9,437 research outputs found
Testing the Halo Model Against the SDSS Photometric Survey
We present halo model predictions for the expected angular clustering and
associated errors from the completed Sloan Digital Sky Survey (SDSS)
photometric galaxy sample. These results are used to constrain halo model
parameters under the assumption of a fixed LCDM cosmology using standard Fisher
matrix techniques. Given the ability of the five-color SDSS photometry to
separate galaxies into sub-populations by intrinsic color, we also use
extensions of the standard halo model formalism to calculate the expected
clustering of red and blue galaxy sub-populations as a further test of the
galaxy evolution included in the semi-analytic methods for populating dark
matter halos with galaxies. The extremely small sample variance and Poisson
errors from the completed SDSS survey should result in very impressive
constraints (~1-10%) on the halo model parameters for a simple
magnitude-limited sample and should provide an extremely useful check on the
behavior of current and future N-body simulations and semi-analytic techniques.
We also show that similar constraints are possible using a narrow selection
function, as would be possible using photometric redshifts, without making
linear assumptions regarding the evolution of the underlying power spectra. In
both cases, we explore the effects of uncertainty in the selection function on
the resulting constraints and the degeneracies between various combinations of
parameters.Comment: 16 pages, 17 figure
Small-scale intraspecific life history variation in herbivorous spider mites (Tetranychus pacificus) is associated with host plant cultivar.
Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a "common garden experiment" of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment
Primordial Non-Gaussianity and the NRAO VLA Sky Survey
The NRAO VLA Sky Survey (NVSS) is the only dataset that allows an accurate
determination of the auto-correlation function (ACF) on angular scales of
several degrees for Active Galactic Nuclei (AGNs) at typical redshifts . Surprisingly, the ACF is found to be positive on such large scales
while, in the framework of the standard hierarchical clustering scenario with
Gaussian primordial perturbations it should be negative for a
redshift-independent effective halo mass of order of that found for
optically-selected quasars. We show that a small primordial non-Gaussianity can
add sufficient power on very large scales to account for the observed NVSS ACF.
The best-fit value of the parameter , quantifying the amplitude of
primordial non-Gaussianity of local type is (
error bar) and ( confidence level),
corresponding to a detection of non-Gaussianity significant at the confidence level. The minimal halo mass of NVSS sources is found to
be () strikingly
close to that found for optically selected quasars. We discuss caveats and
possible physical and systematic effects that can impact on the results.Comment: 6 pages, 5 figure
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