Research Articles (Physics)

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Euclid quick data release (q1): xxv. Hunting for luminous z > 6 galaxies in the euclid deep fields – forecasts and the first bright detections
(EDP Sciences, 2026) Allen, Natalie; Oesch, Pascal A; Karagiannis, Dionysios
The evolution of the rest-frame ultraviolet luminosity function (UV LF) is a powerful probe of early star formation and galaxy stellar mass build-up. At z > 6, its bright end (MUV < −21) remains poorly constrained due to small survey volumes of existing near-infrared (NIR) space-based imaging surveys. The Euclid Deep Fields (EDFs) will cover 53 deg2 with NIR coverage down to a magnitude of 26.5 AB, providing a factor of 100 increase in area compared to previous space-based surveys. They thus offer an unprecedented opportunity to select bright z > 6 Lyman break galaxies (LBGs) and definitively constrain the bright end of the UV LF. With its NIR coverage extending to ∼2 μm, Euclid has the power to detect galaxies out to z ∼ 13. Here, we present a forecast for the number densities of z > 6 galaxies that Euclid is expected to observe in the final EDF dataset. Using synthetic photometry from spectral energy distribution (SED) templates of z = 5–15 galaxies, z = 1–4 interlopers, and Milky Way M-, L-, and T-type dwarfs, we investigate optimal selection methodologies for high-z LBGs in the EDF datasets. We find that a combination of signal-to-noise ratio (S/N) cuts with SED fitting (over optical to MIR bands) yields the highest fidelity sample, recovering more than 76% of the input synthetic z > 6 LBGs, while limiting low-z contamination to less than 10%. This contamination does not include effects from instrumental artefacts, which will impact the first Euclid data releases. Auxiliary data prove critical: optical coverage from the Hyper Suprime Camera and Vera C. Rubin Observatory will distinguish genuine Lyman breaks from contaminant features, while Spitzer Space Telescope/IRAC data are vital for recovering z > 10 sources. Based on empirical double power-law LF models, we expect more than 100 000 LBGs at z = 6–12 and more than 100 sources as far back as z > 12 in the final Euclid data release. In contrast, the steeper Schechter LF models predict no detections of z > 12 LBGs. In this work, we also present two ultra-luminous (MUV < −23.5) candidates selected from the Q1 EDF-N dataset (Euclid Quick Data Release). If their redshifts are reliable, their magnitudes suggest a DPL UV LF model at z > 9. This highlights the power of Euclid in constraining the bright end of the UV LF in the early Universe and in identifying the most luminous sources that are valuable for further follow-up observations.
Short-period pulsating hot-subdwarf stars observed by TESS in Sectors 61 – 97
(Cambridge University Press, 2026) Baran, Andrzej S; Kilkenny, David; Østensen, Roy H
We present results of a continuation of the search, started by Baran et al. (2023, 2024), for short-period pulsations in compact stellar objects observed during Sectors 61 – 97 of the TESS mission. We use newly collected and other unpublished spectroscopic data to confirm or determine spectral classification of many stars included in this work. From the TESS photometry, we identify 36 short-period hot-subdwarf pulsators, including 33 pulsators not known before the TESS mission. We present the results in a similar way to Baran et al. (2024). We provide an update on the instability strip and the evolutionary status of hot subdwarf stars with a more populated Kiel diagram. We discuss hybrid candidates as well as the results of testing correlations between theoretical predictions of the highest amplitude pulsation modes and spectroscopic parameters of stars found to be pressure-mode (p-mode) pulsators in the TESS mission. We report the discovery of the first p-mode dominated V366Aqr – type star, the first helium-enhanced hot subdwarf pulsator, and an unusual blue large-amplitude pulsator. We revise a classification of a previously reported BLAP star and correct the final TESS p-mode star statistics by accounting for a new spectral classification of two hot subdwarfs.
Euclid Quick Data Release (Q1) XVII. First Euclid statistical study of galaxy mergers and their connection to active galactic nuclei
(Astronomy and Astrophysics, 2026) Karagiannis, Dionysios; la Marca, Antonio; Wang, Lingyu
Galaxy major mergers are indicated as one of the principal pathways to trigger active galactic nuclei (AGN). We present the first statistical analysis of the major merger and AGN connection in the Euclid Deep Fields, and showcase the statistical power of the Euclid data. We constructed a stellar-mass-complete (M★ > 109.8 M⊙) sample of galaxies from the quick data release (Euclid Quick Release Q1 2025) in the redshift range z = 0.5–2. We selected AGN using X-ray detections, optical spectroscopy, and mid-infrared (MIR) colours, and by processing IE observations with an image decomposition algorithm. We used convolutional neural networks trained on cosmological hydrodynamic simulations to classify galaxies as mergers and non-mergers. We found a larger fraction of AGN in mergers compared to the non-merger controls for all AGN selections, with AGN excess factors ranging from two to six. The largest excess we observed was in the MIR AGN. Likewise, a generally larger merger fraction (fmerg) was seen in active galaxies than in the non-active controls, with the excess depending on the AGN selection method. Furthermore, we analysed fmerg as a function of the AGN bolometric luminosity (Lbol) and the contribution of the point-source component to the total galaxy light in the IE-band (fPSF) as a proxy for the relative AGN contribution fraction. We uncovered a rising fmerg, with an increasing fPSF up to fPSF ≃ 0.55, after which we observed a decreasing trend. In the range fPSF = 0.3–0.7, mergers appear to be the dominant AGN fuelling mechanism. We then derived the point-source luminosity (LPSF) and showed that fmerg monotonically increases as a function of LPSF at z < 0.9, with fmerg ≥ 50% for LPSF ≃ 2 × 1043 erg s−1. Similarly, at 0.9 ≤ z ≤ 2, fmerg rises as a function of LPSF, though mergers do not dominate until LPSF ≃ 1045 erg s−1. For the X-ray and spectroscopically detected AGN, we derived the bolometric luminosity, Lbol, which has a positive correlation with fmerg for X-ray AGN, while there is a less pronounced trend for spectroscopically selected AGN due to the smaller sample size. At Lbol > 1045 erg s−1, AGN mostly reside in mergers. We conclude that mergers are most strongly associated with the most powerful and dust-obscured AGN, which are typically linked to a fast-growing phase of the supermassive black hole, while other mechanisms, such as secular processes, might be the trigger of less luminous and dominant AGN.
Identification of the pygmy dipole resonance in a well deformed nucleus by combined isoscalar and isovector probes
(Elsevier, 2026) Pellegri, Luna; Marín-Lámbarri, Daniel José; Mukwevho, Ndinannyi justice; Rebeiro, Bernadette M.; Triambak, Smarajit
The low-energy electric dipole response in the axially deformed 154Sm nucleus was investigated for the first time using complementary probes. The isoscalar (IS) response was extracted from an ( α, α ′ γ ) coincidence experiment and the isovector (IV) response from polarization observables measured with the (p→,p→′) reaction at 0∘. Both the IS and IV responses exhibit a resonance-like structure at excitation energies 5.5-6 MeV identified as the pygmy dipole resonance. Its evolution with deformation is investigated by comparison to the spherical isotope 144Sm. The low-energy IV strength in 154Sm departs from the K -splitting picture that characterizes the IV giant dipole resonance in this nucleus. This finding is further supported by the absence of significant IS strength above 7 MeV.
The fast hi 21 cm absorption blind survey. Iii. Oh absorption search in the 21 cm absorber sample and continued hi absorption search
(American Astronomical Society, 2026) Hu, Wenkai; Wang, Yougang; Darling, Jeremy
We present the first blind search for OH 18 cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the H I 21 cm absorption search. Our previous FAST blind H I absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FAST All Sky H I Survey data (394.4 hr and 1622.1 deg2) together with FATHOMER observations, yielding four known and three new H I absorbers, for a total of 41 H I absorption systems. We search for OH absorption in 19 H I absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber toward PKS 1413+135 was redetected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between NOH and NHI, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an NOH–NHI correlation or redshift evolution of NOH/NHI. Finally, spectral stacking sets 3σ OH column density upper limits of 4.93, 1.64, and 1.72 Tex/cf,OH × 1012 cm−2 K−1 for associated, intervening, and combined samples, corresponding to [OH]/[H I] ratios of <1.66 × 10−8, <1.42 × 10−8, and <0.90 × 10−8, assuming Tex = 10 K for OH and Ts = 100 K for H I. These results place the strongest constraints to date on the OH content in radioselected H I absorbers and establish a blind-survey benchmark for future studies of molecular gas in H I-selected systems. They also demonstrate that known H I 21 cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.
Euclid quick data release (Q1): XXXVIII. euclid spectroscopy of quasars. 1. identification and redshift determination of 3500 bright quasars
(EDP Sciences, 2026) Karagiannis, Dionysios; Fu, Yuming; Bouwens, Rychard J
The slitless spectroscopy mode of the Near-Infrared Spectrometer and Photometer (NISP) on board the Euclid telescope has enabled efficient spectroscopy of objects within a large field of view. Nevertheless, the relatively low spectral resolution, overlapping spectra, and contamination pose challenges to source classification and redshift determination using the NISP spectra alone. In this work, we present a large and homogeneous sample of bright quasars identified from the Euclid Quick Data Release (Q1), constructed by combining high-purity candidate selections from Gaia and WISE with the new spectroscopic capabilities of Euclid. Through visual inspection of the Euclid spectra of these quasar candidates, we identify approximately 3500 quasars and determine reliable redshifts in the range of 0 < z ≲ 4.8. Of these, 2686 are new spectroscopic identifications relative to existing public compilations. We generated the first Euclid composite spectrum of quasars covering rest-frame near-ultraviolet (NUV) to near-infrared (NIR) wavelengths without telluric lines, which will be pivotal to NIR quasar spectral analysis. We obtained an empirical spectroscopic depth of JE ≲ 21.5 and HE ≲ 21.3 at the sensitivity of the Wide Field Survey, beyond which the number of securely identified quasars declines sharply. Accordingly, the sample presented in this paper comprises spectroscopically confirmed quasars brighter than these limits. We analysed morphological parameters from the Visible Camera (VIS) using Sérsic and model-independent (CAS) metrics, and a deep-learning point spread function fraction (fPSF) to track nuclear dominance. The VIS morphologies show a clear redshift dependence: at low redshift (z < 0.5), obvious host structures are common and a single Sérsic model fits about half of the sources; at intermediate redshift (0.5 < z < 2), the nuclear component dominates, with 90% of the Sérsic fits saturating at the upper index limit. In this intermediate redshift regime, fPSF is available, and we use it as a more reliable compactness measure than the single-Sérsic and CAS parameters to quantify nuclear versus host emission. We also explore the novel Euclid NIR colour space and discuss the role of these quasars in refining active galactic nucleus selection techniques for future Euclid data releases.
HETDEX public data release 1: source catalog 2 and data cubes from ∼90 deg2 of integral-field optical spectroscopy
(American Astronomical Society, 2026) Jarvis, Matt J.; Mentuch Cooper, Erin; Gebhardt, Karl
The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is a wide-field, integral-field spectroscopic survey designed to map the large-scale distribution of Lyα-emitting galaxies (LAEs) at 1.88 < z < 3.52 and constrain dark energy at cosmic noon. Using the 10 m Hobby–Eberly Telescope and the Visible Integral-Field Replicable Unit (IFU) Spectrograph, HETDEX obtains >35,000 spectra per exposure over 3500–5500 Å at R ∼ 800 with (Formula presented) ∼1.″8 image quality, enabling an untargeted census of emission-line galaxies across 540 deg2. We present HETDEX Public Data Release 1 (PDR1), comprising 431,713 IFU observations covering 86.67 deg2 of noncontiguous sky in the Spring (13h, +51°) and Fall (1 (Formula presented) .h 5, 0°) fields, along with legacy regions (Cosmic Evolution Survey, Great Observations Origins Deep Survey North, North Ecliptic Pole, SA22). PDR1 includes the HETDEX Public Source Catalog 2 (HPSC2), an expanded and reprocessed version of E. Mentuch Cooper et al. (2023) incorporating four additional years of data, improved quality control, and new machine learning classifiers. HPSC2 contains 426,654 LAEs, 491,411 [O II] emitters, 19,457 low-z galaxies, 18,303 active galactic nuclei, and 150,608 stars, providing coordinates, redshifts or stellar velocities, and 1D spectra for each source. Because the data cubes use local sky subtraction optimized for faint emission-line detection, they are not suited for absolute surface-brightness measurements or very extended nearby galaxies. Appendix materials include the full detection catalog, the 1.6 million–candidate LAE sample, and raw detection databases. All products are publicly accessible through the HETDEX data portal (https://hetdex.org/data-results/), including access to a public JupyterLab. HPSC2 is also publicly available via Zenodo (doi:10.5281/zenodo.19581262).
Supermightee: spectral ages of remnant radio galaxy candidates in the XMM–LSS field
(Oxford University Press, 2026) Dutta, Sushant; Singh, Veeresh; Wadadekar, Yogesh; Taylor, Russ; Marchetti, Lucia; Vaccari, Mattia; Marchetti, Lucia; Jarvis, Matt; Hale, Catherine; Randriamampandry, Solohery; Randriamanakoto, Zara
Remnant radio galaxies, whose lobes are no longer replenished by jets from the active galactic nucleus (AGN), offer key constraints on AGN duty cycles and the time-scales of radio jets. We present a spectral-ageing study of 14 candidate remnant radio galaxies in the XMM(Formula presented) LSS field, combining new broad-band data from the MeerKAT MIGHTEE ((Formula presented) band) and uGMRT superMIGHTEE (band-3 and band-4) surveys with complementary observations from LOFAR, GMRT, and JVLA, covering 144 MHz(Formula presented) 1.5 GHz. Spectral modelling confirms 12 sources as genuine remnants, while two are reclassified as active, emphasizing the importance of sensitive, multifrequency coverage for robust remnant identification. Pixel-based spectral age maps yield results ((Formula presented) 3–43 Myr) broadly consistent with integrated estimates, revealing relatively short spectral ages ((Formula presented) 8–42 Myr). These ages likely reflect enhanced inverse-Compton losses at higher redshifts (0.35 (Formula presented) z (Formula presented) 2.85; median z = 1.25) and possible rapid lobe expansion in low-density environments. The ratios of remnant to total source ages (t(Formula presented) /t(Formula presented)) span 0.04–0.83, indicating that the sample traces a broad range of evolutionary stages. Our findings reveal a previously underrepresented population of faint, rapidly fading remnants, suggesting that the remnant phase may be shorter and more dynamic than previously thought. This study highlights the crucial role of MIGHTEE and superMIGHTEE surveys in reliably classifying genuine remnants and provides a framework for constraining AGN life cycles in preparation for forthcoming SKA surveys.
Euclid quick data release (q1): xxvii. the strong lensing discovery engine b – early strong lens candidates from visual inspection of high-velocity dispersion galaxies
(EDP Sciences, 2026) Rojas, Karina; Collett, Thomas; Karagiannis, Dionysios
We present a search for strong gravitational lenses in Euclid imaging with a high stellar velocity dispersion (σv > 180 km s−1) reported by SDSS and DESI. We performed expert visual inspection and classification of 11 660 Euclid images. We discovered 38 grade A and 40 grade B candidate lenses, which is consistent with an expected sample of ∼32. Palomar spectroscopy confirmed 5 lens systems, while DESI spectra confirmed one system, provided ambiguous results for another, and helped to discard a third system. The Euclid automated lens modeler modelled 53 candidates, confirmed 38 as lenses, failed to model 9, and ruled out 6 grade B candidates. For the remaining 25 candidates, we were unable to gather additional information. More importantly, our classified non-lenses provide an excellent training set for machine-learning lens classifiers. We created high-fidelity simulations of Euclid lenses by painting realistic lensed sources behind the tagged (non-lens) luminous red galaxies. This training set is the foundation stone for the Euclid galaxy-galaxy strong-lensing discovery engine.
Bayesian component separation and power spectrum estimation for 21 cm intensity mapping data cubes
(Oxford University Press, 2026) Murphy, Geoff G.; Bull, Philip; Santos, Mario G.
Foreground removal remains an ongoing challenge in radio cosmology, and increasingly sensitive experiments necessitate more robust analysis techniques. In this work, we model simulated data from a single-dish intensity mapping experiment, and use the Gibbs sampling and Gaussian constrained realization (GCR) techniques to draw samples from the posterior probability distribution of the model parameters. This allows for a separation of the foregrounds and 21 cm signal at the map level, as well as recovery of the 1-dimensional H i power spectrum to within statistical uncertainties. Despite the model consisting of over 2 million free parameters in the example presented here, these methods allow us to sample from the Bayesian posterior at a rate of (Formula presented) s per iteration. This framework is also resilient to frequency channel flagging (e.g. due to RFI excision), with the GCR steps effectively in-painting the missing data with statistically consistent model realizations. The power spectrum is recovered accurately in the presence of strong foreground contamination and RFI flagging – the estimate falling within (Formula presented) of the true model in our example, similar to the commonly-used transfer function correction method. Statistical realizations of foreground and H i maps are also recovered, with associated uncertainties available from the full joint posterior distribution of all parameters.
Euclid quick data release (q1): xxxv. The role of cosmic connectivity in shaping galaxy clusters
(EDP Sciences, 2026) Karagiannis, Dionysios; Gouin, Céline; Laigle, Clotilde
The matter around galaxy clusters is distributed over several filaments, reflecting their positions as nodes in the large-scale cosmic web. The number of filaments connected to a cluster, i.e. its connectivity, is expected to affect the physical properties of clusters. Using the first Euclid galaxy catalogue from the Euclid Quick Release 1 (Q1), we investigated the connectivity of galaxy clusters and how it correlates with their physical and galaxy member properties. Around 220 clusters located within the three fields of Q1 (covering ∼63 deg2) were analysed in the redshift range 0.2 < z < 0.7. Due to the photometric redshift uncertainty, we reconstructed the cosmic web skeleton, and measured the cluster connectivity, in 2D projected slices with a thickness of 170 comoving h −1 Mpc and centred on each cluster redshift, by using two different filament finder algorithms on the most massive galaxies (M★ > 1010.3 M⊙). In agreement with previous measurements, we recovered the mass-connectivity relation independently of the filament detection algorithm, showing that the most massive clusters are, on average, connected to a larger number of cosmic filaments, consistent with hierarchical structure formation models. Furthermore, we explored the possible correlations between connectivities and two cluster properties: the fraction of early-type galaxies and the Sérsic index of galaxy members. Our result suggests that the clusters populated by early-type galaxies exhibit higher connectivity compared to clusters dominated by late-type galaxies. These preliminary investigations highlight our ability to quantify the impact of the cosmic web’s connectivity on cluster properties with Euclid.
The kinetic Sunyaev Zeldovich effect as a benchmark for AGN feedback models in hydrodynamical simulations: insights from DESI + ACT
(Oxford University Press, 2026) Bigwood, Leah; Dave, Romeel; Yamamoto, Masaya
Baryonic feedback remains one of the largest uncertainties in cosmological hydrodynamical simulations, with different prescriptions producing divergent predictions for the fraction of gas expelled from haloes, the radial extent of the gas expulsion and the impact on large scale matter clustering. We present the first systematic study of the kinetic Sunyaev–Zel’dovich (kSZ) effect across a wide range of simulations (FLAMINGO, ANTILLES, BAHAMAS, SIMBA, FABLE, and their variants), and compare them directly to DESI Year 1 + ACT kSZ measurements. We ensure a like-for-like comparison with observations by developing a robust methodology that accounts for the halo mass selection using galaxy–galaxy lensing, cosmic variance, miscentring, and satellites, establishing the kSZ effect as a new benchmark for the simulations. We find that fiducial feedback models are disfavoured by (Formula presented), while simulations with more powerful active galactic nucleus (AGN) feedback within the FLAMINGO and BAHAMAS suites reproduce the observed kSZ signal within (Formula presented). We use the ANTILLES simulation suite to demonstrate that the amplitude of the kSZ effect is a strong predictor of matter power spectrum suppression, competitive with baryon fraction metrics. This paper clearly demonstrates the potential of kSZ measurements in evaluating feedback physics and for advancing the fidelity of cosmological simulations.
Euclid Quick Data Release (Q1): XXXIX. The evolution of the passive-density and morphology-density relations between z = 0.25 and z = 1
(EDP Sciences, 2026) Karagiannis, Dionysios; Cleland, Cressida; Mei, Simona
The extent to which the environment affects galaxy evolution has been under scrutiny by researchers for decades. With the first data from Euclid, we can begin to systematically study a wide range of environments and their effects as a function of redshift, using 63 deg2 of space-based data. In this paper, we present results from the Euclid Quick Data Release, where we measured the passive-density and morphology-density relations in the redshift range z = 0.25–1. We determined if a galaxy is passive using the specific star formation rate, and we classified the morphologies of galaxies using the Sérsic index n and the u − r colours. We measured the local environmental density of each galaxy using the Nth-nearest neighbour method. We find that at a fixed stellar mass, the quenched fraction (the fraction of galaxies that have ceased star formation) increases with increasing local environmental density up to z = 1. This result is indicative of the separability of the effects from the stellar mass and the environment. Similarly, at all redshifts in this work, the early-type galaxy fraction increases with increasing density at fixed stellar mass, meaning the environment also transforms the morphology of the galaxy independently of stellar mass, up to M* ≲ 1010.8 M⊙. For M* ≳ 1010.8 M⊙, almost all galaxies are early-types, with minimal impact from the environment. At z > 0.75, the morphology depends mostly on stellar mass, with only low-mass galaxies being affected by the environment. Given that the morphology classifications use u − r colours, these are correlated to the star formation rate, and as such our morphology results should be taken with caution, yet future morphology classifications should help verify these results. To summarise, we successfully identify the passive-density and morphology-density relations at 0.25 < z < 1. Future Euclid data releases are key to confirm these trends at higher redshifts.
Experimental gamow–teller strength in the β decay of the rp-process waiting-point nucleus 64Ge and its impact on stellar weak-decay rates
(Elsevier B.V., 2026) Orce, José Nicolás; Nácher E.; Parra, Selene
The β decay of the rp -process waiting-point nucleus 64Ge plays a key role in Type-I X-ray bursts. Reliable theoretical predictions at the high temperatures and densities of these environments require models capable of reproducing the relevant Gamow–Teller (GT) strength under terrestrial conditions. We report a measurement of the B (GT) distribution in the decay of 64Ge using the Total Absorption Gamma-ray Spectroscopy technique at CERN-ISOLDE. The experimentally determined B (GT) distribution is compared with large-scale shell-model calculations and with existing theoretical approaches. While shell-model-based calculations provide a good description of the data, QRPA results show significant discrepancies. Stellar weak-decay rates derived from our experimental B (GT) distribution provide the first experimentally constrained rates for 64Ge, and a stringent benchmark for nuclear-structure models employed in rp-process simulations.
A FLASH HI absorption search in compact sources in the pilot ASKAP interplanetary scintillation field
(Cambridge University Press, 2026) Gordon-Hall, Paris E.; Kerrison, Emily F.; Mahony, Elizabeth K.; Sadler, Elaine M.
In this pilot study, we use data from the First Large Absorption Survey in HI (FLASH) to search for redshifted HI 21 cm absorption at 0.4 < z < 1 towards 157 bright radio sources with Interplanetary Scintillation (IPS) measurements at 820 MHz in a single field observed with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. The ASKAP IPS measurements, which use only 2.5 minutes of observing time in total, allow us to estimate the compactness of these radio sources on sub-arcsecond scales at a frequency within the 712–1000 MHz FLASH band. In particular, the Normalised Scintillation Index (NSI) for each source reflects the fraction of the flux density arising from compact components less than 0.1 arcsec in diameter. We find that 18 ± 5% of ASKAP sources with flux densities above 150 mJy are highly compact with NSI ≥ 0.8 – implying that at least 80% of their radio emission arises from a single region smaller than about 800 pc in size. The compactness of these sources makes them ideal probes for an HI absorption search, since the covering factor for any HI gas clouds along the line of sight is likely to be high. About half of the sources with NSI ≥ 0.8 also have peaked radio spectral energy distributions (SEDs), consistent with previous IPS studies at lower frequencies. These pilot results imply that IPS measurements with ASKAP can provide a simple and powerful tool for identifying uniform samples of compact radio sources at frequencies of a few hundred MHz across large areas of sky. With FLASH, we detect two new HI absorption lines against compact sources in the ∼ 30 deg2 region of sky covered by the IPS data; an associated HI line at redshift z = 0.9540 (with a matching optical redshift) in MRC 2125-237 (NSI = 0.98), and a likely intervening line at z = 0.4632 towards MRC 2131-241 (NSI = 0.84). The radio sources with these two detections are both bright and compact, with peaked radio SEDs.
A fully photometric approach to type Ia supernova cosmology in the LSST era: host-galaxy redshifts and supernova classification
(American Astronomical Society, 2026) Lochner, Michelle; Mitra, Ayan; Kessler, Richard
The upcoming Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) is expected to discover nearly one million Type Ia supernovae (SNe Ia), offering an unprecedented opportunity to constrain dark energy. The vast majority of these events will lack spectroscopic classification and redshifts, necessitating a fully photometric approach to maximize cosmology constraining power. We present detailed simulations based on the Extended LSST Astronomical Time Series Classification Challenge, and a cosmological analysis using photometrically classified SNe Ia with host-galaxy photometric redshifts. This dataset features realistic multiband light curves, non–SN Ia contamination, host mis-associations, and transient–host correlations across the high-redshift Deep Drilling Fields (∼50 deg2). We also include a spectroscopically confirmed low-redshift sample based on the Wide Fast Deep fields. We employ a joint SN + host photometric redshift fit, a neural-network-based photometric classifier (Supernova Classification with a Convolutional Neural Network), and the Bayesian Estimation Applied to Multiple Species with Bias Corrections methodology to construct a bias-corrected Hubble diagram. We produce statistical + systematic covariance matrices, and perform cosmology fitting with a prior using cosmic microwave background constraints. We fit and present results for the wCDM dark energy model and the more general Chevallier–Polarski–Linder w0waCDM model. With a simulated sample of ∼6000 events, we achieve a figure of merit (FoM) value of about 150, which is significantly larger than the DES-SN5YR FoM of 54. Averaging the analysis results over 25 independent samples, we find small but significant biases indicating a need for further analysis testing and development.
Mixing of structures in100zr studied via β decay
(Jagiellonian University, 2026) Kalaydjieva, Desislava; Bildstein, V; Garrett, P.E; Zielińska, M; Stoychev, K; Rocchini, M; Pannu, S; Bidaman, H; Korten, W; Vedia, V; Garnsworthy, A.B; Ahmed, Z; Andreoiu, C; Annen, D.W; Asch, H; Avaa, A.A; Ball, G.C; Benzoni, G; Bhattacharjee, S.S; Buck, S; Coleman, R.J; Devinyak, S; Dillmann, I; Dowie, J; Caballero-Folch, R; Garcia, F.H; Geerlof, E.D; Greaves, B; Griffin, C.J; Grimes, A.L; Grinyer, G.F; Gyabeng Fuakye, E; Hackman, G; Hicks, S; Hymers, D; Kanungo, R; Kapoor, K; Karayonchev, V; Kasanda, E; Lange, S; Lenardo, B; Maqungo, Lwazikazi; Marchini, N; Marlow, B; Martin, M.S; Mashtakov, K.M; Murillo Morales, S; Murias, J.R; Nannini, A; Natzke, C; Olaizola, B; Ortner, K; Peters, E; Petrache, C.M; Polletini, M; Porzio, C; Radich, A.J; Richardson, G; Saei, N; Satrazani, M; Scheck, M; Siciliano, M; Singh, M; Spagnoletti, P; Svensson, C.E; Taddei, E; Tocabens, G; Torres, D.A; Triambak, Smarajit; Umashankar, R; Valbuena, S; Wu, F; Zidar, T
Properties of low-lying states in100Zr were studied using the GRIFFIN spectrometer at TRIUMF following the β decay of100Y. Using γ–γ angular correlations, level spins were confirmed and E2/M1 mixing ratios determined with improved precision. Applicability of a two-state mixing model to the observed structures in100Zr is explored.
Euclid quick data release (q1) Xix. First study of red quasars selection
(EDP Sciences, 2026) Karagiannis , Dionysios; Tarsitano , Federica; Fotopoulou , Sotiria; Banerji , Manda
Red quasars constitute an important but elusive phase in the evolution of supermassive black holes, where dust obscuration can significantly alter their observed properties. They have broad emission lines, like other quasars, but their optical continuum emission is significantly reddened, which is why they were traditionally identified based on near- and mid-infrared selection criteria. This work showcases the capability of the Euclid space telescope to find a large sample of red quasars, using Euclid near infrared (NIR) photometry. We first conduct a forecast analysis, comparing a synthetic catalogue of red quasars with COSMOS2020. Using template fitting, we reconstruct Euclid-like photometry for the COSMOS sources and identify a sample of candidates in a multi-dimensional colour-colour space achieving 98% completeness for mock red quasars with 30% contaminants. To refine our selection function, we implement a probabilistic Random Forest classifier, and use UMAP visualisation to disentangle non-linear features in colour-space, reaching 98% completeness and 88% purity. A preliminary analysis of the candidates in the Euclid Deep Field Fornax (EDF-F) shows that, compared to VISTA+DECam-based colour selection criteria, Euclid’s superior depth, resolution, and optical-to-NIR coverage improves the identification of the reddest, most obscured sources. Notably, the Euclid exquisite resolution in the IE filter unveils the presence of a candidate dual quasar system, highlighting the potential for this mission to contribute to future studies on the population of dual AGN. The resulting catalogue of candidates, including more the 150 000 sources, provides a first census of red quasars in Euclid Q1 and sets the groundwork for future studies in the Euclid Wide Survey (EWS), including spectral follow-up analyses and host morphology characterisation
Euclid quick data release (Q1): XV. A probabilistic classification of quenched galaxies
(EDP Sciences, 2026) Karagiannis, Dionysios; Corcho-Caballero, Pablo; Ascasibar, Yago
Investigating what drives the quenching of star formation in galaxies is key to understanding their evolution. The Euclid mission will provide rich spatial and spectral data from optical to infrared wavelengths for millions of galaxies, and enable precise measurements of their star formation histories. Using the first Euclid Quick Data Release (Q1), we developed a probabilistic classification framework that combines the average specific star-formation rate (sSFRlog(τ)) inferred over two timescales (τ = 108, 109 yr) to categorise galaxies as ‘ageing’ (secularly evolving), ‘quenched’ (recently halted star formation), or ‘retired’ (dominated by old stars). We validated this methodology using synthetic observations from the IllustrisTNG simulation. Two classification methods were employed: a probabilistic approach, which integrates posterior distributions, and a model-driven method, which optimises sample purity and completeness using IllustrisTNG. At z < 0.1 and M* ≳ 3 × 108 M⊙, we obtain Euclid class fractions of 68–72%, 8–17%, and 14–19% for ageing, quenched, and retired populations, respectively, which is consistent with previous studies. Ageing and retired galaxies dominate at the low- and high-mass end, respectively, while quenched galaxies surpass the retired fraction for M* ≲ 1010 M⊙. The evolution with redshift shows increasing and decreasing fractions of ageing and retired galaxies, respectively. The fraction of quenched systems shows a weaker dependence on stellar mass and redshift, varying between 5 and 15%. We find tentative evidence that more massive galaxies usually undergo quenching episodes at earlier times with respect to their low-mass counterparts. We analysed the mass-size-metallicity relation for each population. Ageing galaxies generally exhibit disc morphologies and low metallicities. Retired galaxies show compact structures and enhanced chemical enrichment, while quenched galaxies form an intermediate population that is more compact and chemically evolved than ageing systems. Despite potential selection biases, this work demonstrates Euclid’s great potential for elucidating the physical nature of the quenching mechanisms that govern galaxy evolution.
Euclid Quick Data Release (Q1): XXXII. From simulations to sky: Advancing machine-learning lens detection with real Euclid data
(EDP Sciences, 2026) Lines, Natalie; Collett, Thomas; Karagiannis, Dionysios
In the era of large-scale surveys such as Euclid, machine learning has become an essential tool for identifying rare yet scientifically valuable objects, such as strong gravitational lenses. However, supervised machine-learning approaches require large quantities of labelled examples to train on, and the limited number of known strong lenses has led to a reliance on simulations for training. A well-known challenge is that machine-learning models trained on one data domain often underperform when applied to a different domain: in the context of lens finding, this means that strong performance on simulated lenses does not necessarily translate into equally good performance on real observations. In the Euclid Quick Data Release 1 (Q1), covering 63 deg2, 500 strong lens candidates were discovered through a synergy of machine learning, citizen science, and expert visual inspection. These discoveries now allow us to quantify this performance gap and investigate the impact of training on real data. We find that a network trained only on simulations recovers up to 92% of simulated lenses with 100% purity, but only achieves 50% completeness with 24% purity on real Euclid data. By augmenting training data with real Euclid lenses and non-lenses, completeness improves by 25–30% in terms of the expected yield of discoverable lenses in the Euclid Data Release 1 and the full Euclid Wide Survey. Roughly 20% of this improvement comes from the inclusion of real lenses in the training data, while 5–10% comes from exposure to a more diverse set of non-lenses and false positives from Q1. We show that the most effective lens-finding strategy for real-world performance combines the diversity of simulations with the fidelity of real lenses. This hybrid approach establishes a clear methodology for maximising lens discoveries in future data releases from Euclid and will likely also be applicable to other surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time.

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