52 research outputs found
Recovering the Tidal Field in the Projected Galaxy Distribution
We present a method to recover and study the projected gravitational tidal
forces from a galaxy survey containing little or no redshift information. The
method and the physical interpretation of the recovered tidal maps as a tracer
of the cosmic web are described in detail. We first apply the method to a
simulated galaxy survey and study the accuracy with which the cosmic web can be
recovered in the presence of different observational effects, showing that the
projected tidal field can be estimated with reasonable precision over large
regions of the sky. We then apply our method to the 2MASS survey and present a
publicly available full-sky map of the projected tidal forces in the local
Universe. As an example of an application of these data we further study the
distribution of galaxy luminosities across the different elements of the cosmic
web, finding that, while more luminous objects are found preferentially in the
most dense environments, there is no further segregation by tidal environment.Comment: 18 pages, 13 figures. Data publicly available at
http://intensitymapping.physics.ox.ac.uk/2mass_tidal.htm
A Small-Scale Modification to the Lensing Kernel
Calculations of the Cosmic Microwave Background lensing power implemented
into the standard cosmological codes such as CAMB and CLASS usually treat the
surface of last scatter as an infinitely thin screen. However, since the CMB
anisotropies are smoothed out on scales smaller than the diffusion length due
to the effect of Silk damping, the photons which carry information about the
small-scale density distribution come from slightly earlier times than the
standard recombination time. The dominant effect is the scale dependence of the
mean redshift associated with the fluctuations during recombination. We find
that fluctuations at come from a characteristic
redshift of , while fluctuations at
come from a characteristic redshift of . We then estimate the
corrections to the lensing kernel and the related power spectra due to this
effect. We conclude that neglecting it would result in a deviation from the
true value of the lensing kernel at the half percent level at small CMB scales.
For an all-sky, noise-free experiment, this corresponds to a
shift in the observed temperature power spectrum on small scales ().Comment: 5 pages, 5 figure
Full forward model of galaxy clustering statistics with simulation lightcones
Novel summary statistics beyond the standard 2-point correlation function
(2PCF) are necessary to capture the full astrophysical and cosmological
information from the small-scale (Mpc) galaxy clustering.
However, the analysis of beyond-2PCF statistics on small scales is challenging
because we lack the appropriate treatment of observational systematics for
arbitrary summary statistics of the galaxy field. In this paper, we develop a
full forward modeling pipeline for any summary statistics using high-fidelity
simulation lightcones that accounts for all observational systematics and is
appropriate for a wide range of summary statistics. We apply our forward model
approach to a fully realistic mock galaxy catalog and demonstrate that we can
recover unbiased constraints on the underlying galaxy--halo connection model
using two separate summary statistics: the standard 2PCF and the novel -th
nearest neighbor (NN) statistics, which are sensitive to correlation
functions of all orders. We expect that applying this forward model approach to
current and upcoming surveys while leveraging a multitude of summary statistics
will become a powerful technique in maximally extracting information from the
non-linear scales.Comment: comments welcom
The halo light cone catalogues of AbacusSummit
We describe a method for generating halo catalogues on the light-cone using the ABACUSSUMMIT suite of N-body simulations. The main application of these catalogues is the construction of realistic mock galaxy catalogues and weak lensing maps on the sky. Our algorithm associates the haloes from a set of coarsely spaced snapshots with their positions at the time of light-cone crossing by matching halo particles to on-the-fly light-cone particles. It then records the halo and particle information into an easily accessible product, which we call the ABACUSSUMMIT halo light-cone catalogues. Our recommended use of this product is in the halo mass regime of Mhalo > 2.1 × 1011 M⊙ h−1 for the base resolution simulations, i.e. haloes containing at least 100 particles, where the interpolated halo properties are most reliable. To test the validity of the obtained catalogues, we perform various visual inspections and consistency checks. In particular, we construct galaxy mock catalogues of emission-line galaxies (ELGs) at z ∼ 1 by adopting a modified version of the ABACUSHOD script, which builds on the standard halo occupation distribution (HOD) method by including various extensions. We find that the multipoles of the autocorrelation function are consistent with the predictions from the full-box snapshot, implicitly validating our algorithm. In addition, we compute and output CMB convergence maps and find that the auto- and cross-power spectrum agrees with the theoretical prediction at the sub-per-cent level
Hefty enhancement of cosmological constraints from the DES Y1 data using a Hybrid Effective Field Theory approach to galaxy bias
We present a re-analysis of the shear and galaxy clustering data from
first-year Dark Energy Survey data (DES Y1), making use of a Hybrid Effective
Field Theory (HEFT) approach to model the galaxy-matter relation on weakly
non-linear scales, initially proposed in Modi et al. (2020). This allows us to
explore the enhancement in cosmological constraints enabled by extending the
galaxy clustering scale range typically used in projected large-scale structure
analysis. Our analysis is based on a recomputed harmonic-space data vector and
covariance matrix, carefully accounting for all sources of mode-coupling,
non-Gaussianity and shot noise, which allows us to provide robust
goodness-of-fit measures. We use the AbacusSummit suite of simulations to build
an emulator for the HEFT model predictions. We find that this model can explain
the galaxy clustering and shear data up to wavenumbers . We constrain at the fiducial , improving to at . This
represents a and improvement on the constraints derived
respectively on both parameters using a linear bias relation on a reduced scale
range (), in spite of the 15
additional parameters involved in the HEFT model. Our constraints are
investigative and subject to certain caveats discussed in the text.Comment: 27 pages, 7 figures, 3 table
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