75 research outputs found
Constraint of Void Bias on Primordial non-Gaussianity
We study the large-scale bias parameter of cosmic voids with primordial
non-Gaussian (PNG) initial conditions of the local type. In this scenario, the
dark matter halo bias exhibits a characteristic scale dependence on large
scales, which has been recognized as one of the most promising probes of the
local PNG. Using a suite of -body simulations with Gaussian and non-Gaussian
initial conditions, we find that the void bias features scale-dependent
corrections on large scales, similar to its halo counterpart. We find excellent
agreement between the numerical measurement of the PNG void bias and the
general peak-background split prediction. Contrary to halos, large voids
anti-correlate with the dark matter density field, and the large-scale Gaussian
void bias ranges from positive to negative values depending on void size and
redshift. Thus, the information in the clustering of voids can be complementary
to that of the halos. Using the Fisher matrix formalism for multiple tracers,
we demonstrate that including the scale-dependent bias information from voids,
constraints on the PNG parameter can be tightened by a factor of
two compared to the accessible information from halos alone, when the sampling
density of tracers reaches .Comment: 7 pages, 4 figures; dn/dlnsigma_8 prediction implemented and
excellent agreement with simulation results obtained. Matched to published
versio
Large-Scale Clustering of Cosmic Voids
We study the clustering of voids using -body simulations and simple
theoretical models. The excursion-set formalism describes fairly well the
abundance of voids identified with the watershed algorithm, although the void
formation threshold required is quite different from the spherical collapse
value. The void cross bias is measured and its large-scale value
is found to be consistent with the peak background split results. A simple
fitting formula for is found. We model the void auto-power
spectrum taking into account the void biasing and exclusion effect. A good fit
to the simulation data is obtained for voids with radii 30 Mpc/,
especially when the void biasing model is extended to 1-loop order. However,
the best-fit bias parameters do not agree well with the peak-background split
results. Being able to fit the void auto-power spectrum is particularly
important not only because it is the direct observable in galaxy surveys, but
also our method enables us to treat the bias parameters as nuisance parameters,
which are sensitive to the techniques used to identify voids.Comment: 20 pages, 14 figures, minor changes to match published versio
Measuring nonlocal Lagrangian peak bias
We investigate nonlocal Lagrangian bias contributions involving gradients of
the linear density field, for which we have predictions from the excursion set
peak formalism. We begin by writing down a bias expansion which includes all
the bias terms, including the nonlocal ones. Having checked that the model
furnishes a reasonable fit to the halo mass function, we develop a 1-point
cross-correlation technique to measure bias factors associated with
2-distributed quantities. We validate the method with numerical realizations of
peaks of Gaussian random fields before we apply it to N-body simulations. We
focus on the lowest (quadratic) order nonlocal contributions. We can reproduce
our measurement of \chi_{10} if we allow for an offset between the Lagrangian
halo center-of-mass and the peak position. The sign and magnitude of \chi_{10}
is consistent with Lagrangian haloes sitting near linear density maxima. The
resulting contribution to the halo bias can safely be ignored for M = 10^13
Msun/h, but could become relevant at larger halo masses. For the second
nonlocal bias \chi_{01} however, we measure a much larger magnitude than
predicted by our model. We speculate that some of this discrepancy might
originate from nonlocal Lagrangian contributions induced by nonspherical
collapse.Comment: (v2): presentation clarified. agreement with the simulation improved.
accepted for publication. 11 pages, 8 figure
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