88,642 research outputs found
The Aemulus Project III: Emulation of the Galaxy Correlation Function
Using the N-body simulations of the AEMULUS Project, we construct an emulator
for the non-linear clustering of galaxies in real and redshift space. We
construct our model of galaxy bias using the halo occupation framework,
accounting for possible velocity bias. The model includes 15 parameters,
including both cosmological and galaxy bias parameters. We demonstrate that our
emulator achieves ~ 1% precision at the scales of interest, 0.1<r<10 h^{-1}
Mpc, and recovers the true cosmology when tested against independent
simulations. Our primary parameters of interest are related to the growth rate
of structure, f, and its degenerate combination fsigma_8. Using this emulator,
we show that the constraining power on these parameters monotonically increases
as smaller scales are included in the analysis, all the way down to 0.1 h^{-1}
Mpc. For a BOSS-like survey, the constraints on fsigma_8 from r<30 h^{-1} Mpc
scales alone are more than a factor of two tighter than those from the fiducial
BOSS analysis of redshift-space clustering using perturbation theory at larger
scales. The combination of real- and redshift-space clustering allows us to
break the degeneracy between f and sigma_8, yielding a 9% constraint on f alone
for a BOSS-like analysis. The current AEMULUS simulations limit this model to
surveys of massive galaxies. Future simulations will allow this framework to be
extended to all galaxy target types, including emission-line galaxies.Comment: 14 pages, 8 figures, 1 table; submitted to ApJ; the project webpage
is available at https://aemulusproject.github.io ; typo in Figure 7 and
caption updated, results unchange
Simulating the Universe with MICE: The abundance of massive clusters
We introduce a new set of large N-body runs, the MICE simulations, that
provide a unique combination of very large cosmological volumes with good mass
resolution. They follow the gravitational evolution of ~ 8.5 billion particles
(2048^3) in volumes covering up to 450 (Gpc/h)^3. Our main goal is to
accurately model and calibrate basic cosmological probes that will be used by
upcoming astronomical surveys. Here we take advantage of the very large volumes
of MICE to make a robust sampling of the high-mass tail of the halo mass
function (MF). We discuss and avoid possible systematic effects in our study,
and do a detailed analysis of different error estimators. We find that
available fits to the local abundance of halos (Warren et al. (2006)) match
well the abundance in MICE up to M ~ 10^{14}\Msun, but significantly deviate
for larger masses, underestimating the mass function by 10% (30%) at M = 3.16 x
10^{14}\Msun (10^{15}\Msun). Similarly, the widely used Sheth & Tormen (1999)
fit, if extrapolated to high redshift assuming universality, leads to an
underestimation of the cluster abundance by 30%, 20% and 15% at z=0, 0.5, 1 for
M ~ [7 - 2.5 - 0.8] x 10^{14}\Msun respectively ().
We provide a re-calibration of the halo MF valid over 5 orders of magnitude in
mass, 10^{10} < M/(\Msun) < 10^{15}, that accurately describes its redshift
evolution up to z=1. We explore the impact of this re-calibration on the
determination of dark-energy, and conclude that using available fits may
systematically bias the estimate of w by as much as 50% for medium-depth (z <=
1) surveys. MICE halo catalogues are publicly available at
http://www.ice.cat/miceComment: 16 pages, 11 figures. Data publicly available at
http://www.ice.cat/mice. New version adds discussion on halo definition (SO
vs FoF) and minor modifications. Accepted for publication in MNRA
The persistent cosmic web and its filamentary structure II: Illustrations
The recently introduced discrete persistent structure extractor (DisPerSE,
Soubie 2010, paper I) is implemented on realistic 3D cosmological simulations
and observed redshift catalogues (SDSS); it is found that DisPerSE traces
equally well the observed filaments, walls, and voids in both cases. In either
setting, filaments are shown to connect onto halos, outskirt walls, which
circumvent voids. Indeed this algorithm operates directly on the particles
without assuming anything about the distribution, and yields a natural
(topologically motivated) self-consistent criterion for selecting the
significance level of the identified structures. It is shown that this
extraction is possible even for very sparsely sampled point processes, as a
function of the persistence ratio. Hence astrophysicists should be in a
position to trace and measure precisely the filaments, walls and voids from
such samples and assess the confidence of the post-processed sets as a function
of this threshold, which can be expressed relative to the expected amplitude of
shot noise. In a cosmic framework, this criterion is comparable to friend of
friend for the identifications of peaks, while it also identifies the connected
filaments and walls, and quantitatively recovers the full set of topological
invariants (Betti numbers) {\sl directly from the particles} as a function of
the persistence threshold. This criterion is found to be sufficient even if one
particle out of two is noise, when the persistence ratio is set to 3-sigma or
more. The algorithm is also implemented on the SDSS catalogue and used to locat
interesting configurations of the filamentary structure. In this context we
carried the identification of an ``optically faint'' cluster at the
intersection of filaments through the recent observation of its X-ray
counterpart by SUZAKU. The corresponding filament catalogue will be made
available online.Comment: A higher resolution version is available at
http://www.iap.fr/users/sousbie together with complementary material (movie
and data). Submitted to MNRA
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