187 research outputs found
Optimization of spectroscopic surveys for testing non-Gaussianity
We investigate optimization strategies to measure primordial non-Gaussianity
with future spectroscopic surveys. We forecast measurements coming from the 3D
galaxy power spectrum and compute constraints on primordial non-Gaussianity
parameters f_NL and n_NG. After studying the dependence on those parameters
upon survey specifications such as redshift range, area, number density, we
assume a reference mock survey and investigate the trade-off between number
density and area surveyed. We then define the observational requirements to
reach the detection of f_NL of order 1. Our results show that while power
spectrum constraints on non-Gaussianity from future spectroscopic surveys can
be competitive with current CMB limits, measurements from higher-order
statistics will be needed to reach a sub unity precision in the measurements of
the non-Gaussianity parameter f_NL.Comment: 12 pages, 10 figure
Self-Similar Solutions of Triaxial Dark Matter Halos
We investigate the collapse and internal structure of dark matter halos. We
consider halo formation from initially scale-free perturbations, for which
gravitational collapse is self-similar. Fillmore and Goldreich (1984) and
Bertschinger (1985) solved the one dimensional (i.e. spherically symmetric)
case. We generalize their results by formulating the three dimensional
self-similar equations. We solve the equations numerically and analyze the
similarity solutions in detail, focusing on the internal density profiles of
the collapsed halos. By decomposing the total density into subprofiles of
particles that collapse coevally, we identify two effects as the main
determinants of the internal density structure of halos: adiabatic contraction
and the shape of a subprofile shortly after collapse; the latter largely
reflects the triaxiality of the subprofile. We develop a simple model that
describes the results of our 3D simulations. In a companion paper, we apply
this model to more realistic cosmological fluctuations, and thereby explain the
origin of the nearly universal (NFW-like) density profiles found in N-body
simulations.Comment: corresponds to version published in Ap
Some assembly required: assembly bias in massive dark matter halos
We study halo assembly bias for cluster-sized halos. Previous work has found
little evidence for correlations between large-scale bias and halo mass
assembly history for simulated cluster-sized halos, in contrast to the
significant correlation found between bias and concentration for halos of this
mass. This difference in behavior is surprising, given that both concentration
and assembly history are closely related to the same properties of the
linear-density peaks that collapse to form halos. Using publicly available
simulations, we show that significant assembly bias is indeed found in the most
massive halos with , using essentially any definition of
halo age. For lower halo masses , no correlation is found
between bias and the commonly used age indicator , the half-mass time.
We show that this is a mere accident, and that significant assembly bias exists
for other definitions of halo age, including those based on the time when the
halo progenitor acquires some fraction of the ultimate mass at . For
halos with , the sense of assembly bias changes
sign at . We explore the origin of this behavior, and argue that it
arises because standard definitions of halo mass in halo finders do not
correspond to the collapsed, virialized mass that appears in the spherical
collapse model used to predict large-scale clustering. Because bias depends
strongly on halo mass, these errors in mass definition can masquerade as or
even obscure the assembly bias that is physically present. More physically
motivated halo definitions using splashback should be free of this particular
defect of standard halo finders.Comment: 7 pages, 4 figures, to be submitted to JCA
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