60 research outputs found
LinKS:Discovering galaxy-scale strong lenses in the Kilo-Degree Survey using Convolutional Neural Networks
We present a new sample of galaxy-scale strong gravitational lens candidates, selected from 904 deg2 of Data Release 4 of the Kilo-Degree Survey, i.e. the `Lenses in the Kilo-Degree Survey' (LinKS) sample. We apply two convolutional neural networks (ConvNets) to {Ë }88 000 colour-magnitude-selected luminous red galaxies yielding a list of 3500 strong lens candidates. This list is further downselected via human inspection. The resulting LinKS sample is composed of 1983 rank-ordered targets classified as `potential lens candidates' by at least one inspector. Of these, a high-grade subsample of 89 targets is identified with potential strong lenses by all inspectors. Additionally, we present a collection of another 200 strong lens candidates discovered serendipitously from various previous ConvNet runs. A straightforward application of our procedure to future Euclid or Large Synoptic Survey Telescope data can select a sample of Ë3000 lens candidates with less than 10 per cent expected false positives and requiring minimal human intervention
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
The fifth data release of the Kilo Degree Survey: Multi-epoch optical/NIR imaging covering wide and legacy-calibration fields
\ua9 The Authors 2024.We present the final data release of the Kilo-Degree Survey (KiDS-DR5), a public European Southern Observatory (ESO) wide-field imaging survey optimised for weak gravitational lensing studies. We combined matched-depth multi-wavelength observations from the VLT Survey Telescope and the VISTA Kilo-degree INfrared Galaxy (VIKING) survey to create a nine-band optical-to-near-infrared survey spanning 1347 deg2. The median r-band 5Ïlimiting magnitude is 24.8 with median seeing 0.7âł. The main survey footprint includes 4 deg2 of overlap with existing deep spectroscopic surveys. We complemented these data in DR5 with a targeted campaign to secure an additional 23 deg2 of KiDS- and VIKING-like imaging over a range of additional deep spectroscopic survey fields. From these fields, we extracted a catalogue of 126 085 sources with both spectroscopic and photometric redshift information, which enables the robust calibration of photometric redshifts across the full survey footprint. In comparison to previous releases, DR5 represents a 34% areal extension and includes an i-band re-observation of the full footprint, thereby increasing the effective i-band depth by 0.4 magnitudes and enabling multi-epoch science. Our processed nine-band imaging, single- and multi-band catalogues with masks, and homogenised photometry and photometric redshifts can be accessed through the ESO Archive Science Portal
Development and recent progress on ammonia synthesis catalysts for HaberâBosch process
Due to its essential use as a fertilizer, ammonia synthesis from nitrogen and hydrogen is considered to be one of the most important chemical processes of the last 100âyears. Since then, an enormous amount of work has been undertaken to investigate and develop effective catalysts for this process. Although the catalytic synthesis of ammonia has been extensively studied in the last century, many new catalysts are still currently being developed to reduce the operating temperature and pressure of the process and to improve the conversion of reactants to ammonia. New catalysts for the HaberâBosch process are the key to achieving green ammonia production in the foreseeable future. Herein, the history of ammonia synthesis catalyst development is briefly described as well as recent progress in catalyst development with the aim of building an overview of the current state of ammonia synthesis catalysts for the HaberâBosch process. The new emerging ammonia synthesis catalysts, including electride, hydride, amide, perovskite oxide hydride/oxynitride hydride, nitride, and oxide promoted metals such as Fe, Co, and Ni, are promising alternatives to the conventional fusedâFe and promotedâRu catalysts for existing ammonia synthesis plants and future distributed green ammonia synthesis based on the HaberâBosch process
Consistent lensing and clustering in a low-S8 Universe with BOSS, DES Year 3, HSC Year 1, and KiDS-1000
We evaluate the consistency between lensing and clustering based on measurements from BOSS combined with galaxy-galaxy lensing from DES-Y3, HSC-Y1, KiDS-1000. We find good agreement between these lensing datasets. We model the observations using the Dark Emulator and fit the data at two fixed cosmologies: Planck (S 8 = 0.83), and a Lensing cosmology (S 8 = 0.76). For a joint analysis limited to large scales, we find that both cosmologies provide an acceptable fit to the data. Full utilisation of the higher signal-to-noise small-scale measurements is hindered by uncertainty in the impact of baryon feedback and assembly bias, which we account for with a reasoned theoretical error budget. We incorporate a systematic inconsistency parameter for each redshift bin, A, that decouples the lensing and clustering. With a wide range of scales, we find different results for the consistency between the two cosmologies. Limiting the analysis to the bins for which the impact of the lens sample selection is expected to be minimal, for the Lensing cosmology, the measurements are consistent with A=1; A = 0.91 ± 0.04 (A = 0.97 ± 0.06) using DES+KiDS (HSC). For the Planck case, we find a discrepancy: A = 0.79 ± 0.03 (A = 0.84 ± 0.05) using DES+KiDS (HSC). We demonstrate that a kSZ-based estimate for baryonic effects alleviates some of the discrepancy in the Planck cosmology. This analysis demonstrates the statistical power of small-scale measurements, but caution is still warranted given modelling uncertainties and foreground sample selection effects
KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing
We present cosmological parameter constraints from a tomographic weak gravitational lensing analysis of âŒ450 deg2 of imaging data from the Kilo Degree Survey (KiDS). For a flat Î cold dark matter (ÎCDM) cosmology with a prior on H0 that encompasses the most recent direct measurements, we find S8âĄÏ8Ωm/0.3âââââââ=0.745±0.039â . 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 2.3Ï tension in S8 and âsubstantial discordanceâ 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 âself-calibratingâ 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
Consistent lensing and clustering in a low-S8 Universe with BOSS, DES Year 3, HSC Year 1, and KiDS-1000
We evaluate the consistency between lensing and clustering based on measurements from Baryon Oscillation Spectroscopic Survey combined with galaxy-galaxy lensing from Dark Energy Survey (DES) Year 3, Hyper Suprime-Cam Subaru Strategic Program (HSC) Year 1, and Kilo-Degree Survey (KiDS)-1000. We find good agreement between these lensing data sets. We model the observations using the DARK EMULATOR and fit the data at two fixed cosmologies: Planck (S8 = 0.83), and a Lensing cosmology (S8 = 0.76). For a joint analysis limited to large scales, we find that both cosmologies provide an acceptable fit to the data. Full utilization of the higher signal-to-noise small-scale measurements is hindered by uncertainty in the impact of baryon feedback and assembly bias, which we account for with a reasoned theoretical error budget. We incorporate a systematic inconsistency parameter for each redshift bin, A, that decouples the lensing and clustering. With a wide range of scales, we find different results for the consistency between the two cosmologies. Limiting the analysis to the bins for which the impact of the lens sample selection is expected to be minimal, for the Lensing cosmology, the measurements are consistent with A = 1; A = 0.91 ± 0.04 (A = 0.97 ± 0.06) using DES+KiDS (HSC). For the Planck case, we find a discrepancy: A = 0.79 ± 0.03 (A = 0.84 ± 0.05) using DES+KiDS (HSC). We demonstrate that a kinematic Sunyaev-Zeldovich-based estimate for baryonic effects alleviates some of the discrepancy in the Planck cosmology. This analysis demonstrates the statistical power of small-scale measurements; however, caution is still warranted given modelling uncertainties and foreground sample selection effects
DES Y3 + KiDS-1000: Consistent cosmology combining cosmic shear surveys
We present a joint cosmic shear analysis of the Dark Energy Survey (DES Y3)
and the Kilo-Degree Survey (KiDS-1000) in a collaborative effort between the
two survey teams. We find consistent cosmological parameter constraints between
DES Y3 and KiDS-1000 which, when combined in a joint-survey analysis, constrain
the parameter with a mean value of
. The mean marginal is lower than the maximum a
posteriori estimate, , owing to skewness in the marginal
distribution and projection effects in the multi-dimensional parameter space.
Our results are consistent with constraints from observations of the
cosmic microwave background by Planck, with agreement at the level.
We use a Hybrid analysis pipeline, defined from a mock survey study quantifying
the impact of the different analysis choices originally adopted by each survey
team. We review intrinsic alignment models, baryon feedback mitigation
strategies, priors, samplers and models of the non-linear matter power
spectrum.Comment: 38 pages, 21 figures, 15 tables, submitted to the Open Journal of
Astrophysics. Watch the core team discuss this analysis at
https://cosmologytalks.com/2023/05/26/des-kid
KiDS and Euclid: Cosmological implications of a pseudo angular power spectrum analysis of KiDS-1000 cosmic shear tomography
Large scale structure and cosmolog
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