66 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
Improving small-scale CMB lensing reconstruction
Over the past decade, the gravitational lensing of the Cosmic Microwave
Background (CMB) has become a powerful tool for probing the matter distribution
in the Universe. The standard technique used to reconstruct the CMB lensing
signal employs the quadratic estimator (QE) method, which has recently been
shown to be suboptimal for lensing measurements on very small scales in
temperature and polarization data. We implement a simple, more optimal method
for the small-scale regime, which involves taking the direct inverse of the
background gradient. We derive new techniques to make continuous maps of
lensing using this "Gradient-Inversion" (GI) method and validate our method
with simulated data, finding good agreement with predictions. For idealized
simulations of lensing cross- and autospectra that neglect foregrounds, we
demonstrate that our method performs significantly better than previous
quadratic estimator methods in temperature; at , it reduces errors
on the lensing auto-power spectrum by a factor of for both idealized
CMB-S4 and Simons Observatory-like experiments and by a factor of
for cross-correlations of CMB-S4-like lensing reconstruction and the true
lensing field. We caution that the level of the neglected small-scale
foreground power, while low in polarization, is very high in temperature;
though we briefly outline foreground mitigation methods, further work on this
topic is required. Nevertheless, our results show the future potential for
improved small-scale CMB lensing measurements, which could provide stronger
constraints on cosmological parameters and astrophysics at high redshifts
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
CDM or self-interacting neutrinos? - how CMB data can tell the two models apart
Of the many proposed extensions to the CDM paradigm, a model in
which neutrinos self-interact until close to the epoch of matter-radiation
equality has been shown to provide a good fit to current cosmic microwave
background (CMB) data, while at the same time alleviating tensions with
late-time measurements of the expansion rate and matter fluctuation amplitude.
Interestingly, CMB fits to this model either pick out a specific large value of
the neutrino interaction strength, or are consistent with the extremely weak
neutrino interaction found in CDM, resulting in a bimodal posterior
distribution for the neutrino self-interaction cross section. In this paper, we
explore why current cosmological data select this particular large neutrino
self-interaction strength, and by consequence, disfavor intermediate values of
the self-interaction cross section. We show how it is the
CMB temperature anisotropies, most recently measured by the Planck satellite,
that produce this bimodality. We also establish that smaller scale temperature
data, and improved polarization data measuring the temperature-polarization
cross-correlation, will best constrain the neutrino self-interaction strength.
We forecast that the upcoming Simons Observatory should be capable of
distinguishing between the models.Comment: 7 pages, 7 figures, comments welcome, references added, version
submitted to PR
Velocity reconstruction in the era of DESI and Rubin (part II): Realistic samples on the light cone
Reconstructing the galaxy peculiar velocity field from the distribution of
large-scale structure plays an important role in cosmology. On one hand, it
gives us an insight into structure formation and gravity; on the other, it
allows us to selectively extract the kinetic Sunyaev-Zeldovich (kSZ) effect
from cosmic microwave background (CMB) maps. In this work, we employ
high-accuracy synthetic galaxy catalogs on the light cone to investigate how
well we can recover the velocity field when utilizing the three-dimensional
spatial distribution of the galaxies in a modern large-scale structure
experiment such as the Dark Energy Spectroscopic Instrument (DESI) and Rubin
Observatory (LSST). In particular, we adopt the standard technique used in
baryon acoustic oscillation (BAO) analysis for reconstructing the Zeldovich
displacements of galaxies through the continuity equation, which yields a
first-order approximation to their large-scale velocities. We investigate
variations in the number density, bias, mask, area, redshift noise, and survey
depth, and smoothing. Since our main goal is to provide guidance for planned
kSZ analysis between DESI and the Atacama Cosmology Telescope (ACT), we apply
velocity reconstruction to a faithful representation of DESI spectroscopic and
photometric targets. We report the cross-correlation coefficient between the
reconstructed and the true velocities along the line of sight. For the DESI Y1
spectroscopic survey, we expect the correlation coefficient to be , while for a photometric survey with , as is
approximately the case for the Legacy Survey used in the target selection of
DESI galaxies, shrinks by half to . We hope the results in
this paper can be used to inform future kSZ stacking studies. All scripts used
in this paper can be found here:
\url{https://github.com/boryanah/abacus_kSZ_recon}.Comment: 16 pages, 11 figures, to be submitted to PR
Analytic marginalization of uncertainties in tomographic galaxy surveys
We present a new method to marginalize over uncertainties in redshift
distributions, , within tomographic cosmological analyses applicable to
current and upcoming photometric galaxy surveys. We allow for arbitrary
deviations from the best-guess governed by a general covariance matrix
describing the uncertainty in our knowledge of redshift distributions. In
principle, this is marginalization over hundreds or thousands of new parameters
describing potential deviations as a function of redshift and tomographic bin.
However, by linearly expanding the theory predictions around a fiducial model,
this marginalization can be performed analytically, resulting in a modified
data covariance matrix that effectively downweights the modes of the data
vector that are more sensitive to redshift distribution variations. We showcase
this method by applying it to the galaxy clustering measurements from the Hyper
Suprime-Cam first data release. We illustrate how to marginalize over
sample-variance of the calibration sample and a large general systematic
uncertainty in photometric estimation methods, and explore the impact of priors
imposing smoothness in the redshift distributions.Comment: 26 pages, 7 figure
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