Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

This paper describes the objectives, design, and findings of the pre-launch ground characterisation campaigns of the Euclid infrared detectors. The aim of the ground characterisations is to evaluate the performance of the detectors, to calibrate the pixel response, and to derive the pixel response correction methods. The detectors have been tested and characterised in the facilities set up for this purpose. The pixel properties, including baseline, bad pixels, quantum efficiency, inter pixel capacitance, quantum efficiency, dark current, readout noise, conversion gain, response non-linearity, and image persistence were measured and characterised for each pixel. We describe in detail the test flow definition that allows us to derive the pixel properties and we present the data acquisition and data quality check software implemented for this purpose. We also outline the measurement protocols of all the pixel properties presented and we provide a comprehensive overview of the performance of the Euclid infrared detectors as derived after tuning the operating parameters of the detectors. The main conclusion of this work is that the performance of the infrared detectors Euclid meets the requirements. Pixels classified as non-functioning accounted for less than 0.2% of all science pixels. The interpixel capacitance (IPC) coupling is minimal, the cross-talk between adjacent pixels is less than 1% between adjacent pixels, and 95% of the pixels show a quantum efficienty (QE) greater than 80% across the entire spectral range of the Euclid mission. The conversion gain is approximately 0.52 ADU/e − , with a variation of less than 1% between channels of the same detector. The reset noise is approximately equal to 23 ADU rms after reference pixel correction. The readout noise of a single frame is approximately 13 e − rms while the signal estimator noise is measured at 7 e − rms in photometric mode and 9 e − rms in spectroscopic acquisition mode. The deviation from linear response at signal levels up to 80 ke − is less than 5% for 95% of the pixels. Median persistence amplitudes are less than 0.3% of the signal, though persistence exhibits significant spatial variation and differences between detectors.

Abstract:

We forecast the constraints that the Euclid mission will place on the Hu–Sawicki f ( R ) modified gravity model using galaxy clustering and weak lensing observations. Euclid ’s primary probes will provide spectroscopic redshifts, photometric angular clustering, and weak lensing cosmic shear, thus allowing for precise tests of deviations from general relativity. We consider these observables to evaluate how well Euclid can constrain the extended model parameter f R 0 . For a fiducial value of | f R 0 | = 5 × 10 −6 , we find that in our baseline pessimistic setting, Euclid will constrain log 10 | f R 0 | at the 4% level with spectroscopic clustering, at 2.7% with the cross-correlation of photometric probes, and at 1.8% when combining all primary probes. This corresponds to an estimation on this model parameter of approximately | f R 0 = (5.0 +1.2 −0.9 × 10 −6 at the 1 σ level. We also forecast constraints for models with | f R 0 | = 5 × 10 −5 and | f R 0 | = 5 × 10 −7 , finding that Euclid will distinguish these from the standard cosmological model at more than 3 σ when using the full combination of primary probes. Euclid will be a powerful experiment to test modifications to gravity, provided that the theoretical systematics of the non-linear modelling are kept under control.

Abstract:

We present a search for z ≃ 7 Lyman-break galaxies using the 1.72 deg 2 near-infrared (NIR) UltraVISTA survey in the COSMOS field, reaching 5 σ depths in Y of 26.2. We incorporated deep Euclid optical and Euclid + Spitzer NIR imaging for a full spectral energy distribution (SED) fitting analysis. We found 289 candidate galaxies at 6.5 ≤ z ≤ 7.5 covering −22.6 ≤ M UV ≤ −20.2, faint enough to overlap with Hubble Space Telescope studies. We conducted a separate selection by including complementary Euclid performance verification imaging (reaching 5 σ depths of 26.3), yielding 140 galaxies in 0.65 deg 2 , with 38 sources unique to this sample. We computed the rest-frame UV luminosity function (UV LF) from our samples, extending below the knee ( M ∗ = 21.14 +0.28 −0.25 ). We find that the shape of the UV LF is consistent with both a Schechter function and a double power law (DPL) at the magnitudes probed by this sample, with a DPL preferred at M UV < −22.5 when bright-end results are included. The UltraVISTA + Euclid sample provides a clean measurement of the LF due to the overlapping NIR filters identifying molecular absorption features in the SEDs of ultra-cool dwarf interlopers, and additional faint galaxies were recovered. A comparison with JWST LFs at z > 7 suggests a gentle evolution in the bright-end slope, although this is limited by a lack of robust bright-end measurements at z > 9. We forecast that in the Euclid Deep Fields, the removal of contaminant ultra-cool dwarfs as point sources will be possible at J E < 24.5. Finally, we present a high-equivalent-width Lyman- α emitter candidate identified by combining HSC, VISTA, and Euclid broadband photometry, highlighting the synergistic power these instruments will have in the Euclid Auxiliary Fields for identifying extreme sources in the epoch of reionisation.

Abstract:

The Euclid large-scale weak-lensing survey aims to trace the evolution of cosmic structures up to redshift z ∼ 3 and beyond. Its success depends critically on obtaining highly accurate mean redshifts for ensembles of galaxies n ( z ) in all tomographic bins, essential for deriving robust cosmological constraints. However, photometric redshifts (photo- z s) are affected by systematic biases, arising from various sources of uncertainty and dominated by selection effects of the spectroscopic sample used for calibration. To address these challenges, we utilised self-organising maps (SOMs) with mock samples resembling the Euclid Wide Survey (EWS) from the Flagship2 simulation, to validate Euclid ’s uncertainty requirement of |Δ⟨ z ⟩| = ⟨ z est ⟩−⟨ z ⟩≤0.002(1 + z ) per tomographic bin, assuming DR3-level data. Consequently, we identify the most effective galaxy selection for our tomographic bins, while systematically examining the implementation of quality control cuts to reduce sources of uncertainty. In particular, we observe that defining the redshift tomography using the mean spectroscopic redshift (spec- z ) per SOM cell, results in none of the ten tomographic redshift bins satisfying the requirement. In contrast, the redshift tomography on the photo- z s of the EWS-like sample yields superior results, with eight out of ten bins [0 < z ≤ 2.5] meeting the Euclid requirement. To enhance the realism of our study, we morph our calibration sample to mimic the C3R2 survey in incremental steps. In this context, a maximum of six out of ten bins meet the requirement, strongly advocating the adoption of a redshift tomography defined by the photo- z s of individual galaxies rather than the commonly used mean spec- z of SOM cells. To examine the impact on the expected biases for Ω m , σ 8 , and Δ w 0 measured by Euclid , we perform a Fisher forecast for cosmic shear only, based on our redshift uncertainties. Here, we find that even under an evaluation of the uncertainty where the impact of the redshift bias is substantial, most absolute biases remain below 0.1 σ in the idealised scenario and below 0.3 σ in the more realistic case.