do not remove Geosmin. Geosmin is prevailing in some Sri Lankan raw water bodies where water is taken for treatment purposes by National Water Supply and Drainage Board. The objective of the present study was to find the seasonal variation of Geosmin in Sri Lankan water bodies with respect to some physico-chemical aspects aiming to manage the T and O issue in Sri Lanka. Sampling was carried out from June 2016 to June 2018 covering both dry and wet seasons. Geosmin contamination level in 20 water bodies in Sri Lanka were analysed by Solid Phase Micro Extraction (SPME) coupled with Gas Chromatography Mass Spectrometry (GC/MS). The physico-chemical parameters of the water body were measured using standard spectrometric and titrimetric methods. Quantification and enumeration of phytoplankton were carried out with standard method using Acidified Lugol’s solution at final concentration of 1% following natural sedimentation. Geosmin concentration of the analysed samples varied between 7.8±3.27 to 34.6±1.32 ng/L throughout the dry season and from 0 to 18.3±1.22 ng/L during the wet season. Among the selected raw water bodies; the highest level of Geosmin was recorded in Sagama tank (34.6±1.32 ng/L) while the lowest was detected in Nallachchiya tank (7.8±3.27) during the dry season. During the wet season, the highest level of Geosmin was recorded in Sagama tank (18.3±1.22 ng/L) where not detected levels were recorded in Kondawatuwana tank, Jayanthi tank, Kanthale tank and Unnichchi tanks. Anabaena sp., Microcystis sp., Cylindrospermopsis sp., Oscillatoria sp., Cyclotella sp. Volvox sp., Gloeocystis sp., and Uroglenopsis sp. are the major taste and odour forming cyanobacteria recorded from the reservoirs during the study. Total cyanobacteria cell density varied between 102,560±2.28 cells/ml (Thuruwila tank) to 3,649±0.34 cells/ml (Ridiyagama tank) in dry season whereas from 98,235±4.73 (Beire lake) cells/ml to 135±3.11 cells/ml (Kanthale tank) during wet season. Detected Geosmin level in dry season was greater than the wet season. The Pearson’s correlation coefficient analysis revealed a significantly strong positive correlation between Geosmin level and the total phosphorus concentration (r=0.850, (p&lt;0.05), water pH (r=0.788 (p&lt;0.05)) and the Electrical Conductivity level (r=0.612, (p&lt;0.05). Further, it was found that cyanobacteria cell density (r=0.691, (p&lt;0.05)) had a significant positive correlation with Geosmin level in water bodies. These findings are crucial in understanding and managing natural reservoirs to eliminate T and O issue to provide a better quality drinking water to Sri Lankan general public.Keywords: Geosmin, SPME, GC/MS, Physico-chemical parameters, Seasonal variatio

Satellites and haloes of dwarf galaxies

We study the abundance of satellite galaxies as a function of primary stellar mass using the Sloan Digital Sky Survey/Data Release 7 (SDSS/DR7) spectroscopic catalogue. In contrast with previous studies, which focused mainly on bright primaries, our central galaxies span a wide range of stellar mass, 107.5 ⩽ Mpri*/M⊙ ⩽ 1011, from dwarfs to central cluster galaxies. Our analysis confirms that the average number of satellites around bright primaries, when expressed in terms of satellite-to-primary stellar mass ratio (msat*/M*pri), is a strong function of Mpri*. On the other hand, satellite abundance is largely independent of primary mass for dwarf primaries (Mpri* < 1010 M⊙). These results are consistent with galaxy formation models in the Λ cold dark matter (ΛCDM) scenario. We find excellent agreement between SDSS data and semianalytic mock galaxy catalogues constructed from the Millennium-II Simulation. Satellite galaxies trace dark matter substructure in ΛCDM, so satellite abundance reflects the dependence on halo mass, M200, of both substructure and galaxy stellar mass (M*). Since dark matter substructure is almost scale free, the dependence of satellite abundance on primary mass results solely from the well-defined characteristic mass in the galaxy mass-halo mass relation. On dwarf galaxy scales, where models predict a power-law scaling, M*∝M2.5200, similarity is preserved and satellite abundance is independent of primary mass. For primaries brighter than the characteristic mass of the M*–M200 relation, satellite abundance increases strongly with primary mass. Our results provide strong support for the steep, approximately power-law dependence of dwarf galaxy mass on halo mass envisioned in ΛCDM galaxy formation models

Toxicity evaluation and volatile component analysis of tropical marine sponge Clathria sp. (Schmidt, 1862)

Marine sponge Clathria sp. holds a significant position in marine natural product research due to its wide range of secondary metabolites. Extensive distribution of genus Clathria in the world causes variances in chemical profile in relation to their environment. The purpose of this study was to evaluate toxicity and profile secondary metabolites of sponge Clathria sp. collected from coastal waters off Mannar, Sri Lanka. Methanolic crude extract of the sponge was subjected to preliminary phytochemical screening and GC-MS analysis. Alkaloids, steroids, terpenoids, and saponins were subjected to phytochemical screening. Seven steroidal derivatives; Cholesta-3,5-diene, stigmastan-3,5-diene, cholesta-7,14-diene, (5. alpha.), ergosta-4,6,22-triene, cholesta-2,4-diene and cholest-2-ene were identified through GC-MS analysis. Brine shrimp lethality assay was carried out to test the toxicity of the extract. LC50 value estimated at 624 ppm. Results of the present study suggest that ethanolic extract of marine sponge Clathria sp. contains steroidal derivatives and certain toxicity, which will be important in future studies to understand the antifouling property of Clathria sp.KEYWORDS: Clathria sp., phytochemical, GC-MS, secondary metabolites, cytotoxicit

Early structure in Lambda CDM

We use a novel technique to simulate the growth of one of the most massive progenitors of a supercluster region from redshift z 80, when its mass was about 10 M, until the present day. Our nested sequence of N-body resimulations allows us to study in detail the structure both of the dark matter object itself and of its environment. Our effective resolution is optimal at redshifts of 49, 29, 12, 5 and 0 when the dominant object has mass 1.2 × 105, 5 × 107, 2 × 1010, 3 × 1012 and 8 × 1014 h1 M, respectively, and contains 106 simulation particles within its virial radius. Extended Press–Schechter (EPS) theory correctly predicts both this rapid growth and the substantial overabundance of massive haloes we find at early times in regions surrounding the dominant object. Although the large-scale structure in these regions differs dramatically from a scaled version of its present-day counterpart, the internal structure of the dominant object is remarkably similar. Molecular hydrogen cooling could start as early as z 49 in this object, while cooling by atomic hydrogen becomes effective at z 39. If the first stars formed in haloes with virial temperature 2000 K, their comoving abundance at z= 49 should be similar to that of dwarf galaxies today, while their comoving correlation length should be 2.5 h1 Mpc

Outskirts of Nearby Disk Galaxies: Star Formation and Stellar Populations

The properties and star formation processes in the far-outer disks of nearby spiral and dwarf irregular galaxies are reviewed. The origin and structure of the generally exponential profiles in stellar disks is considered to result from cosmological infall combined with a non-linear star formation law and a history of stellar migration and scattering from spirals, bars, and random collisions with interstellar clouds. In both spirals and dwarfs, the far-outer disks tend to be older, redder and thicker than the inner disks, with the overall radial profiles suggesting inside-out star formation plus stellar scattering in spirals, and outside-in star formation with a possible contribution from scattering in dwarfs. Dwarf irregulars and the far-outer parts of spirals both tend to be gas dominated, and the gas radial profile is often non-exponential although still decreasing with radius. The ratio of H-alpha to far-UV flux tends to decrease with lower surface brightness in these regions, suggesting either a change in the initial stellar mass function or the sampling of that function, or a possible loss of H-alpha photons.Comment: 20 pages, 8 figures, Invited review, Book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

Voids in the Simulated Local Universe

We use simulations of the formation and evolution of the galaxy population in the Local Universe to address the issue of whether the standard theoretical model succeeds in producing empty regions as large and as dark as the observed nearby ones. We follow the formation of galaxies in an LCDM universe and work with mock catalogues which can resolve the morphology of LMC sized galaxies, and the luminosity of objects 6 times fainter. We look for a void signature in sets of virialized haloes selected by mass, as well as in mock galaxy samples selected according to observationally relevant quantities, like luminosity, colour, or morphology. We find several void regions with diameter 10 Mpc/h in the simulation where gravity seems to have swept away even the smallest haloes we were able to track. We probe the environment density of the various populations and compute luminosity functions for galaxies residing in underdense, mean density and overdense regions. We also use nearest neighbour statistics to check possible void populations, taking $L_{*}$ spirals as reference neighbours. Down to our resolution limits, we find that all types of galaxies avoid the same regions, and that no class appears to populate the voids defined by the bright galaxies.Comment: 14 pages, 6 figures. Submitted to MNRAS. A high-resolution version of Figure 1 and galaxy populations analysed here are available at http://www.mpa-garching.mpg.de/NumCos/CR/Voids