113 research outputs found
An Empirical Model For Intrinsic Alignments: Insights From Cosmological Simulations
We extend current models of the halo occupation distribution (HOD) to include
a flexible, empirical framework for the forward modeling of the intrinsic
alignment (IA) of galaxies. A primary goal of this work is to produce mock
galaxy catalogs for the purpose of validating existing models and methods for
the mitigation of IA in weak lensing measurements. This technique can also be
used to produce new, simulation-based predictions for IA and galaxy clustering.
Our model is probabilistically formulated, and rests upon the assumption that
the orientations of galaxies exhibit a correlation with their host dark matter
(sub)halo orientation or with their position within the halo. We examine the
necessary components and phenomenology of such a model by considering the
alignments between (sub)halos in a cosmological dark matter only simulation. We
then validate this model for a realistic galaxy population in a set of
simulations in the Illustris-TNG suite. We create an HOD mock with
Illustris-like correlations using our method, constraining the associated IA
model parameters, with the between our model's correlations
and those of Illustris matching as closely as 1.4 and 1.1 for
orientation--position and orientation--orientation correlation functions,
respectively. By modeling the misalignment between galaxies and their host
halo, we show that the 3-dimensional two-point position and orientation
correlation functions of simulated (sub)halos and galaxies can be accurately
reproduced from quasi-linear scales down to . We also find
evidence for environmental influence on IA within a halo. Our
publicly-available software provides a key component enabling efficient
determination of Bayesian posteriors on IA model parameters using observational
measurements of galaxy-orientation correlation functions in the highly
nonlinear regime.Comment: 17 pages, 12 figures, 3 tables, for submission to The Open Journal of
Astrophysics, code available at https://github.com/astropy/halotool
PSFs of coadded images
We provide a detailed exploration of the connection between choice of
coaddition schemes and the point-spread function (PSF) of the resulting coadded
images. In particular, we investigate what properties of the coaddition
algorithm lead to the final coadded image having a well-defined PSF. The key
elements of this discussion are as follows:
1. We provide an illustration of how linear coaddition schemes can produce a
coadd that lacks a well-defined PSF even for relatively simple scenarios and
choices of weight functions.
2. We provide a more formal demonstration of the fact that a linear coadd
only has a well-defined PSF in the case that either (a) each input image has
the same PSF or (b) the coadd is produced with weights that are independent of
the signal.
3. We discuss some reasons that two plausible nonlinear coaddition algorithms
(median and clipped-mean) fail to produce a consistent PSF profile for stars.
4. We demonstrate that all nonlinear coaddition procedures fail to produce a
well-defined PSF for extended objects.
In the end, we conclude that, for any purpose where a well-defined PSF is
desired, one should use a linear coaddition scheme with weights that do not
correlate with the signal and are approximately uniform across typical objects
of interest.Comment: 13 pages, 4 figures; pedagogical article for submission to the Open
Journal of Astrophysic
Impact of Point Spread Function Higher Moments Error on Weak Gravitational Lensing II: A Comprehensive Study
Weak gravitational lensing, or weak lensing, is one of the most powerful
probes for dark matter and dark energy science, although it faces increasing
challenges in controlling systematic uncertainties as \edit{the statistical
errors become smaller}. The Point Spread Function (PSF) needs to be precisely
modeled to avoid systematic error on the weak lensing measurements. The weak
lensing biases induced by errors in the PSF model second moments, i.e., its
size and shape, are well-studied. However, Zhang et al. (2021) showed that
errors in the higher moments of the PSF may also be a significant source of
systematics for upcoming weak lensing surveys. Therefore, the goal of this work
is to comprehensively investigate the modeling quality of PSF moments from the
to order, and estimate their impact on
cosmological parameter inference. We propagate the \textsc{PSFEx} higher
moments modeling error in the HSC survey dataset to the weak lensing
\edit{shear-shear correlation functions} and their cosmological analyses. We
find that the overall multiplicative shear bias associated with errors in PSF
higher moments can cause a shift on the cosmological
parameters for LSST Y10. PSF higher moment errors also cause additive biases in
the weak lensing shear, which, if not accounted for in the cosmological
parameter analysis, can induce cosmological parameter biases comparable to
their uncertainties for LSST Y10. We compare the \textsc{PSFEx} model
with PSF in Full FOV (\textsc{Piff}), and find similar performance in modeling
the PSF higher moments. We conclude that PSF higher moment errors of the future
PSF models should be reduced from those in current methods to avoid a need to
explicitly model these effects in the weak lensing analysis.Comment: 24 pages, 17 figures, 3 tables; Submitted to MNRAS; Comments welcome
Cosmological parameter constraints from galaxy–galaxy lensing and galaxy clustering with the SDSS DR7
Recent studies have shown that the cross-correlation coefficient between galaxies and dark matter is very close to unity on scales outside a few virial radii of galaxy haloes, independent of the details of how galaxies populate dark matter haloes. This finding makes it possible to determine the dark matter clustering from measurements of galaxy–galaxy weak lensing and galaxy clustering. We present new cosmological parameter constraints based on large-scale measurements of spectroscopic galaxy samples from the Sloan Digital Sky Survey (SDSS) data release 7. We generalize the approach of Baldauf et al. to remove small-scale information (below 2 and 4 h^(−1) Mpc for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 deg^2, containing 69 150, 62 150 and 35 088 galaxies with mean redshifts of 0.11, 0.28 and 0.40. We clearly detect scale-dependent galaxy bias for the more luminous galaxy samples, at a level consistent with theoretical expectations. When we vary both σ_8 and Ω_m (and marginalize over non-linear galaxy bias) in a flat Λ cold dark matter model, the best-constrained quantity is σ_8(Ω_m/0.25)^(0.57) = 0.80 ± 0.05 (1σ, stat. + sys.), where statistical and systematic errors (photometric redshift and shear calibration) have comparable contributions, and we have fixed n_s = 0.96 and h = 0.7. These strong constraints on the matter clustering suggest that this method is competitive with cosmic shear in current data, while having very complementary and in some ways less serious systematics. We therefore expect that this method will play a prominent role in future weak lensing surveys. When we combine these data with Wilkinson Microwave Anisotropy Probe 7-year (WMAP7) cosmic microwave background (CMB) data, constraints on σ_8, Ω_m, H_0, w_(de) and ∑m_ν become 30–80 per cent tighter than with CMB data alone, since our data break several parameter degeneracies
King's Framework and Theory in Japan, Sweden, and the United States
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71420/1/j.1547-5069.1995.tb00835.x.pd
Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor
revisio
A Joint Roman Space Telescope and Rubin Observatory Synthetic Wide-Field Imaging Survey
We present and validate 20 deg of overlapping synthetic imaging surveys
representing the full depth of the Nancy Grace Roman Space Telescope
High-Latitude Imaging Survey (HLIS) and five years of observations of the Vera
C. Rubin Observatory Legacy Survey of Space and Time (LSST). The two synthetic
surveys are summarized, with reference to the existing 300 deg of LSST
simulated imaging produced as part of Dark Energy Science Collaboration (DESC)
Data Challenge 2 (DC2). Both synthetic surveys observe the same simulated DESC
DC2 universe. For the synthetic Roman survey, we simulate for the first time
fully chromatic images along with the detailed physics of the Sensor Chip
Assemblies derived from lab measurements using the flight detectors. The
simulated imaging and resulting pixel-level measurements of photometric
properties of objects span a wavelength range of 0.3 to 2.0 m. We
also describe updates to the Roman simulation pipeline, changes in how
astrophysical objects are simulated relative to the original DC2 simulations,
and the resulting simulated Roman data products. We use these simulations to
explore the relative fraction of unrecognized blends in LSST images, finding
that 20-30% of objects identified in LSST images with -band magnitudes
brighter than 25 can be identified as multiple objects in Roman images. These
simulations provide a unique testing ground for the development and validation
of joint pixel-level analysis techniques of ground- and space-based imaging
data sets in the second half of the 2020s -- in particular the case of joint
Roman--LSST analyses
CFHTLenS: a Gaussian likelihood is a sufficient approximation for a cosmological analysis of third-order cosmic shear statistics
We study the correlations of the shear signal between triplets of sources in the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) to probe cosmological parameters via the matter bispectrum. In contrast to previous studies, we adopt a non-Gaussian model of the data likelihood which is supported by our simulations of the survey. We find that for state-of-the-art surveys, similar to CFHTLenS, a Gaussian likelihood analysis is a reasonable approximation, albeit small differences in the parameter constraints are already visible. For future surveys we expect that a Gaussian model becomes inaccurate. Our algorithm for a refined non-Gaussian analysis and data compression is then of great utility especially because it is not much more elaborate if simulated data are available. Applying this algorithm to the third-order correlations of shear alone in a blind analysis, we find a good agreement with the standard cosmological model: Σ8=σ8(Ωm/0.27)0.64=0.79+0.08−0.11 for a flat Λ cold dark matter cosmology with h = 0.7 ± 0.04 (68 per cent credible interval). Nevertheless our models provide only moderately good fits as indicated by χ2/dof = 2.9, including a 20 per cent rms uncertainty in the predicted signal amplitude. The models cannot explain a signal drop on scales around 15 arcmin, which may be caused by systematics. It is unclear whether the discrepancy can be fully explained by residual point spread function systematics of which we find evidence at least on scales of a few arcmin. Therefore we need a better understanding of higher order correlations of cosmic shear and their systematics to confidently apply them as cosmological probes
The LSST Dark Energy Science Collaboration (DESC) Science Requirements Document
The Large Synoptic Survey Telescope (LSST) Dark Energy Science Collaboration
(DESC) will use five cosmological probes: galaxy clusters, large scale
structure, supernovae, strong lensing, and weak lensing. This Science
Requirements Document (SRD) quantifies the expected dark energy constraining
power of these probes individually and together, with conservative assumptions
about analysis methodology and follow-up observational resources based on our
current understanding and the expected evolution within the field in the coming
years. We then define requirements on analysis pipelines that will enable us to
achieve our goal of carrying out a dark energy analysis consistent with the
Dark Energy Task Force definition of a Stage IV dark energy experiment. This is
achieved through a forecasting process that incorporates the flowdown to
detailed requirements on multiple sources of systematic uncertainty. Future
versions of this document will include evolution in our software capabilities
and analysis plans along with updates to the LSST survey strategy.Comment: 32 pages + 60 pages of appendices. This is v1 of the DESC SRD, an
internal collaboration document that is being made public and is not planned
for submission to a journal. Data products for reproducing key plots are
available at the LSST DESC Zenodo community,
https://zenodo.org/communities/lsst-desc; see "Executive Summary and User
Guide" for instructions on how to use and cite those product
Shaking off the neoliberal shackles:“Democratic Emergence” and the negotiation of democratic knowledge in the Middle East North Africa context
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