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M. Brescia

Publications and source records attributed to M. Brescia.

At least 19 recordsLinked to original sources
arXiv2026

Euclid: Survey mask effects on clustering of galaxy clusters

Wide-area cluster catalogues from Stage-IV surveys will substantially improve the precision of cluster clustering measurements, making the control of observational systematic effects essential for cosmological inference. In preparation for the first Euclid data release (DR1), we assess the impact of the survey mask and non-homogeneous sky coverage on the two-point correlation function of galaxy clusters and its covariance. Using DR1-like lightcone mocks, we confirm that the irregular footprint does not introduce appreciable changes in the two-point correlation function when the same mask is applied to the random catalogue. We also find that spatial inhomogeneities, implemented as variations of the cluster selection function in different patches of the sky, do not significantly bias the clustering amplitude, up to levels of variation well above those expected for DR1. When the degree of inhomogeneity is increased to the regime where the effect becomes significant, we show that its amplitude is related to the maximum variation of the selection function among different regions, rather than to the number of such regions. We further find that irregular mask geometry and non-uniform sky coverage both increase the clustering covariance, introducing small, nearly scale-independent offsets that can be captured by nuisance parameters in the covariance model. Our results consolidate the treatment of mask systematic errors for DR1 and inform the methodological refinements required for future \Euclid cluster cosmology.

astro-ph.CO↗
arXiv2026

Euclid Quick Data Release (Q1). Refining the strong lens sample with Space Warps crowd-sourced science

We demonstrate the efficacy of crowd-sourced refinement of strong gravitational lens candidate samples by citizen scientists. Binary (lens/non-lens) classification by citizen scientists has been conducted previously, and here we extend such categorisation into `definite', `probable', `possible', and `non-lenses'. This grading is a required stage ahead of any strong lens sample publication and is usually carried out by (small) teams of researchers. We compare the responses of the volunteers to those of strong lens researchers and discuss the optimal strategy for lens classification and grading in future strong lens searches. Volunteers are found to be able to correctly identify systems of each grade, and their responses can be calibrated to be comparable to those of researchers. Grade posteriors, defined as the probability that a strong lens system classified by the volunteers is a certain grade, converge most rapidly for non-lens systems. We find that one researcher classification is equivalent to only 1.9 volunteer classifications when grading such systems. There is significant disagreement in the grading of intermediate-grade lens candidates amongst both volunteers and researchers. Moving towards calibrated lens probabilities for future lens searches would help to account for such subjectivity. If the Q1 lens search was rerun with volunteers performing lens grading (and corresponding calibration), a completeness of 79% for Grades A+B (corresponding to definite + probable lenses respectively) could be achieved with 41% purity prior to researcher inspection - this would correspond to an expected 12500 true lenses (i.e. excluding contaminants) in Euclid DR1.

astro-ph.GA↗
arXiv2026

Euclid: Modelling observational effects in cluster counts and cluster clustering

This study explores the impact of observational and modelling systematic effects on cluster number counts and cluster clustering and provides model prescriptions for their joint analysis in the context of the Euclid survey. Using 1000 Euclid-like cluster catalogues, we investigated the effect of systematic uncertainties on cluster summary statistics and their auto- and cross-covariance, and performed a likelihood analysis to evaluate their impact on cosmological constraints, with a focus on the matter density parameter, $Ω_{\rm m}$, and on the power spectrum amplitude, $σ_8$. Combining cluster clustering with number counts significantly improves cosmological constraints, with the figure of merit increasing by over 300 % compared to number counts alone. We confirm that the two probes are uncorrelated, and the cosmological constraints derived from their combination are almost insensitive to the cosmology dependence of the covariance. We find that photometric redshift uncertainties broaden cosmological posteriors by 20--30 %, while secondary effects such as redshift-space distortions (RSDs) have a smaller impact on the posteriors -- 5 % for clustering alone, 10 % when combining probes -- but can significantly bias the constraints if neglected. We show that clustering data below $60\,h^{-1}\,$Mpc provides additional constraining power, while scales larger than the acoustic oscillation scale add almost no information on $Ω_{\rm m}$ and $σ_8$ parameters. The RSDs and photo-$z$ uncertainties also influence the number count covariance, with a significant impact of about 15--20 % on the parameter constraints.

astro-ph.CO↗
arXiv2026

Euclid. Predicting scaling relations for emission-line galaxies using simulated data

The Euclid spectroscopic surveys will substantially increase the number of observed emission-line galaxies. We assess the ability of the Euclid Wide Survey (EWS) and Euclid Deep Survey (EDS), at the final DR3 depth, to recover the star-forming main sequence (MS), dust-mass relation (DMR), and mass-metallicity relation (MZR) from emission-line measurements. We use MAMBO (mocks with abundance matching in Bologna) spectroscopic simulations processed with the official Euclid pipelines. The MS is traced over $0\leq z\leq 4$ using Pa$β$, H$α$, and [OII] as SFR tracers. The shallow EWS flux limit biases the MS towards higher normalisation and a flatter slope by selecting the brightest, most strongly star-forming galaxies. The deeper EDS enables almost complete sampling with Pa$β$ and H$α$ at log$_{10}(M_*/M_\odot)\geq10.3$ over $0\leq z\leq 1.88$, with mild biases at both redshift limits. The [OII]-based MS is increasingly biased towards higher SFRs at the highest redshifts. The DMR is traced through the Balmer decrement over $1.45\leq z\leq 1.88$ and $0.9\leq z\leq 1.88$ in the EWS and EDS, respectively. The derived colour excess agree well with the input values, although detecting the faint H$β$ line restricts the sample to less obscured galaxies at fixed $M_*$, particularly in the EWS; the DMR is better sampled in the EDS. Finally, a golden sample detected in multiple optical rest-frame emission lines at $1.49\leq z\leq 1.88$ recovers gas-phase metallicities with typical accuracy of 0.1 dex at log$_{10}(M_*/M_\odot)\geq10$, while lower-mass galaxies show biases up to 0.15 dex. Relative to H-band limited sample, this sample preferentially traces the upper MS and lower MZR. Despite the simplified simulations lacking effects such as mutual spectral contamination and detector persistence, these forecasts provide a benchmark for future Euclid spectroscopic analyses.

astro-ph.GA↗
arXiv2026

Euclid: Forecasting the number counts of bright line emitters in the Euclid Wide Survey and Euclid Deep fields

The Euclid mission will revolutionize our understanding of the visible Universe by collecting images and spectra of millions of galaxies across cosmic time and environments. Here, we forecast the number counts of galaxies emitting [OII], H\b{eta}, [OIII], Hα and Pa\b{eta} lines in the Euclid Wide Survey (EWS) and Deep Survey (EDS). We compare predictions from different models, including semi-analytic models and empirical scaling relations. We then simulate spectra for galaxies in the MAMBO lightcone using FastSpec, designed to rapidly generate one-dimensional spectra as observed by Euclid. We process these simulated spectra with the official Euclid spectroscopic pipeline to recover redshifts and line fluxes and derive expected counts. Predictions for Hα+[NII] emitters are broadly consistent across mocks and with existing observations. In the EWS, relative RMS scatter among mock predictions for integrated counts is approximately 19% for Hα+[NII], 44% for [OII] and 41% for [OIII], reflecting greater model dependence for oxygen-line forecasts. After accounting for flux losses and redshift misidentification, corrected flux measurements recover most intrinsic line counts, especially in the EDS. From the MAMBO-based FastSpec simulations, we predict that Euclid will detect about 42 million Hα emitters in the EWS and 1.7 million in the EDS. The same simulations predict approximately 0.5 and 0.8 million [OII] and [OIII] emitters, respectively, in the EDS, and about 1.3 and 7.5 million in the EWS. These non-Hα forecasts remain subject to substantial model-dependent uncertainties, as shown by scatter among the different mocks. These samples will be instrumental in pushing large-scale structure and baryon acoustic oscillation studies beyond redshift z~2, extending Euclid cosmological and galaxy evolution studies beyond what is achievable with Hα alone.

astro-ph.GA↗
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↗