arXiv subjects

M. Brescia

Publications and source records attributed to M. Brescia.

At least 19 recordsLinked to original sources

arXiv2026

Euclid Quick Data Release (Q1). Mass-to-light ratio of elliptical galaxies: constraints from strong lensing

Mass is among the most fundamental properties describing a galaxy. The relation between the luminosity and the total mass of a galaxy contains information on the efficiency of the star formation process and on the distribution of dark matter. We used strong gravitational lensing data from the Euclid Quick Data Release 1 (Q1) to constrain the total mass enclosed within an aperture of $5\,h^{-1}$kpc, $M_5$, of elliptical galaxies. Our analysis is based on a sample of 95 lenses, which we built by ensuring that their selection function is reproducible. This enabled us to correct our inference for selection effects. The average $\log_{10}{(M_5\,h\,M_\odot^{-1})}$ for a galaxy with an $r$-band luminosity of $10^{10.7}L_{\odot}\,h^{-2}$ at $z=0.5$ is $11.30\pm0.02$. The mass $M_5$ scales with luminosity to the power $β_\mathrm{L}=0.71\pm0.07$, and decreases with increasing redshift at fixed luminosity. Assuming a scenario in which galaxies grow by mergers and stellar populations evolve passively, these correlations imply that $M_5$ increases with time for individual galaxies. These measurements provide a useful benchmark for testing models of galaxy structure and evolution that make predictions on the distribution of total mass on the scales of $5\,h^{-1}$kpc.

astro-ph.GA↗

arXiv2026

Model-independent calibration of gamma-ray bursts with Bayesian neural networks

Context. Gamma-ray bursts (GRBs) extend cosmological distance measurements beyond the range densely sampled by Type Ia supernovae, but their standardization requires reliable calibration and uncertainty estimates. Aims. We calibrate the Amati correlation without assuming a background cosmological model, assess its stability, and examine the cosmological reach of current and future GRB Hubble diagrams. Methods. We train a Bayesian neural network on Pantheon+ supernovae, assess and recalibrate its predictive uncertainties, and calibrate the correlation for GRBs at $z \leq 1.5$ using the D'Agostini and Reichart likelihoods. We combine the GRB Hubble diagram with supernovae, Hubble-parameter measurements, and DESI baryon acoustic oscillations. Local-regression, covariance, leave-three-out, redshift-evolution, and Efron-Petrosian diagnostics test the standardization assumptions. We also analyse idealized future catalogues of 1500 standardized GRBs. Results. The diagram reaches $z \simeq 9.4$. Covariance and leave-three-out diagnostics produce small changes in the cosmological constraints. A parametric evolution coefficient is consistent with zero, whereas the truncation-corrected diagnostic indicates marginal isotropic-energy evolution that can occur along the Amati relation. Dark-energy extensions improve the phenomenological fit relative to flat $Λ$CDM: AIC favours the Chevallier-Polarski-Linder parametrization, while BIC favours constant-$w$ dark energy. Forecasts show strong conditional model-discrimination power under the adopted uncertainty model. Conclusions. GRBs provide a complementary high-redshift extension of the supernova distance ladder. Present results do not establish an evolving dark-energy equation of state. Larger homogeneous samples are promising, but realistic selection functions and calibration systematics remain essential.

astro-ph.CO↗

arXiv2026

Euclid: Quick Data Release (Q1) -- Ultracool dwarfs in the Euclid Deep Fields

Ultracool dwarfs (UCDs) encompass the lowest-mass stars and brown dwarfs at the substellar boundary. These intrinsically faint objects are challenging to detect, but the wide coverage and deep sensitivity of the Euclid survey increase confirmed UCD counts by orders of magnitude. We carried out a systematic study using Euclid Quick Data Release (Q1) low-resolution near-infrared spectra to identify and characterise UCDs. A sample of previously known UCDs in Q1 validated the analysis, which was then applied to newly identified UCD candidates in Euclid Deep Field North (EDF-N; 22.9 deg^2, down to J_E ~ 24.5 mag). We confirm 33 new UCDs in EDF-N, spanning spectral types M7-T1 (J_E = 17-21 mag) and distances of 50-600 pc. Two objects were followed up with optical and NIR observations using the Gran Telescopio Canarias, providing independent validation of Euclid classifications. We determined spectral types for 33 new UCDs and 167 previously known UCDs by fitting SpeX Prism Library Analysis Toolkit standards. The known sample includes 103 Dark Energy Survey objects (M7-T0, J_E = 17-22 mag), 6 literature sources (M8-T7, J_E = 18-20 mag), and 58 Gaia sources (M7-L1, J_E = 17-24 mag). Independent stellar parameters from atmospheric model fitting agree well with Euclid spectral types. We also investigated Gaia UCDs in Q1 by combining mean XP spectra with Euclid NIR spectra to determine radii. We present a publicly available catalogue including observations, classifications, and stellar parameters. This work demonstrates Euclid's capability to characterise faint stellar populations, establishing a foundation for large-scale UCD studies.

astro-ph.SR↗

arXiv2026

The Conjugacy Problem for Recursively Presented Virtually Soluble Groups of Finite Prüfer Rank

We solve a long-standing conjugacy problem for finitely presented soluble groups of finite Prüfer rank, recorded as Problem~9.52 in the Kourovka Notebook, in the stronger setting of recursively presented finitely generated virtually soluble groups. Robinson proved that, in every recursively presented finitely generated virtually soluble minimax group, conjugacy to any fixed element is decidable, while explicitly lefting open whether the procedure could be made uniform in the target element. We establish this uniformity. More specifically, we prove that every recursively presented finitely generated virtually soluble group of finite Prüfer rank has decidable Conjugacy Problem.

math.GR↗

arXiv2026

Euclid Quick Data Release (Q1). Data processing for intracluster light measurements

The Euclid survey provides images with extraordinary potential for studies of the low-surface-brightness Universe, including intracluster light (ICL). However, to realise this promise, the data must be carefully treated to minimise background variations while preserving the signal from diffuse structures. In this work, we describe the post-processing and measurement procedures used for studies of ICL with Euclid. We demonstrate that we are able to substantially reduce background variations without resorting to a small-scale background subtraction. By injecting simulated clusters into the real images, we show that our approach preserves the faint outskirts of extended sources. On scales of several arcminutes, we can reliably detect surface-brightness levels around 27.5 mag arcsec$^{-2}$ in $Y_\textrm{E}$, $J_\textrm{E}$, $H_\textrm{E}$, and 29 mag arcsec$^{-2}$ in $I_\textrm{E}$. As a result, we can obtain accurate measurements of the ICL in individual clusters from the local Universe out to z~0.8 with uncertainties on the order of 10% in surface brightness, 10 degrees in position angle, and 0.1 in ellipticity. Our ability to measure the diffuse light with Euclid is thus set to meet expectations and revolutionise our understanding of the ICL.

astro-ph.GA↗

arXiv2026

Euclid Quick Data Release (Q1). The shape of cluster haloes revealed by intracluster light

Intracluster light (ICL) offers a luminous route for measuring the shapes and orientations of cluster haloes. We used Euclid Quick Data Release (Q1) images to quantify ICL shapes for 205 clusters at $0.1 \leq z \leq 0.8$ selected from the eROSITA All-Sky Survey and the Dark Energy Survey. We measured the ICL properties across five bands ($I_\mathrm{E}$, $Y_\mathrm{E}$, $J_\mathrm{E}$, $H_\mathrm{E}$ and the coadded $YJH_\mathrm{E}$), and find that the shape parameters are consistent across the filters, with the $H_\mathrm{E}$ band probing the profiles to the largest cluster-centric distances ($0.1R_{200\mathrm{c}}\sim100$ kpc). The ICL ellipticity ($e=1-b/a$) distribution peaks at 0.5, consistent with halo ellipticities inferred from strong and weak lensing studies, suggesting that the ICL traces the large-scale structure of the clusters. Cluster cores, dominated by brightest cluster galaxy (BCG) light, are round ($e\sim0.2$), while the ICL becomes progressively more elongated at large radii, reaching an ellipticity of $\sim0.5$ by $0.1R_{200\mathrm{c}}$. We find that the ICL is closely aligned with the BCG (87% lie within 30$^\circ$), but shows a weaker alignment with the satellite galaxy distribution (61% within 30$^\circ$). Robust position angles could be measured using the ICL for 63% of the sample, whereas position angles could be measured for only 30% of the sample using the satellite galaxies. Stacking clusters in redshift bins allows measurements of the ICL surface brightness to $0.6$-$0.8R_{200\mathrm{c}}$ and ellipticity beyond $0.3$-$0.4R_{200\mathrm{c}}$ (300-400 kpc), but we observed a plateau in the ICL ellipticity beyond $0.1R_{200\mathrm{c}}$. These results demonstrate the capability of Euclid to characterise the ICL morphology with high statistical precision, allowing new constraints on cluster halo structure and its evolution with redshift.

astro-ph.GA↗

arXiv2026

Euclid Quick Data Release (Q1). A systematic study of the intracluster light fraction at 0.2 < z < 1.5

We present a homogeneous analysis of the intracluster light (ICL) in approximately 300 galaxy clusters spanning $0.2 10^{10}\,M_\odot$). The inferred ICL fraction also depends systematically on wavelength, while remaining largely insensitive to the adopted outer integration radius of 200-600 kpc. These results highlight the importance of homogeneous ICL analyses and constrain the evolution of diffuse stellar components in clusters.

astro-ph.GA↗

arXiv2026

Euclid Quick Data Release (Q1). The metallicity of the intracluster light

Colour provides key information to constrain the stellar population of the intracluster light (ICL), the diffuse light within galaxy clusters. We derive radial colour profiles ($Y_\mathrm{E}-H_\mathrm{E}$, $J_\mathrm{E}-H_\mathrm{E}$, $I_\mathrm{E}-H_\mathrm{E}$) of the brightest central galaxy (BCG) and ICL for 168 galaxy clusters from the Dark Energy Survey redMaPPer catalogue within the redshift range $0.1 < z < 0.75$ and halo mass $M_{\rm 200m} > 10^{14.05}M_\odot/h$, within the Euclid Quick Data Release (Q1). By stacking the light profiles measured using elliptical annuli on the BCG and ICL images, we reliably measure the ICL colour out to approximately 300 kpc, over which we find a colour gradient, with the ICL becoming bluer than the BCG out to approximately 150 kpc. Using stellar population synthesis (SPS) models, we find that near-infrared (NIR) colours are sensitive to metallicity, but not age. Thus, we measure a metallicity profile in the BCG and ICL that extends out to 300 kpc for a statistical sample for the first time. While the colours, and the detection of a colour and metallicity gradient, are robust, we note that our metallicity measurement is dependent upon our choice of both SPS model and colour. We find that the metallicity of the BCG is super-solar [$\log_{10} (Z/Z_\odot) > 0.1$], while the ICL is metal-poor [$\log_{10}(Z/Z_\odot)\approx -0.5$], placing the first statistical constraint on the metallicity of the ICL out to large radii. These results support our current understanding of BCG and ICL formation: BCGs form predominantly through mergers with massive galaxies or the cores of satellite galaxies, while the ICL grows via the tidal stripping of lower-metallicity stars from the outskirts of massive satellite galaxies.

astro-ph.GA↗

arXiv2026

Euclid Bypass end-to-end simulations for spectroscopic galaxy clustering performance assessment

We present a simulation framework for Euclid galaxy clustering measurements that reproduces the essential behaviour of the spectroscopic reduction chain, bypassing the computation required by full pixel-level simulations. The framework comprises two complementary tools, FastSpec, which simulates 1-dimensional slitless spectra with a simplified instrument and noise model, and Pypelid, which computes detection probabilities on input catalogues, accounting for the survey dithering sequence and spatially varying noise. We develop calibrated prescriptions for the survey selection function, redshift errors, and redshift interloper populations. Applied to the Euclid Wide Survey, the baseline selection yields a redshift purity of 74% and a sample completeness of 45%, which improves with the use of Euclid photometric colours. The redshift error distribution is found to have a Gaussian core of width $σ_z = 9.4 \times 10^{-4}$, with no significant trend over $0.9 < z < 1.8$. Emission lines [OIII]5008 and [SIII]9530 misidentified as H$α$ contribute a few to ten per cent depending on redshift, while catastrophic redshift measurement failures dominate at low signal-to-noise ratio. Simulating the Data Release 1 footprint, we find that complex survey selection effects can be corrected with a forward-modelled random catalogue, recovering the monopole and quadrupole of the galaxy 2-point correlation function. The simplified noise model does not include residual contamination from overlapping spectra, or other artefacts seen in early Euclid data; this will be revisited with DR1 data. The framework provides an efficient route for characterising the Euclid spectroscopic selection function at the precision required for galaxy clustering science, and is the basis for systematic error assessments in Euclid galaxy clustering analyses.

astro-ph.CO↗

arXiv2026

The GAGE survey. I. Deep multi-band stellar variability characterization and automated classification toward Baade's window

Context. Long-term photometric surveys of the Galactic bulge are vital for characterizing its stellar populations and structure, providing a foundation for next-generation facilities. Aims. We present initial results of the GalActic bulGe with plEiadi (GAGE) project, focusing on variable star discovery in Baade's Window. Methods. Using archival DECam (ugriz) data on the Blanco 4-m Telescope spanning six years, we applied high-precision PSF photometry. We developed a pipeline combining Generalized Lomb-Scargle analysis and polynomial light-curve modelling to derive mean multi-band magnitudes and amplitudes. Results. Quality cuts yield 6,304 high-confidence variable sources. We expand multi-band coverage for 4,568 sources in common with OGLE IV and uncover 1,736 (~28%) new candidates absent from OGLE IV. Using a Random Forest classifier, we categorize these sources, finding that 1,391 were also missing from both Gaia DR3 and VVV. This population is concentrated at the fainter end (i >= 17.5 mag), enabled by our deeper detection limits. Conclusions. Our pipeline effectively probes deep, highly crowded fields, expanding the variable star inventory of the inner Galaxy as a benchmark for Rubin-LSST.

astro-ph.SR↗

arXiv2026

Euclid Quick Data Release (Q1). Exploring the complexity of quenching processes across time, environment, and mass through recently quenched galaxies

Recently quenched galaxies (RQGs) provide insights into galaxy quenching. We present a photometric and spectroscopic analysis of RQGs using the first Euclid Quick Data Release (Q1). Using rest-frame UVJ colours, we classify star-forming (SFGs), quiescent (QGs), and recently quenched galaxies at 0.2 0.5, suggesting earlier quenching in dense regions. RQGs show intermediate properties between SFGs and QGs in stellar mass, star-formation rate, specific star-formation rate, Sersic index, and radius. Most RQGs exhibit regular morphologies, excluding merger as a primary mechanism. We find that fRQGs retain disc-like morphologies, whereas sRQGs are more concentrated, suggesting different stages of morphological transformation. Our analysis suggests that multiple mechanisms drive quenching. Stacked spectra of galaxies with spectroscopic redshifts confirm old, passive populations in QGs, while sRQG spectrum shows weak Ha emission, indicating residual star-formation activity or AGN contribution. The recently-quenched nature of RQGs is confirmed by strong Balmer absorption lines in stack DESI spectra. The stacked Euclid QG spectrum agrees with previous templates and stellar population models older than 5Gyr at z<1. These results demonstrate Euclid's potential for studying galaxy quenching, to be further enhanced by future releases.[Abrg.]

astro-ph.GA↗

arXiv2026

Euclid: Impact of halo mass-conversion model assumptions on galaxy cluster number-count analyses

The large catalogues of galaxy clusters expected from the Euclid survey will enable cosmological analyses of cluster number counts that require accurate cosmological model predictions. One possibility is to use parametric fits calibrated against $N$-body simulations, that capture the cosmological parameter dependence of the halo mass function. Several studies have shown that this can be obtained through a calibration against haloes with spherical masses defined at the virial overdensity. In contrast, if different mass definitions are used for the HMF and the scaling relation, a mapping between them is required. Here, we investigate the impact of such a mapping on the cosmological parameter constraints inferred from galaxy cluster number counts. Using synthetic data from $N$-body simulations, we show that the standard approach, which relies on assuming a concentration-mass relation, can introduce significant systematic bias. In particular, depending on the mass definition and the relation assumed, this can lead to biased constraints at more than 2$σ$ level. In contrast, we find that in all the cases we have considered, the mass conversion based on the halo sparsity statistics result in a systematic bias smaller than the statistical error.

astro-ph.CO↗

arXiv2026

The group class SJ is not countably recognizable

A group is an {\it $\SJ$-group} if it admits a general abelian series all of whose terms are subnormal of finite defect in the whole group. We construct a group $G$ which is not an~\hbox{$\SJ$-group}, although every countable subgroup of $G$ is an $\SJ$-group.

math.GR↗

arXiv2026

Euclid preparation CIX. Baryon acoustic oscillation analysis of photometric galaxy clustering in configuration space

With about 1.5 billion galaxies expected to be observed, the very large number of objects in the Euclid photometric survey will allow for precise studies of galaxy clustering from a single survey, over a large range of redshifts $0.2 < z < 2.5$. In this work, we use photometric redshifts to extract the baryon acoustic oscillation signal (BAO) from the Flagship galaxy mock catalogue with a tomographic approach to constrain the evolution of the Universe and infer its cosmological parameters. We measured the two-point angular correlation function in 13 redshift bins. A template-fitting approach was applied to the measurement to extract the shift of the BAO peak through the transverse Alcock-Paczynski parameter $α$. A joint analysis of all redshift bins was performed to constrain $α$ at the effective redshift $z_\mathrm{eff}=0.77$ with MCMC and profile likelihood techniques. We also extracted one $α_i$ parameter per redshift bin to quantify its evolution as a function of time. From these 13 $α_i$, which are directly proportional to the ratio $D_\mathrm{A}/r_\mathrm{d}$, we constrain the product $h\,r_\mathrm{d}$ and $Ω_\mathrm{m}$. From the joint analysis, we constrain $D_\mathrm{A}/r_\mathrm{d}=10.764^{+0.0839}_{-0.0849}$, a three-fold improvement over current constraints from the Dark Energy Survey. As expected, the constraining power in the analysis of each redshift bin is lower, with an uncertainty ranging from $\pm\,1.23$ to $\pm\,0.289$. From these results, we constrain $Ω_\mathrm{m}=0.296^{+0.074}_{-0.059}$ and $h\,r_\mathrm{d}=99.35^{+4.29}_{-4.55}\,\mathrm{Mpc}$. We quantify the influence of analysis choices such as the template, scale cuts, redshift bins, and systematic effects such as redshift-space distortions, over our constraints, both at the level of the extracted $α_i$ parameters and at the level of cosmological inference.

astro-ph.CO↗

arXiv2026

Euclid preparation. Testing analytic models of galaxy intrinsic alignments in the Euclid Flagship simulation

We model intrinsic alignments (IA) in Euclid's Flagship simulation to investigate its impact on Euclid's weak lensing signal. Our IA implementation in the Flagship simulation takes into account photometric properties of galaxies as well as their dark matter host halos. We compare simulations against theory predictions, determining the parameters of two of the most widely used IA models: the Non Linear Alignment (NLA) and the Tidal Alignment and Tidal Torquing (TATT) models. We measure the amplitude of the simulated IA signal as a function of galaxy magnitude and colour in the redshift range $0.1<z<2.1$. We find that both NLA and TATT can accurately describe the IA signal in the simulation down to scales of $6$-$7 \,h^{-1}\,$Mpc. We measure alignment amplitudes for red galaxies comparable to those of the observations, with samples not used in the calibration procedure. For blue galaxies, our constraints are consistent with zero alignments in our first redshift bin $0.1 < z < 0.3$, but we detect a non-negligible signal at higher redshift, which is, however, consistent with the upper limits set by observational constraints. Additionally, several hydrodynamical simulations predict alignment for spiral galaxies, in agreement with our findings. Finally, the evolution of alignment with redshift is realistic and comparable to that determined in the observations. However, we find that the commonly adopted redshift power-law for IA fails to reproduce the simulation alignments above $z=1.1$. A significantly better agreement is obtained when a luminosity dependence is included, capturing the intrinsic luminosity evolution with redshift in magnitude-limited surveys. We conclude that the Flagship IA simulation is a useful tool for translating current IA constraints into predictions for IA contamination of Euclid-like samples.

astro-ph.CO↗

arXiv2026

Euclid Quick Data Release (Q1). The first Euclid view of Planck galaxy protocluster candidates at cosmic noon

[ABRIGED ABSTRACT] A large catalogue of candidate galaxy protoclusters with high star-formation rates was produced by the Planck collaboration. We search, in the first data release (Q1) of the Euclid survey, for the visible and infrared counterparts of the Planck galaxy protocluster candidates expected to be above $z > 1.5$. Eight of them are in Euclid Q1. Our goal is to investigate the optical nature of these overdensities previously detected in the submillimetre wavelength range. We search for overdensities using the DETECTIFz algorithm, an overdensity finder based on Delaunay tessellation that uses photometric redshift probability distributions through Monte Carlo simulations. Focusing our search on the eight high-star forming Planck protocluster candidates, we find that two of them have one Euclid counterpart, and six have between two and four Euclid counterparts, which amounts to a total of 20 Euclid counterparts. These Euclid counterparts lie at photometric redshifts $1.4<z_{\rm ph} < 2.7$ and 12 of them also have partial Herschel coverage. All detections have also been confirmed by at least one other independent protocluster detection algorithm. We study the colours, derived stellar masses and star-formation rates (SFRs) of the detected member galaxies of those protocluster candidate counterparts. We also estimate the total stellar masses, SFRs, and the halo mass lower limits for all Euclid protocluster candidates. We find that in the dark matter halo mass ($M_{\rm h}$) / redshift plane, these Planck and Euclid overdense regions lie in the region $12.6 <\log_{10} (M_{\rm h}/M_\odot)< 13.4$, $1.4<z< 2.7$. This means that the halos of our objects are expected to have experienced a transition between cold flows in hot media to accretion of hot material.

astro-ph.CO↗

arXiv2026

Euclid: Disky titans - surprisingly high star formation activity and gas content in two brightest group galaxies at z~0.75

We present the discovery of two disky titans in the first data release of the Euclid satellite. These sources are massive (M>10^11 Msun) star-forming (SFR~20 Msun/yr) discs located in strong over-densities at intermediate redshift (z~0.75). They represent an small fraction of the massive galaxies in over-dense regions (just four candidates in more than 20 deg2 analysed in this study), and their existence is puzzling considering the abundance of passive and bulge-dominated sources commonly found at the centre of groups and clusters at low redshift. Firstly, our analysis shows that these objects are located in massive groups (Mh~10^13.8 Msun), where rapid accretion of cold gas should be prevented from the formation of a static hot halo. Despite this, a millimetre follow-up with NOEMA shows significant cold gas reservoirs (M_h2~10^10.3 Msun) within these sources. Secondly, our morphological analysis shows the presence of a massive and passive bulge in these galaxies, which is expected to stabilise the disc against fragmentation thereby suppressing further star formation. However, these sources lie on the Schmidt-Kennicutt relation or even slightly above. Building on these observations, we propose a scenario where these disky titans are the product of a merger-induced rejuvenation episode, in which the most massive galaxy of a group accretes cold gas from another member and briefly restarts star-formation. Such scenario is supported by a comparison with the TNG300 simulation and easily explains the surviving of star-formation activity in massive galaxies in over-dense environments as temporary stages in a more complex evolution. More in general, our study showcases the ability of Euclid to find rare objects thanks to the unprecedented statistics offered by its surveys and the scientific potential residing in the synergy between Euclid and other facilities observing at longer wavelengths.

astro-ph.GA↗

arXiv2026

Euclid preparation. XCV. Cosmology Likelihood for Observables in Euclid (CLOE). 2. Code implementation

We provide a description of the code implementation and structure of Cosmology Likelihood for Observables in Euclid (CLOE), developed by members of the Euclid Consortium. CLOE is a modular Python code for computing the theoretical predictions of cosmological observables and evaluating them against state-of-the-art data from galaxy surveys such as Euclid in a unified likelihood. This primarily includes the core observables of weak gravitational lensing, photometric galaxy clustering, galaxy-galaxy lensing, and spectroscopic galaxy clustering, but also extended probes such as the clusters of galaxies and cross-correlations of galaxy positions and shapes with the cosmic microwave background. While CLOE has been developed to serve as the unified framework for the parameter inferences in Euclid, it has general capabilities that can serve the broader cosmological community. It is different from other comparable cosmological tools in that it is written entirely in Python, performs the full likelihood calculation, and includes both photometric and spectroscopic observables. We focus on the primary probes of Euclid and describe the overall code structure, rigorous code development practices, extensive documentation, unique features, speed optimization, and future development plans. CLOE is publicly available at https://github.com/cloe-org/cloe.

astro-ph.CO↗