244 research outputs found
Testing KiDS cross-correlation redshifts with simulations
Measuring cosmic shear in wide-field imaging surveys requires accurate
knowledge of the redshift distribution of all sources. The clustering-redshift
technique exploits the angular cross-correlation of a target galaxy sample with
unknown redshifts and a reference sample with known redshifts, and is an
attractive alternative to colour-based methods of redshift calibration. We test
the performance of such clustering redshift measurements using mock catalogues
that resemble the Kilo-Degree Survey (KiDS). These mocks are created from the
MICE simulation and closely mimic the properties of the KiDS source sample and
the overlapping spectroscopic reference samples. We quantify the performance of
the clustering redshifts by comparing the cross-correlation results with the
true redshift distributions in each of the five KiDS photometric redshift bins.
Such a comparison to an informative model is necessary due to the
incompleteness of the reference samples at high redshifts. Clustering mean
redshifts are unbiased at under these conditions. The
redshift evolution of the galaxy bias can be reliably mitigated at this level
of precision using auto-correlation measurements and self-consistency
relations, and will not become a dominant source of systematic error until the
arrival of Stage-IV cosmic shear surveys. Using redshift distributions from a
direct colour-based estimate instead of the true redshift distributions as a
model for comparison with the clustering redshifts increases the biases in the
mean to up to . This indicates that the interpretation of
clustering redshifts in real-world applications will require more sophisticated
(parameterised) models of the redshift distribution in the future. If such
better models are available, the clustering-redshift technique promises to be a
highly complementary alternative to other methods of redshift calibration.Comment: 21 pages, 18 figures, 10 tables, submitted to A&
KiDS-1000: cosmic shear with enhanced redshift calibration
We present a cosmic shear analysis with an improved redshift calibration for
the fourth data release of the Kilo-Degree Survey (KiDS-1000) using
self-organising maps (SOMs). Compared to the previous analysis of the KiDS-1000
data, we expand the redshift calibration sample to more than twice its size,
now consisting of data of 17 spectroscopic redshift campaigns, and
significantly extending the fraction of KiDS galaxies we are able to calibrate
with our SOM redshift methodology. We then enhance the calibration sample with
precision photometric redshifts from COSMOS2015 and the Physics of the
Accelerated Universe Survey (PAUS), allowing us to fill gaps in the
spectroscopic coverage of the KiDS data. Finally we perform a Complete
Orthogonal Sets of E/B-Integrals (COSEBIs) cosmic shear analysis of the newly
calibrated KiDS sample. We find , which is in
good agreement with previous KiDS studies and increases the tension with
measurements of the cosmic microwave background to 3.4{\sigma}. We repeat the
redshift calibration with different subsets of the full calibration sample and
obtain, in all cases, agreement within at most 0.5{\sigma} in compared to
our fiducial analysis. Including additional photometric redshifts allows us to
calibrate an additional 6 % of the source galaxy sample. Even though further
systematic testing with simulated data is necessary to quantify the impact of
redshift outliers, precision photometric redshifts can be beneficial at high
redshifts and to mitigate selection effects commonly found in spectroscopically
selected calibration samples.Comment: 18 pages, 15 figures, 6 table
A System Dynamics and Participatory Action Research Approach to Promote Healthy Living and a Healthy Weight among 10–14-Year-Old Adolescents in Amsterdam:The LIKE Programme
KiDS+VIKING-450 and DES-Y1 combined:Cosmology with cosmic shear
We present a combined tomographic weak gravitational lensing analysis of the
Kilo Degree Survey (KV450) and the Dark Energy Survey (DES-Y1). We homogenize
the analysis of these two public cosmic shear datasets by adopting consistent
priors and modeling of nonlinear scales, and determine new redshift
distributions for DES-Y1 based on deep public spectroscopic surveys. Adopting
these revised redshifts results in a reduction in the DES-inferred
value for , which decreases to a reduction when including a
systematic redshift calibration error model from mock DES data based on the
MICE2 simulation. The combined KV450 + DES-Y1 constraint on is in tension with the Planck 2018 constraint from the
cosmic microwave background at the level of . This result highlights
the importance of developing methods to provide accurate redshift calibration
for current and future weak lensing surveys.Comment: 8 pages, 4 figures, new appendix added including a simulated
analysis, version accepted for publication by A&A Letters, chains can be
found at https://github.com/sjoudaki/kidsde
OC-0056: FLAME: Influence of dose escalation to 95Gy for prostate cancer on urethra-related toxicity and QOL
KiDS-1000 catalogue::Redshift distributions and their calibration
We present redshift distribution estimates of galaxies selected from the fourth data release of the Kilo-Degree Survey over an area of ∼1000 deg2 (KiDS-1000). These redshift distributions represent one of the crucial ingredients for weak gravitational lensing measurements with the KiDS-1000 data. The primary estimate is based on deep spectroscopic reference catalogues that are re-weighted with the help of a self-organising map (SOM) to closely resemble the KiDS-1000 sources, split into five tomographic redshift bins in the photometric redshift range 0.1 < zB ≤ 1.2. Sources are selected such that they only occupy that volume of nine-dimensional magnitude-space that is also covered by the reference samples (‘gold’ selection). Residual biases in the mean redshifts determined from this calibration are estimated from mock catalogues to be ≲0.01 for all five bins with uncertainties of ∼0.01. This primary SOM estimate of the KiDS-1000 redshift distributions is complemented with an independent clustering redshift approach. After validation of the clustering-z on the same mock catalogues and a careful assessment of systematic errors, we find no significant bias of the SOM redshift distributions with respect to the clustering-z measurements. The SOM redshift distributions re-calibrated by the clustering-z represent an alternative calibration of the redshift distributions with only slightly larger uncertainties in the mean redshifts of ∼0.01 − 0.02 to be used in KiDS-1000 cosmological weak lensing analyses. As this includes the SOM uncertainty, clustering-z are shown to be fully competitive on KiDS-1000 data
The PAU Survey: a new constraint on galaxy formation models using the observed colour redshift relation
We use the GALFORM semi-analytical galaxy formation model implemented in the Planck Millennium N-body simulation to build a mock galaxy catalogue on an observer’s past lightcone. The mass resolution of this N-body simulation is almost an order of magnitude better than in previous simulations used for this purpose, allowing us to probe fainter galaxies and hence build a more complete mock catalogue at low redshifts. The high time cadence of the simulation outputs allows us to make improved calculations of galaxy properties and positions in the mock. We test the predictions of the mock against the Physics of the Accelerating Universe Survey, a narrow-band imaging survey with highly accurate and precise photometric redshifts, which probes the galaxy population over a lookback time of 8 billion years. We compare the model against the observed number counts, redshift distribution, and evolution of the observed colours and find good agreement; these statistics avoid the need for model-dependent processing of the observations. The model produces red and blue populations that have similar median colours to the observations. However, the bimodality of galaxy colours in the model is stronger than in the observations. This bimodality is reduced on including a simple model for errors in the GALFORM photometry. We examine how the model predictions for the observed galaxy colours change when perturbing key model parameters. This exercise shows that the median colours and relative abundance of red and blue galaxies provide constraints on the strength of the feedback driven by supernovae used in the model
Mass calibration of distant SPT galaxy clusters through expanded weak-lensing follow-up observations with HST, VLT, & Gemini-South
Expanding from previous work, we present weak-lensing (WL) measurements for a total sample of 30 distant (zmedian = 0.93) massive galaxy clusters from the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) Survey, measuring galaxy shapes in Hubble Space Telescope (HST) Advanced Camera for Surveys images. We remove cluster members and preferentially select z 73 1.4 background galaxies via V - I colour, employing deep photometry from VLT/FORS2 and Gemini-South/GMOS. We apply revised calibrations for the WL shape measurements and the source redshift distribution to estimate the cluster masses. In combination with earlier Magellan/Megacam results for lower-redshifts clusters, we infer refined constraints on the scaling relation between the SZ detection significance and the cluster mass, in particular regarding its redshift evolution. The mass scale inferred from the WL data is lower by a factor (at our pivot redshift z = 0.6) compared to what would be needed to reconcile a flat Planck \u3bd\u39bCDM cosmology (in which the sum of the neutrino masses is a free parameter) with the observed SPT-SZ cluster counts. In order to sensitively test the level of (dis-)agreement between SPT clusters and Planck, further expanded WL follow-up samples are needed
KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing
We present cosmological parameter constraints from a tomographic weak gravitational lensing analysis of ∼450 deg2 of imaging data from the Kilo Degree Survey (KiDS). For a flat Λ cold dark matter (ΛCDM) cosmology with a prior on H0 that encompasses the most recent direct measurements, we find S8≡σ8Ωm/0.3−−−−−−√=0.745±0.039. This result is in good agreement with other low-redshift probes of large-scale structure, including recent cosmic shear results, along with pre-Planck cosmic microwave background constraints. A 2.3σ tension in S8 and ‘substantial discordance’ in the full parameter space is found with respect to the Planck 2015 results. We use shear measurements for nearly 15 million galaxies, determined with a new improved ‘self-calibrating’ version of lensFIT validated using an extensive suite of image simulations. Four-band ugri photometric redshifts are calibrated directly with deep spectroscopic surveys. The redshift calibration is confirmed using two independent techniques based on angular cross-correlations and the properties of the photometric redshift probability distributions. Our covariance matrix is determined using an analytical approach, verified numerically with large mock galaxy catalogues. We account for uncertainties in the modelling of intrinsic galaxy alignments and the impact of baryon feedback on the shape of the non-linear matter power spectrum, in addition to the small residual uncertainties in the shear and redshift calibration. The cosmology analysis was performed blind. Our high-level data products, including shear correlation functions, covariance matrices, redshift distributions, and Monte Carlo Markov chains are available at http://kids.strw.leidenuniv.nl
KiDS-1000 Methodology:Modelling and inference for joint weak gravitational lensing and spectroscopic galaxy clustering analysis
We present the methodology for a joint cosmological analysis of weak
gravitational lensing from the fourth data release of the ESO Kilo-Degree
Survey (KiDS-1000) and galaxy clustering from the partially overlapping BOSS
and 2dFLenS surveys. Cross-correlations between galaxy positions and
ellipticities have been incorporated into the analysis, necessitating a hybrid
model of non-linear scales that blends perturbative and non-perturbative
approaches, and an assessment of contributions by astrophysical effects. All
weak lensing signals are measured consistently via Fourier-space statistics
that are insensitive to the survey mask and display low levels of mode mixing.
The calibration of photometric redshift distributions and multiplicative
gravitational shear bias has been updated, and a more complete tally of
residual calibration uncertainties is propagated into the likelihood. A
dedicated suite of more than 20000 mocks is used to assess the performance of
covariance models and to quantify the impact of survey geometry and spatial
variations of survey depth on signals and their errors. The sampling
distributions for the likelihood and the goodness-of-fit statistic
have been validated, with proposed changes to the number of degrees of freedom.
Standard weak lensing point estimates on derived from its marginal posterior are easily misinterpreted to
be biased low, and an alternative estimator and associated credible interval
have been proposed. Known systematic effects pertaining to weak lensing
modelling and inference are shown to bias by no more than 0.1 standard
deviations, with the caveat that no conclusive validation data exist for models
of intrinsic galaxy alignments. Compared to the previous KiDS analyses,
constraints are expected to improve by 20% for weak lensing alone and by 29%
for the joint analysis. [abridged]Comment: 45 pages, 34 figures, 7 tables; minor changes to match version
accepted by A&A. The KiDS-1000 data products are available for download at
http://kids.strw.leidenuniv.nl/DR4/lensing.php. This data release includes
open source software, the shear-photo-z catalogue, the cosmic shear and 3x2pt
data vectors and covariances, and posteriors in the form of Multinest chain
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