113 research outputs found
Encircling the dark: constraining dark energy via cosmic density in spheres
The recently published analytic probability density function for the mildly
non-linear cosmic density field within spherical cells is used to build a
simple but accurate maximum likelihood estimate for the redshift evolution of
the variance of the density, which, as expected, is shown to have smaller
relative error than the sample variance. This estimator provides a competitive
probe for the equation of state of dark energy, reaching a few percent accuracy
on wp and wa for a Euclid-like survey. The corresponding likelihood function
can take into account the configuration of the cells via their relative
separations. A code to compute one-cell density probability density functions
for arbitrary initial power spectrum, top-hat smoothing and various spherical
collapse dynamics is made available online so as to provide straightforward
means of testing the effect of alternative dark energy models and initial
power-spectra on the low-redshift matter distribution.Comment: 7 pages, replaced to match the MNRAS accepted versio
Intrinsic alignment of simulated galaxies in the cosmic web: implications for weak lensing surveys
The intrinsic alignment of galaxy shapes (by means of their angular momentum) and their cross-correlation with the surrounding dark matter tidal field are investigated using the 160000, z=1.2 synthetic galaxies extracted from the high-resolution cosmological hydrodynamical simulation horizon-agn. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and colour. For the low-mass galaxies, this spin is locally aligned with the tidal field ‘filamentary' direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of our synthetic catalogue are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to∼10h− 1 Mpc comoving distance. We also report a correlation of the projected ellipticities of blue, intermediate-mass galaxies on a similar scale at a level of 10−4 which could be a concern for cosmic shear measurements. We do not report any measurable intrinsic alignments of the reddest galaxies of our sample. This work is a first step towards the use of very realistic catalogue of synthetic galaxies to evaluate the contamination of weak lensing measurement by the intrinsic galactic alignment
Optimization of early growth stage treatments of the vine: experimentations on the artificial vine EvaSprayViti
Cylinders out of a top hat: Counts-in-cells for projected densities
© 2017 The Authors. Large deviation statistics is implemented to predict the statistics of cosmic densities in cylinders applicable to photometric surveys. It yields few per cent accurate analytical predictions for the one-point probability distribution function (PDF) of densities in concentric or compensated cylinders; and also captures the density dependence of their angular clustering (cylinder bias). All predictions are found to be in excellent agreement with the cosmological simulation Horizon Run 4 in the quasi-linear regime where standard perturbation theory normally breaks down. These results are combined with a simple local bias model that relates dark matter and tracer densities in cylinders and validated on simulated halo catalogues. This formalism can be used to probe cosmology with existing and upcoming photometric surveys like DES, Euclid or WFIRST containing billions of galaxies
Bailing Out the Milky Way: Variation in the Properties of Massive Dwarfs Among Galaxy-Sized Systems
Recent kinematical constraints on the internal densities of the Milky Way's
dwarf satellites have revealed a discrepancy with the subhalo populations of
simulated Galaxy-scale halos in the standard CDM model of hierarchical
structure formation. This has been dubbed the "too big to fail" problem, with
reference to the improbability of large and invisible companions existing in
the Galactic environment. In this paper, we argue that both the Milky Way
observations and simulated subhalos are consistent with the predictions of the
standard model for structure formation. Specifically, we show that there is
significant variation in the properties of subhalos among distinct host halos
of fixed mass and suggest that this can reasonably account for the deficit of
dense satellites in the Milky Way. We exploit well-tested analytic techniques
to predict the properties in a large sample of distinct host halos with a
variety of masses spanning the range expected of the Galactic halo. The
analytic model produces subhalo populations consistent with both Via Lactea II
and Aquarius, and our results suggest that natural variation in subhalo
properties suffices to explain the discrepancy between Milky Way satellite
kinematics and these numerical simulations. At least ~10% of Milky Way-sized
halos host subhalo populations for which there is no "too big to fail" problem,
even when the host halo mass is as large as M_host = 10^12.2 h^-1 M_sun.
Follow-up studies consisting of high-resolution simulations of a large number
of Milky Way-sized hosts are necessary to confirm our predictions. In the
absence of such efforts, the "too big to fail" problem does not appear to be a
significant challenge to the standard model of hierarchical formation.
[abridged]Comment: 12 pages, 3 figures; accepted by JCAP. Replaced with published
versio
Euclid preparation. XXVIII. Forecasts for ten different higher-order weak lensing statistics
Recent cosmic shear studies have shown that higher-order statistics (HOS) developed by independent teams now outperform standard two-point estimators in terms of statistical precision thanks to their sensitivity to the non-Gaussian features of large-scale structure. The aim of the Higher-Order Weak Lensing Statistics (HOWLS) project is to assess, compare, and combine the constraining power of ten different HOS on a common set of Euclid-like mocks, derived from N-body simulations. In this first paper of the HOWLS series, we computed the nontomographic (Ω, σ) Fisher information for the one-point probability distribution function, peak counts, Minkowski functionals, Betti numbers, persistent homology Betti numbers and heatmap, and scattering transform coefficients, and we compare them to the shear and convergence two-point correlation functions in the absence of any systematic bias. We also include forecasts for three implementations of higher-order moments, but these cannot be robustly interpreted as the Gaussian likelihood assumption breaks down for these statistics. Taken individually, we find that each HOS outperforms the two-point statistics by a factor of around two in the precision of the forecasts with some variations across statistics and cosmological parameters. When combining all the HOS, this increases to a 4.5 times improvement, highlighting the immense potential of HOS for cosmic shear cosmological analyses with Euclid. The data used in this analysis are publicly released with the paper
Dancing in the dark: galactic properties trace spin swings along the cosmic web
A large-scale hydrodynamical cosmological simulation, Horizon-AGN, is used to investigate the alignment between the spin of galaxies and the cosmic filaments above redshift 1.2. The analysis of more than 150000 galaxies per time step in the redshift range 1.2 < z < 1.8 with morphological diversity shows that the spin of low-mass blue galaxies is preferentially aligned with their neighbouring filaments, while high-mass red galaxies tend to have a perpendicular spin. The reorientation of the spin of massive galaxies is provided by galaxy mergers, which are significant in their mass build-up. We find that the stellar mass transition from alignment to misalignment happens around 3 × 1010 M⊙. Galaxies form in the vorticity-rich neighbourhood of filaments, and migrate towards the nodes of the cosmic web as they convert their orbital angular momentum into spin. The signature of this process can be traced to the properties of galaxies, as measured relative to the cosmic web. We argue that a strong source of feedback such as active galactic nuclei is mandatory to quench in situ star formation in massive galaxies and promote various morphologies. It allows mergers to play their key role by reducing post-merger gas inflows and, therefore, keeping spins misaligned with cosmic filament
Angular momentum and galaxy formation revisited
Motivated by new kinematic data in the outer parts of early-type galaxies
(ETGs), we re-examine angular momentum (AM) in all galaxy types. We present
methods for estimating the specific AM j, focusing on ETGs, to derive relations
between stellar j_* and mass M_* (after Fall 1983). We perform analyses of 8
galaxies out to ~10 R_e, finding that data at 2 R_e are sufficient to estimate
total j_*. Our results contravene suggestions that ellipticals (Es) harbor
large reservoirs of hidden j_* from AM transport in major mergers. We carry out
a j_*-M_* analysis of literature data for ~100 nearby bright galaxies of all
types. The Es and spirals form parallel j_*-M_* tracks, which for spirals is
like the Tully-Fisher relation, but for Es derives from a mass-size-rotation
conspiracy. The Es contain ~3-4 times less AM than equal-mass spirals. We
decompose the spirals into disks+bulges and find similar j_*-M_* trends to
spirals and Es overall. The S0s are intermediate, and we propose that
morphological types reflect disk/bulge subcomponents following separate j_*-M_*
scaling relations -- providing a physical motivation for characterizing
galaxies by mass and bulge/disk ratio. Next, we construct idealized
cosmological models of AM content, using a priori estimates of dark matter halo
spin and mass. We find that the scatter in halo spin cannot explain the
spiral/E j_* differences, but the data are matched if the galaxies retained
different fractions of initial j (~60% and ~10%). We consider physical
mechanisms for j_* and M_* evolution (outflows, stripping, collapse bias,
merging), emphasizing that the vector sum of such processes must produce the
observed j_*-M_* relations. A combination of early collapse and multiple
mergers (major/minor) may account for the trend for Es. More generally, the
observed AM variations represent fundamental constraints for any galaxy
formation model.Comment: ApJS, in press, 61 pages, 34 figures, abstract abridge
Euclid Preparation. XXVIII. Forecasts for ten different higher-order weak lensing statistics
Recent cosmic shear studies have shown that higher-order statistics (HOS) developed by independent teams now outperform standard two-point estimators in terms of statistical precision thanks to their sensitivity to the non-Gaussian features of large-scale structure. The aim of the Higher-Order Weak Lensing Statistics (HOWLS) project is to assess, compare, and combine the constraining power of ten different HOS on a common set of -like mocks, derived from N-body simulations. In this first paper of the HOWLS series, we computed the nontomographic (, ) Fisher information for the one-point probability distribution function, peak counts, Minkowski functionals, Betti numbers, persistent homology Betti numbers and heatmap, and scattering transform coefficients, and we compare them to the shear and convergence two-point correlation functions in the absence of any systematic bias. We also include forecasts for three implementations of higher-order moments, but these cannot be robustly interpreted as the Gaussian likelihood assumption breaks down for these statistics. Taken individually, we find that each HOS outperforms the two-point statistics by a factor of around two in the precision of the forecasts with some variations across statistics and cosmological parameters. When combining all the HOS, this increases to a times improvement, highlighting the immense potential of HOS for cosmic shear cosmological analyses with . The data used in this analysis are publicly released with the paper
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