ORCID Profile
0000-0001-9419-3947
Current Organisation
Allen Institute
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Publisher: Oxford University Press (OUP)
Date: 23-11-2017
Publisher: Oxford University Press (OUP)
Date: 09-02-2017
DOI: 10.1093/MNRAS/STX342
Publisher: EDP Sciences
Date: 12-2017
DOI: 10.1051/0004-6361/201731267
Abstract: Context. Measuring and calibrating relations between cluster observables is critical for resource-limited studies. The mass–richness relation of clusters offers an observationally inexpensive way of estimating masses. Its calibration is essential for cluster and cosmological studies, especially for high-redshift clusters. Weak gravitational lensing magnification is a promising and complementary method to shear studies, that can be applied at higher redshifts. Aims. We aim to employ the weak lensing magnification method to calibrate the mass–richness relation up to a redshift of 1.4. We used the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) galaxy cluster candidates (0.2 z 1.4) and optical data from the Canada France Hawaii Telescope (CFHT) to test whether magnification can be effectively used to constrain the mass of high-redshift clusters. Methods. Lyman-break galaxies (LBGs) selected using the u -band dropout technique and their colours were used as a background s le of sources. LBG positions were cross-correlated with the centres of the s le of SpARCS clusters to estimate the magnification signal, which was optimally-weighted using an externally-calibrated LBG luminosity function. The signal was measured for cluster sub-s les, binned in both redshift and richness. Results. We measured the cross-correlation between the positions of galaxy cluster candidates and LBGs and detected a weak lensing magnification signal for all bins at a detection significance of 2.6–5.5 σ . In particular, the significance of the measurement for clusters with z 1.0 is 4.1 σ for the entire cluster s le we obtained an average M 200 of 1.28 -0.21 +0.23 × 10 14 M ⊙ . Conclusions. Our measurements demonstrated the feasibility of using weak lensing magnification as a viable tool for determining the average halo masses for s les of high redshift galaxy clusters. The results also established the success of using galaxy over-densities to select massive clusters at z 1. Additional studies are necessary for further modelling of the various systematic effects we discussed.
Publisher: Oxford University Press (OUP)
Date: 05-04-2018
DOI: 10.1093/MNRAS/STY859
Publisher: EDP Sciences
Date: 10-2020
DOI: 10.1051/0004-6361/202038835
Abstract: 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 s le with unknown redshifts and a reference s le with known redshifts. It represents an attractive alternative to colour-based methods of redshift calibration. Here 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 s le and the overlapping spectroscopic reference s les. 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 s les at high redshifts. Clustering mean redshifts are unbiased at |Δ z | 0.006 under these conditions. The redshift evolution of the galaxy bias of the reference and target s les represents one of the most important systematic errors when estimating clustering redshifts. It 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 |Δ z |∼0.04. 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.
Publisher: EDP Sciences
Date: 2020
DOI: 10.1051/0004-6361/201834878
Abstract: We present a tomographic cosmic shear analysis of the Kilo-Degree Survey (KiDS) combined with the VISTA Kilo-Degree Infrared Galaxy Survey. This is the first time that a full optical to near-infrared data set has been used for a wide-field cosmological weak lensing experiment. This unprecedented data, spanning 450 deg 2 , allows us to significantly improve the estimation of photometric redshifts, such that we are able to include robustly higher-redshift sources for the lensing measurement, and – most importantly – to solidify our knowledge of the redshift distributions of the sources. Based on a flat ΛCDM model we find S 8 ≡ σ 8 Ω m /0.3 = 0.737 +0.040 −0.036 in a blind analysis from cosmic shear alone. The tension between KiDS cosmic shear and the Planck-Legacy CMB measurements remains in this systematically more robust analysis, with S 8 differing by 2.3 σ . This result is insensitive to changes in the priors on nuisance parameters for intrinsic alignment, baryon feedback, and neutrino mass. KiDS shear measurements are calibrated with a new, more realistic set of image simulations and no significant B-modes are detected in the survey, indicating that systematic errors are under control. When calibrating our redshift distributions by assuming the 30-band COSMOS-2015 photometric redshifts are correct (following the Dark Energy Survey and the Hyper Suprime-Cam Survey), we find the tension with Planck is alleviated. The robust determination of source redshift distributions remains one of the most challenging aspects for future cosmic shear surveys.
Publisher: Oxford University Press (OUP)
Date: 02-11-2016
Location: Germany
No related grants have been discovered for Christopher B. Morrison.