Extremely Large Telescope

Abstract:

We conduct a search for strong gravitational lenses in the Dark Energy Survey (DES) Year 6 imaging data. We implement a pre-trained Vision Transformer (ViT) for our machine learning (ML) architecture and adopt interactive machine learning to construct a training sample with multiple classes to address common types of false positives. Our ML model reduces ∼236 million DES cutout images to 22,564 targets of interest, including ∼85% of previously reported galaxy–galaxy lens candidates discovered in DES. These targets were visually inspected by citizen scientists, who ruled out ∼90% as false positives. Of the remaining 2618 candidates, 149 were expert-classified as “definite” lenses and 516 as “probable” lenses, for a total of 665 systems, with 147 of these candidates being newly identified. Additionally, we trained a second ViT to find double-source plane lens systems, finding at least one double-source system. Our main ViT excels at identifying galaxy–galaxy lenses, consistently assigning high scores to candidates with high expert assessments. The top 800 ViT-scored images include ∼100 of our “definite” lens candidates. This selection is an order of magnitude higher in purity than previous convolutional neural-network-based lens searches and demonstrates the feasibility of applying our methodology for discovering large samples of lenses in future surveys.

Abstract:

We present a detailed study of the inner regions of NGC 7582, a nearby Seyfert 2 galaxy, from the Galaxy Activity, Torus, and Outflow Survey (GATOS). The galaxy hosts a circumnuclear star-forming disc and an active galactic nucleus (AGN)-driven biconical ionized outflow. Using James Webb Space Telescope Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument/Medium-Resolution Spectrometer (MIRI/MRS) integral-field spectroscopy, we analyse ionic emission lines spanning a wide range of ionization potentials (IPs, –126 eV). Gaussian line-profile fitting reveals kinematic stratification: low-IP species ( eV; e.g. [Fe ii], [Ar ii], and [Ne ii]) trace ordered disc rotation with PA , while high-IP species ( eV; e.g. [O iv], [Mg iv], and [Ne v]) follow the outflow with PA . Outflowing gas exhibits systematically higher velocity dispersions ( km s−1) than the disc ( km s−1), consistent with turbulent or bulk motions. Intermediate-IP lines, [S iii], [Ar iii], and [Ne iii], show contributions from both components, with the outflow characterized by higher dispersion, lower amplitude, and higher velocities in double-Gaussian fits. For these lines, a thin inclined disc plus 1D outflow model enables robust separation and quantification of the disc and outflow velocity fields. The outflow is consistent with a hollow bicone capable of accelerating gas beyond the local escape velocity, implying most material is unlikely to be re-accreted. The ionization cone opening angle shows no dependence on IP, indicating the AGN torus polar regions are largely unobscured. Our study provides new insights into AGN-driven outflows and circumnuclear disc dynamics, offering a framework to disentangle overlapping interstellar medium kinematics in nearby active galaxies.

Abstract:

We present the architecture, implementation, and on-sky validation of the fully automated acquisition and guiding system (AG) developed for the WEAVE instrument on the William Herschel Telescope. The AG operates in two distinct modes, corresponding to the observing modes of WEAVE. For the large integral field unit, an off-axis imaging guider is used, for which we have devised an automatic acquisition method based on pattern recognition of stellar asterisms matched against Gaia predictions. For the multi-object spectrograph and the mini-integral field units, a multifibre guider uses up to eight coherent image guide fibre bundles to derive and apply continuous corrections in azimuth, altitude, and rotation. The system performs complete astrometric calculations, including atmospheric differential refraction and instrument flexure, for each guide frame, enabling accurate target placement and stable closed-loop guiding in all configurations. To support development, commissioning, and operational validation, we have also built a high-fidelity simulation mode that reproduces the behaviour of the telescope control system and of the AG cameras, and we release the standalone camera simulator as open-source software. Using two years of routine WEAVE operations spanning commissioning and early survey phases, we present a statistically robust characterization of AG performance, demonstrating that both modes meet design requirements and are ready for sustained survey operations.