Lance Miller

Abstract:

This paper describes the VIS processing function (VIS PF) of the Euclid ground segment pipeline, which processes and calibrates raw data from the VIS camera. We present the algorithms used in each processing element along with a description of the on-orbit performance of VIS PF based on performance verification and Q1 datasets. We demonstrate that the principal performance metrics (image quality, astrometric accuracy, photometric calibration) are within pre-launch specifications. The image-to-image photometric scatter is less than 0.8% and absolute astrometric accuracy compared to Gaia is 5 mas. Image quality is stable over all Q1 images, with a full width at half maximum (FWHM) of 0 . ″ 16. The stacked images (combining four nominal and two short exposures) reach I E = 25.6 (10 σ , measured as the variance of 1 . ″ 3 diameter apertures). We also describe quality control metrics provided with each image, and an appendix provides a detailed description of the provided data products. The excellent quality of these images demonstrates the immense potential of Euclid VIS data for weak lensing. VIS data covering most of the extragalactic sky will provide a lasting high-resolution atlas of the Universe.

Abstract:

We present a quadratic estimator that detects and reconstructs spatially varying multiplicative (m-) bias in weak lensing shear measurements, by exploiting the mode coupling that it generates. The method combines E and B modes with inverse-variance weights, to yield an unbiased reconstruction of to first order. We study the ability of future Stage IV surveys to obtain an unbiased reconstruction of the m-bias in differing scenarios, considering differing bias morphologies, and characteristic scales, as well as differing metrics to quantify the signal-to-noise ratio of the reconstructed map. We consider an m pattern repeating on sky patches, as might be the case for an m field caused by focal-plane systematics. With a Euclid-like redshift distribution, we find that root mean square (rms) variations in m-bias may be detected at the 20 level, after stacking between and patches (rising to between and for 1 per cent rms variations, data volumes that are becoming available with upcoming surveys), depending on the morphology of the m pattern. We show that these results are robust against the cosmological model assumed in the reconstruction, as well as the presence of intrinsic alignments or baryonic effects, and that the method shows no spurious response to additive (c-) bias. These results demonstrate that percent-level, spatially varying m-bias can be detected at high significance, enabling diagnosis and mitigation in the Stage IV weak lensing era.

Abstract:

We present cosmic shear constraints from the completed Kilo-Degree Survey (KiDS), where the cosmological parameter S 8 ≡ σ 8 √Ω m /0.3 = 0.81 +0.016 −0.021 is found to be in agreement (0.73 σ ) with results from the Planck Legacy cosmic microwave background experiment. The final KiDS footprint spans 1347 square degrees of deep nine-band imaging across the optical and near-infrared (NIR), along with an extra 23-square degrees of KiDS-like calibration observations of deep spectroscopic surveys. Improvements in our redshift distribution estimation methodology, combined with our enhanced calibration data and multi-band image simulations, allowed us to extend our lensed sample out to a photometric redshift of z B ≤ 2.0. Compared to previous KiDS analyses, the increased survey area and redshift depth results in a ∼32% improvement in constraining power in terms of Σ 8 ≡ σ 8 (Ω m /0.3) α = 0.821 +0.014 −0.016 , where α = 0.58 has been optimised to match the revised degeneracy direction of σ 8 and Ω m for our current survey at higher redshift. We adopted a new physically motivated intrinsic alignment (IA) model that jointly depends on the galaxy sample’s halo mass and spectral type distributions, and which is informed by previous direct alignment measurements. We also marginalised over our uncertainty on the impact of baryon feedback on the non-linear matter power spectrum. Compared to previous KiDS analyses, we conclude that the increase seen in S 8 primarily results from our improved redshift distribution estimation and calibration, as well as a new survey area and improved image reduction. Our companion paper presents a full suite of internal and external consistency tests (including joint constraints with other datasets), finding the KiDS-Legacy dataset to be the most internally robust sample produced by KiDS to date.

Abstract:

Observations over the past decade have shown that galaxy clusters undergo the most transformative changes during the z = 1.5–2 epoch. However, challenges such as low lensing efficiency, high shape measurement uncertainty, and a scarcity of background galaxies have prevented us from characterizing their masses with weak gravitational lensing (WL) beyond redshift z ∼ 1.75. In this paper, we report the successful WL detection of JKCS 041 and XLSSC 122 at z = 1.80 and z = 1.98, respectively, utilizing deep infrared imaging data from the Hubble Space Telescope with careful removal of instrumental effects. These are the most distant clusters ever measured through WL. The mass peaks of JKCS 041 and XLSSC 122, which coincide with the X-ray peak positions of the respective clusters, are detected at the ∼3.7σ and ∼3.2σ levels, respectively. Assuming a single spherical Navarro–Frenk–White profile, we estimate that JKCS 041 has a virial mass of M200c = (5.4 ± 1.6) × 1014 M⊙, while the mass of XLSSC 122 is determined to be M200c = (3.3 ± 1.8) × 1014 M⊙. These WL masses are consistent with the estimates inferred from their X-ray observations. We conclude that although the probability of finding such massive clusters at their redshifts is certainly low, their masses can still be accommodated within the current ΛCDM paradigm.

Abstract:

This paper presents the specification, design, and development of the Visible Camera (VIS) on the European Space Agency’s Euclid mission. VIS is a large optical-band imager with a field of view of 0.54 deg2 sampled at 000 . 1 with an array of 609 Megapixels and a spatial resolution of 000 . 18. It will be used to survey approximately 14 000 deg2 of extragalactic sky to measure the distortion of galaxies in the redshift range z = 0.1–1.5 resulting from weak gravitational lensing, one of the two principal cosmology probes leveraged by Euclid. With photometric redshifts, the distribution of dark matter can be mapped in three dimensions, and the extent to which this has changed with look-back time can be used to constrain the nature of dark energy and theories of gravity. The entire VIS focal plane will be transmitted to provide the largest images of the Universe from space to date, specified to reach mAB ≥ 24.5 with a signal-to-noise ratio S/N ≥ 10 in a single broad IE ≃ (r + i + z) band over a six-year survey. The particularly challenging aspects of the instrument are the control and calibration of observational biases, which lead to stringent performance requirements and calibration regimes. With its combination of spatial resolution, calibration knowledge, depth, and area covering most of the extra-Galactic sky, VIS will also provide a legacy data set for many other fields. This paper discusses the rationale behind the conception of VIS and describes the instrument design and development, before reporting the prelaunch performance derived from ground calibrations and brief results from the in-orbit commissioning. VIS should reach fainter than mAB = 25 with S/N ≥ 10 for galaxies with a full width at half maximum of 000 . 3 in a 100 . 3 diameter aperture over the Wide Survey, and mAB ≥ 26.4 for a Deep Survey that will cover more than 50 deg2. The paper also describes how the instrument works with the Euclid telescope and survey, and with the science data processing, to extract the cosmological information.