Euclid

Abstract:

We present an analysis of globular clusters (GCs) of dwarf galaxies in the Perseus galaxy cluster that explores the relationship between dwarf galaxy properties and their GCs. Our focus is on GC numbers (NGC) and GC half-number radii (RGC) around dwarf galaxies, and their relations with host galaxy stellar masses (M∗), central surface brightnesses (µ0), and effective radii (Re). This work is unique due to its large sample size and the absence of pre-selection based on µ0 and RGC for dwarf galaxies. Interestingly, we find that at a given stellar mass, RGC is almost independent of the host galaxy µ0 and Re, while RGC/Re depends on µ0 and Re. Lower surface brightness and diffuse dwarf galaxies show RGC/Re ≈ 1, while higher surface brightness and compact dwarf galaxies show RGC/Re ≈ 1.5–2. This means that for dwarf galaxies of similar stellar mass, the GCs have a similar median extent; however, their distribution is different from the field stars of their host. Additionally, low surface brightness and diffuse dwarf galaxies on average have a higher NGC than high surface brightness and compact dwarf galaxies at any given stellar mass. We also find that ultra-diffuse galaxies (UDGs) and non-UDGs in the sample have a similar RGC, while UDGs have a smaller RGC/Re (typically less than one) and a three to four times higher NGC than non-UDGs. Furthermore, when examining nucleated versus non-nucleated dwarf galaxies, we found that for M∗ > 10⁸ M, nucleated dwarf galaxies seem to have a smaller RGC and RGC/Re, with no significant differences seen between their NGC except at M∗ < 10⁸ M, where the nucleated dwarf galaxies tend to have a higher NGC. Lastly, we explored the stellar-to-halo mass ratio (SHMR) of dwarf galaxies (halo mass based on NGC) and conclude that the Perseus cluster dwarf galaxies follow the expected SHMR at z = 0 extrapolated down to M∗ = 10⁶ M .

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:

Several new galaxy-galaxy strong gravitational lenses have been detected in the early release observations (ERO) from Euclid. The all-sky survey is expected to find 170 000 new systems, which are expected to greatly enhancing studies of dark matter and dark energy, and to constrain the cosmological parameters better. As a first step, we visually inspect all galaxies in one of the ERO fields (Perseus) to identify candidate strong-lensing systems and compared them to the predictions from convolutional neural networks (CNNs). The entire ERO dataset is too large for an expert visual inspection, however. In this paper, we therefore extend the CNN analysis to the whole ERO dataset and use different CNN architectures and methods. Using five CNN architectures, we identified 8469 strong gravitational lens candidates from IE-band cutouts of 13 Euclid ERO fields and narrowed them down to 97 through visual inspection. The sample includes 14 grade A and 31 grade B candidates. We present the spectroscopic confirmation of a strong gravitational lensing candidate, EUCL J081705.61+702348.8. The foreground lensing galaxy, an early-type system at z = 0.335, and the background source, a star-forming galaxy at z = 1.475 with [O II] emission, are both identified. The lens modelling with the Euclid strong lens modelling pipeline revealed two distinct arcs in a lensing configuration, with an Einstein radius of 1.a′3;18 ± 0.3;03. This confirms the lensing nature of the system. These findings demonstrate that CNN-based candidate selection followed by visual inspection provides an effective approach for identifying strong lenses in Euclid data. They also highlight areas for improvement in future large-scale implementations.