ORCID Profile
0000-0002-4074-0308
Current Organisations
University College London
,
Universiteit Utrecht
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Publisher: EDP Sciences
Date: 04-2021
DOI: 10.1051/0004-6361/202040136
Abstract: We present a new method for the mitigation of observational systematic effects in angular galaxy clustering through the use of corrective random galaxy catalogues. Real and synthetic galaxy data from the Kilo Degree Survey’s (KiDS) 4th Data Release (KiDS-1000) and the Full-sky Lognormal Astro-fields Simulation Kit package, respectively, are used to train self-organising maps to learn the multivariate relationships between observed galaxy number density and up to six systematic-tracer variables, including seeing, Galactic dust extinction, and Galactic stellar density. We then create ‘organised’ randoms random galaxy catalogues with spatially variable number densities, mimicking the learnt systematic density modes in the data. Using realistically biased mock data, we show that these organised randoms consistently subtract spurious density modes from the two-point angular correlation function w ( ϑ ), correcting biases of up to 12 σ in the mean clustering litude to as low as 0.1 σ , over an angular range of 7 − 100 arcmin with high signal-to-noise ratio. Their performance is also validated for angular clustering cross-correlations in a bright, flux-limited subset of KiDS-1000, comparing against an analogous s le constructed from highly complete spectroscopic redshift data. Each organised random catalogue object is a clone carrying the properties of a real galaxy, and is distributed throughout the survey footprint according to the position of the parent galaxy in systematics space. Thus, sub-s le randoms are readily derived from a single master random catalogue through the same selection as applied to the real galaxies. Our method is expected to improve in performance with increased survey area, galaxy number density, and systematic contamination, making organised randoms extremely promising for current and future clustering analyses of faint s les.
Publisher: EDP Sciences
Date: 02-2021
DOI: 10.1051/0004-6361/202039682
Abstract: We present the first measurements of the projected clustering and intrinsic alignments (IA) of galaxies observed by the Physics of the Accelerating Universe Survey (PAUS). With photometry in 40 narrow optical passbands (4500 Å–8500 Å), the quality of photometric redshift estimation is σ z ∼ 0.01(1 + z ) for galaxies in the 19 deg 2 Canada-France-Hawaii Telescope Legacy Survey W3 field, allowing us to measure the projected 3D clustering and IA for flux-limited, faint galaxies ( i 22.5) out to z ∼ 0.8. To measure two-point statistics, we developed, and tested with mock photometric redshift s les, ‘cloned’ random galaxy catalogues which can reproduce data selection functions in 3D and account for photometric redshift errors. In our fiducial colour-split analysis, we made robust null detections of IA for blue galaxies and tentative detections of radial alignments for red galaxies (∼1 − 3 σ ), over scales of 0.1 − 18 h −1 Mpc. The galaxy clustering correlation functions in the PAUS s les are comparable to their counterparts in a spectroscopic population from the Galaxy and Mass Assembly survey, modulo the impact of photometric redshift uncertainty which tends to flatten the blue galaxy correlation function, whilst steepening that of red galaxies. We investigate the sensitivity of our correlation function measurements to choices in the random catalogue creation and the galaxy pair-binning along the line of sight, in preparation for an optimised analysis over the full PAUS area.
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202140706
Abstract: We constrain the luminosity and redshift dependence of the intrinsic alignment (IA) of a nearly volume-limited s le of luminous red galaxies selected from the fourth public data release of the Kilo-Degree Survey (KiDS-1000). To measure the shapes of the galaxies, we used two complementary algorithms, finding consistent IA measurements for the overlapping galaxy s le. The global significance of IA detection across our two independent luminous red galaxy s les, with our favoured method of shape estimation, is ∼10.7 σ . We find no significant dependence with redshift of the IA signal in the range 0.2 z 0.8, nor a dependence with luminosity below L r ≲ 2.9 × 10 10 h −2 L r , ⊙ . Above this luminosity, however, we find that the IA signal increases as a power law, although our results are also compatible with linear growth within the current uncertainties. This behaviour motivates the use of a broken power law model when accounting for the luminosity dependence of IA contamination in cosmic shear studies.
Publisher: EDP Sciences
Date: 04-2019
DOI: 10.1051/0004-6361/201834714
Abstract: We directly constrain the non-linear alignment (NLA) model of intrinsic galaxy alignments, analysing the most representative and complete flux-limited s le of spectroscopic galaxies available for cosmic shear surveys. We measure the projected galaxy position-intrinsic shear correlations and the projected galaxy clustering signal using high-resolution imaging from the Kilo Degree Survey (KiDS) overlapping with the GAMA spectroscopic survey, and data from the Sloan Digital Sky Survey. Separating s les by colour, we make no significant detection of blue galaxy alignments, constraining the blue galaxy NLA litude A IA B = 0.21 −0.36 +0.37 to be consistent with zero. We make robust detections (∼9 σ ) for red galaxies, with A IA R = 3.18 −0.46 +0.47 , corresponding to a net radial alignment with the galaxy density field, and we find no evidence for any scaling of alignments with galaxy luminosity. We provide informative priors for current and future weak lensing surveys, an improvement over de facto wide priors that allow for unrealistic levels of intrinsic alignment contamination. For a colour-split cosmic shear analysis of the final KiDS survey area, we forecast that our priors will improve the constraining power on S 8 and the dark energy equation of state w 0 , by up to 62% and 51%, respectively. Our results indicate, however, that the modelling of red/blue-split galaxy alignments may be insufficient to describe s les with variable central/satellite galaxy fractions.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Harry Johnston.