arXiv subjects

T. Ribeiro

Publications and source records attributed to T. Ribeiro.

At least 19 recordsLinked to original sources

arXiv2026

Homogeneity scale in the local Universe: Model-independent estimate from S-PLUS iDR6 blue galaxies

We present a model-independent estimate of the angular homogeneity scale in the local Universe by analysing data from the Southern Photometric Local Universe Survey (S-PLUS). Two complementary estimators are employed: (i) a parametric approach fitting the power-law of the two-point angular correlation function, which yields the homogeneity scale $θ_H = 8.94_{-3.38}^{+1.20}\;{\rm deg}$; and (ii) a nonparametric fractal correlation dimension method, computing $\mathcal{D}_2(θ)$ directly from the correlation function, which results in $θ_H = 7.91_{-2.94}^{+5.50}\;{\rm deg}$. We apply both methodologies to a set of mock catalogs, generated with the Generator for Large Scale Structure algorithm, and find that both estimates are well within $1 σ$ of their respective median values. The transition scale to homogeneity, according to the $Λ$ cold dark matter (CDM) model, is defined for matter, i.e., $b = 1$. Measurements of this scale with observational data clearly depend on the cosmic tracer analyzed, and a calibration is necessary. Our study with blue galaxies, with bias $b \simeq 1$, provides a suitable estimate for comparison. Indeed, the results obtained in both approaches are compared with the value expected in the $Λ$CDM model, obtaining a good concordance.

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arXiv2026

CLAS+: A large catalog of Changing-Look AGN candidates selected through S-PLUS narrow-band photometry

Changing-look active galactic nuclei (CLAGN) exhibit rapid spectral transitions on timescales of months to years, challenging standard AGN unification models and providing unique insight into accretion-disk variability and obscuration processes. Despite their scientific importance, systematic searches for CLAGN remain limited by the scarcity of multi-epoch spectroscopy and the difficulty of constructing large samples efficiently. We introduce CLAS+, a catalog constructed by comparing synthetic photometry derived from DESI DR1 and SDSS DR17 spectra with contemporaneous narrow-band imaging from the S-PLUS survey. Applying our pipeline to a parent sample of 98,139 quasars, we select high-confidence CLAGN candidates above a threshold of reduced chi-squared $χ_r^2 > 15$. We identify 3,554 strong CLAGN candidates, corresponding to 3.6\% of the parent sample. This selected fraction is conditional on the adopted criterion and should not be interpreted as an intrinsic CLAGN occurrence rate. Cross-matching with existing CLAGN compilations shows that CLAS+ identifies a large population of previously unreported high-priority candidates (3,481). Among the spectroscopic--photometric comparisons with reliable temporal classification, 40\% are classified as photometric turn-on, 41\% as intermediate, and 19\% as turn-off. We also find an apparent redshift dependence in the relative fractions, with photometric turn-on candidates becoming more common at higher redshifts within the CLAS+ selected sample. Therefore, narrow-band photometry provides a powerful and efficient alternative to purely spectroscopic searches for identifying CLAGN candidates at scale. CLAS+ substantially expands the known CLAGN candidate population and provides a valuable target list for future spectroscopic follow-up and time-domain studies with facilities such as Rubin/LSST.

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arXiv2026

S-PLUS Clusters And Large-scale Environments (SCALE): I. A catalog of known clusters and groups in DR5 and a pilot study of Abell 4038

Within the framework of the Southern Photometric Local Universe Survey (S-PLUS), we introduce ${\bf S}$-PLUS ${\bf C}$lusters ${\bf A}$nd ${\bf L}$arge-scale ${\bf E}$nvironments (SCALE), a project dedicated to the study of galaxy clusters, groups, and their environments using 12-band photometry of S-PLUS combined with spectroscopic and photometric data from the literature. In this first paper, we present a catalog of 83 previously known systems in the redshift range $0.008 \leq z_{\rm spec} \leq 0.1$, for which we derive $R_{200}$, $M_{200}$, and velocity dispersions. Spectroscopic members are selected and matched with S-PLUS photometric redshifts (photo-$z$s). We find very good agreement between literature spectroscopic redshifts (spec-$z$s) and S-PLUS photometric redshifts (photo-$z$s), demonstrating the potential of the latter for cluster and group membership determination. As a proof of concept, we obtain photometric memberships for Abell 4038 using the Reliable Photometric Membership technique. A two- and three-dimensional analysis of the region within $10 h^{-1}$ Mpc ($10\times R_{200}$) from the center of Abell 4038 reveals about a dozen substructures including two additional clusters within $1.3\times R_{200}$ (Abell 4038B and Abell 4049). A color-luminosity segregation analysis shows that more luminous (less luminous) galaxies are redder (bluer), as expected. Low-concentration galaxies ($C \leq 2.5$) exhibit a weaker color-luminosity dependence, compared to higher-concentration ones, indicating mass-dependent evolutionary pathways that challenge a simple morphology-color dichotomy, with low-luminosity galaxies presenting bluer colors largely independent of concentration. The SCALE catalog provides a valuable basis for future studies of large-scale structures and their connection to galaxy evolution.

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arXiv2026

S-PLUS Clusters And Large-scale Environments (SCALE): II. PZWav versus redMaPPer identification of eRosita groups

We present the construction and characterization of a multi-wavelength catalog of galaxy groups and clusters by matching optical detections from the Southern Photometric Local Universe Survey (S-PLUS) with extended X-ray emission from the first eROSITA all-sky survey data release (eRASS1). We employ a probabilistic matching framework, based on the modified Hausdorff distance, to associate galaxy systems identified by the PZWav cluster finder and characterized by the AME membership estimator with X-ray surface brightness contours. This method explicitly accounts for the photometric redshift probability distribution of galaxies and allows us to explore the critical trade-off between catalog completeness and purity. We investigate how the matched sample changes with different optical selection depths, defined by absolute magnitude cuts of $M_r$ < -18.5, -19, -19.5, and -20 sampling redshifts within 0.08 < z < 0.25, and across purity levels of 80%, 90%, and 95%. We find that fainter optical cuts enhance the recovery of low-mass, low-luminosity groups, while brighter cuts favor more massive clusters and increase the effective survey volume at higher redshifts. Stricter purity requirements reduce contamination but systematically lower completeness, particularly for low-luminosity systems. The derived X-ray luminosity functions agree well with previous determinations, and the logN-logS distributions confirm the high recovery rate of luminous clusters. Comparisons with the redMaPPer cluster catalog validate our approach, showing consistent trends and significant overlap, while our method offers improved completeness at the group scale. This work demonstrates a robust, flexible methodology for creating reliable multi-wavelength cluster catalogs, essential for cosmological studies and investigations of galaxy evolution in dense environments.

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arXiv2026

The S-PLUS Fornax Project (S+FP): Fornax-like clusters in cosmological hydrodynamical simulations

The Fornax galaxy cluster constitutes a suitable laboratory to explore the evolution of galaxies in a dense environment. Recently, the Southern Photometric Local Universe Survey (S-PLUS) has obtained unprecedented photometric information of Fornax, revealing new features regarding its galaxy populations and surrounding regions. In this context, simulations are invaluable tools to interpret the past, present and fate of such observational findings. We aim to deliver a robust photometric catalog of simulated Fornax-like systems in cosmological context, to consistently contrast them with S-PLUS data. We analyze Fornax analogs from the EAGLE and IllustrisTNG simulations, selected using observed properties of the Fornax cluster and its central galaxy NGC 1399. For each system, we generated synthetic photometry in the 12 S-PLUS bands using the SKIRT radiative transfer code, reproducing the instrumental configuration of the S-PLUS survey. Simulated data cubes, mock images, spectral energy distributions, magnitudes and colors were obtained for each galaxy in our selected simulated Fornax analogs. The synthetic photometry and spectra derived from simulations show a good agreement with the S-PLUS observations. We identify particular systems which show some similarity with the spatial distribution of galaxies in Fornax. Such simulated candidates reproduce the observed color-magnitude relation and the spatial substructure between the cluster core and the Fornax A region. Also, simulated galaxies are bluer at higher cluster-centric distances, in agreement with observations. Although modest discrepancies were obtained between the observed and simulated color-magnitude diagrams in some cases, our results support the suitability of our selection criteria and synthetic photometry, and the reliability of current cosmological simulations to reproduce key general features of the Fornax cluster.

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arXiv2026

Searching for Binary Black Hole Merger Emission in AGN Disks: Optical and Spectroscopic Follow-up of S240413p

The conditions under which binary black hole (BBH) mergers embedded in active galactic nucleus (AGN) disks produce detectable optical counterparts remain poorly constrained observationally. We report multi-epoch optical imaging and spectroscopic follow-up of S240413p, an O4 BBH candidate with 98\% classification confidence, obtained with the T80-South telescope through the S-PLUS Transient Extension Program (STEP). Our observations cover the 99\% credible region across epochs that span $\sim$300 days post-merger. We prioritize AGN-hosted environments and identify two transient candidates, STEP2024gab/ZTF18acvgziq and STEP2024phe/ZTF19aaflhnr. SOAR/Goodman spectroscopy and archival DESI spectra yield host supermassive black hole masses of $\log M_\mathrm{SMBH}/\mathrm{M}_\odot = 7.15 \pm 0.05$ and $8.02 \pm 0.04$. We compute predicted flare delay distributions for each host using a thermal radiation-driven outflow emission model and the spectroscopically derived host properties. Migration traps produced by thermal torques occur at $R_\text{BH}/R_g \approx 10^{4.2}$ and $10^{3.4}$ for the two hosts, with predicted flare delays spanning tens to several hundred days; our late epoch at $\sim$ 300 days coincides with both the peak of these distributions and the migration trap locations, while early epochs overlap only their tails. We find no confirmed counterpart; a seasonal visibility gap leaves open the possibility that a flare occurred undetected, the merger may not have occurred within the AGN disk itself, or any emission may have been obscured by intrinsic AGN variability. These results demonstrate that long-baseline, AGN-prioritized monitoring is a necessary condition for accessing the highest probability region of BBH merger parameter space, and establish the need for physically informed follow-up strategies in the Rubin/LSST era.

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arXiv2026

S-PLUS: Beyond Spectroscopy IV. Stellar Parameters and Elemental-abundance Ratios for Six Million Stars from DR4 and First Results for the Magellanic Clouds

We combine narrow/medium-band filter photometry from the Southern Photometric Local Universe Survey (S-PLUS) DR4 with ultra broad-band filter photometry from Gaia EDR3 to derive fundamental stellar parameters ($T_{\rm eff}$, $\log g$, [Fe/H], ages) and elemental-abundance ratios ([C/Fe] and [$α$/Fe]) for 5.4 million stars in the Galaxy (4.9 million dwarfs and 0.5 million giants), as well as for over 0.7 million red giant stars in the Large and Small Magellanic Clouds (LMC and SMC). The precisions of the abundance estimates range from 0.05-0.10 dex for metallicity in the relatively metal-rich range ([Fe/H] $> -1.0$) to 0.10-0.30 dex in the metal-poor regime ([Fe/H] $<-1.0$), 0.10-0.20\,dex for [C/Fe], and 0.05 dex for [$α$/Fe]. The stellar parameters for LMC and SMC member stars are somewhat less precise than those from the S-PLUS main survey, primarily because of the effect of high reddening. The use of both metallicity- and carbon-sensitive filters provides unbiased measurements of both [Fe/H] and [C/Fe], of particular importance for very low-metallicity ([Fe/H] $< -2.0$) stars, where carbon enhancement can lead to systematically high estimates of [Fe/H] when only a single metallicity-sensitive filter is employed. Furthermore, multiple narrow-band filters enable metallicity estimates down to [Fe/H] $\sim -4.0$ with an accuracy of around 0.3 dex, exceeding the precision typically achieved by low/medium-resolution spectroscopy. This extensive photometric dataset, combined with the other three datasets in this series, will serve as a valuable legacy resource for Milky Way and Magellanic Clouds studies.

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arXiv2026

The S-PLUS Fornax Project (S+FP): An extragalactic catalog covering $\sim$ 5 virial radii around NGC 1399 with galaxy properties

Observational extragalactic catalogs over wide sky areas are essential for uncovering the large-scale structure of the Universe. They allow, among others, cosmological studies and density analyses that impose strong constraints on models of galaxy formation and evolution. By taking advantage of the wide field images and the 12 optical bands of the Southern Photometric Local Universe Survey (S-PLUS), we aim at providing a catalog of galaxies located, in projection, towards the Fornax galaxy cluster, within $\sim$ 5 virial radii in right ascension (R.A.) and $\sim$ 3 virial radius in declination (Dec) around NGC,1399, the dominant galaxy of the cluster. Such a catalog will allow unprecedented large-scale structure studies in that sky region. Supervised deep learning algorithms have been developed, utilizing neural networks complemented with dimensionality reduction techniques, to classify and separate spurious objects, stars and galaxies in a photometric catalog previously built for the S-PLUS Fornax Project (S+FP). That catalog was built using a combination of SExtractor configurations optimized for galaxy detection and characterization. A catalog of 119,580 galaxies was obtained in the direction of the Fornax cluster containing photometric information in the 12 optical bands of S-PLUS complemented with GALEX (UV), VHS-VISTA (NIR) and AllWISE (MIR) data. We estimate photometric redshifts (σ_ NMAD $\sim$ 0.0219) with a lower limit of z_ lim $\sim$ 0.03. Stellar masses, star formation rates (SFRs) and D4000_N index estimates were obtained through a machine learning approach, by matching S-PLUS photometric data to SDSS spectroscopic data. The completeness of the catalog (72%) was calculated by comparing with mock catalogs ...

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arXiv2025

Targeting cluster galaxies for the 4MOST CHANCES Low-z sub-survey with photometric redshifts

The evolution of galaxies is shaped by both internal processes and their external environments. Galaxy clusters and their surroundings provide ideal laboratories to study these effects, particularly mechanisms such as quenching and morphological transformation. The Chilean Cluster galaxy Evolution Survey (CHANCES) Low-z sub-survey is part of the CHileAN Cluster galaxy Evolution Survey, a 4MOST community survey designed to uncover the relationship between the formation and evolution of galaxies and hierarchical structure formation as it happens, through deep and wide multi-object spectroscopy. We present the target selection strategy followed to select galaxy cluster candidate members for the CHANCES low-z sub-survey, in and around 50 clusters and two superclusters at z<0.07, out to (5XR200) and down to mr= 20.4. Combining public photometric redshift estimates from the DESI Legacy Imaging Survey and T80S/S-PLUS iDR5, with custom photometric redshifts, we identify likely galaxy cluster candidate members whose photometric redshifts are consistent with being at the known redshift of the cluster and measure the average deviations of their photometric redshifts with respect to the spectroscopic redshift measurements σNMAD. We have successfully compiled our CHANCES-low-redshift catalogues, split into three different sub-surveys: low-z bright (mr<18.5), low-z faint (18.5<=mr<20.4) and low-z faint supplementary, by selecting>= 500,000 galaxy cluster candidate members and including confirmed spectroscopic galaxy cluster members, from which we expect to obtain 4MOST low-resolution (R~6500) spectra for ~320,000 galaxies. The CHANCES Low-z target catalogues form a statistically robust sample for spectroscopic follow-up, allowing studies of galaxy evolution and environmental effects in nearby cluster and supercluster environments.

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arXiv2025

The Southern Photometrical Local Universe Survey (S-PLUS): searching for metal-poor dwarf galaxies

The metal content of a galaxy's interstellar medium reflects the interplay between different evolutionary processes such as feedback from massive stars and the accretion of gas from the intergalactic medium. Despite the expected abundance of low-luminosity galaxies, the low-mass and low-metallicity regime remains relatively understudied. Since the properties of their interstellar medium resemble those of early galaxies, identifying such objects in the Local Universe is crucial to understand the early stages of galaxy evolution. We used the DR3 catalog of the Southern Photometric Local Universe Survey (S-PLUS) to select low-metallicity dwarf galaxy candidates based on color selection criteria typical of metal-poor, star-forming, low-mass systems. The final sample contains approximately 50 candidates. Spectral energy distribution fitting of the 12 S-PLUS bands reveals that $\sim$ 60% of the candidates are best fit by models with low stellar metallicities. We obtained long-slit observations with the Gemini Multi-Object Spectrograph to follow-up a pilot sample and confirm whether these galaxies have low metallicities. We find oxygen abundances in the range $7.28<$ 12 + log(O/H) $< 7.82$ (4% to 13% of the solar value), confirming their metal-poor nature. Most targets are outliers in the mass-metallicity relation, i.e. they display a low metal content relative to their observed stellar masses. In some cases, perturbed optical morphologies might give evidence of dwarf-dwarf interactions or mergers. These results suggest that the low oxygen abundances may be associated with an external event causing the accretion of metal-poor gas, which dilutes the oxygen abundance in these systems.

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arXiv2025

A cosmology weakly dependent measurement of 2D Baryon Acoustic Oscillations scale from the Southern Photometric Local Universe Survey

Baryon Acoustic Oscillations (BAO) provide a robust standard ruler for observational cosmology, enabling precise constraints on the expansion history of the Universe. We present a weakly model-dependent measurement of the BAO angular scale in the low-redshift Universe using the blue galaxies from the Southern Photometric Local Universe Survey (S-PLUS). Our analysis is based on the 2-point angular correlation function applied to a selected photometric sample of $5977$ galaxies with redshifts $0.03 \leq z \leq 0.1$. To account for photometric redshift uncertainties, we implement a resampling technique using the probability distribution function of each galaxy. Angular correlations are computed using the Landy-Szalay estimator; the uncertainties are quantified using a set of $1000$ log-normal mock catalogues. Our 2-point angular correlation analyses reveal a prominent BAO signal that after a shift correction, due to the projection effect caused by the finite thickness of the redshift bin, provides the transversal BAO measurement: $θ_{BAO} = 21.81^{\circ} \pm 0.85^{\circ}$, at $z_{eff} = 0.075$, detected with a statistical significance of $3.22 σ$. In addition, we performed consistency tests that support the robustness of our result. Our measurement constitutes the first robust detection of the transversal BAO scale: at the lowest-redshift in the Universe and using multi-band (narrow+wide) photometry data from the S-PLUS.

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arXiv2025

Long-Term Optical Follow Up of S231206cc: Multi-Model Constraints on BBH Merger Emission in AGN Disks

The majority of gravitational wave events detected by the LIGO, Virgo, and KAGRA Collaboration originate from binary black hole (BBH) mergers, for which no confirmed electromagnetic counterparts have been identified to date. However, if such mergers occur within the disk of an active galactic nucleus (AGN), they may generate observable optical flares induced by relativistic jet activity and shock-heated gas. We present results from a long-term optical follow-up of the gravitational wave event S231206cc, conducted with the T80-South telescope as part of the S-PLUS Transient Extension Program (STEP). Our search prioritized AGN-hosted environments by crossmatching the gravitational wave localization with known AGN catalogs. No candidate met the criteria for a viable optical counterpart. We explored three BBH merger scenarios predicting optical emission in AGN disks: (i) ram pressure stripping, (ii) long-term emission from an emerging jet cocoon, and (iii) jet breakout followed by shock cooling. Using our observational cadence and depth, we constrained the BBH parameter space, including the remnant's location within the AGN disk, kick velocity, and supermassive black hole (SMBH) mass. Detectable flares are most likely when mergers occur at 0.01-0.1 parsecs from SMBHs with masses between 10^7 and 10^8 solar masses, where short delay times and long durations best align with our follow-up strategy. These results provide a framework for identifying AGN-hosted BBH counterparts and guiding future multimessenger efforts.

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arXiv2025

The S-PLUS Fornax Project (S+FP): Mapping H$α$+[NII] emission in 77 Fornax galaxy members reaching $\sim$4 Rvir

The Fornax cluster, the second-largest galaxy cluster within 20 Mpc, presents an ideal environment for studying environmental effects on galaxy evolution. Utilizing data from the Southern Photometric Local Universe Survey (S-PLUS), this study explores the H$α$+[NII] emission maps across an area of approximately 208 square degrees around NGC 1399. For such, a dedicated semi-automated pipeline, Pixel-to-Pixel Emission Line Estimate (PELE), was developed to generate emission line maps by processing S-PLUS images using the Three Filter Method. A morphological analysis was conducted using the ASTROMORPHLIB package to determine whether H$α$+[NII] emitters exhibit perturbed features. The study successfully detected 77 H$α$+[NII] emitters with $r<18$ mag, extending to four times the virial radius of the Fornax cluster. PELE demonstrated its ability to recover flux down to 2e-17 erg s$^{-1}$ cm$^{-2}$ when compared to H$α$ maps from MUSE/VLT. Among the emitters, 25% are early-type galaxies (ETG) and 75% late-type galaxies (LTG). Signs of morphological perturbation or merger activity are observed in 44% of the LTG and in three ETG located beyond the cluster's virial radius. A significant fraction (91%) of the emitters are identified as recent infallers, primarily located in the northwestern region of the cluster, while others are associated with the infalling group Fornax A in the southwest. Disturbed, low-mass galaxies at larger cluster-centric distances provide evidence of galaxies begin transforming before entering the main cluster. This study demonstrates S-PLUS's effectiveness in detecting emitters, whose distribution reflects the Fornax cluster's assembly history, with LTG linked to recent infall from the field, possibly along a Fornax-Eridanus filament, and ETG may have evolved prior to entry.

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arXiv2025

An Unsupervised Machine Learning Approach to Identify Spectral Energy Distribution Outliers: Application to the S-PLUS DR4 data

Identification of specific stellar populations using photometry for spectroscopic follow-up is a first step to confirm and better understand their nature. In this context, we present an unsupervised machine learning approach to identify candidates for spectroscopic follow-up using data from the Southern Photometric Local Universe Survey (S-PLUS). First, using an anomaly detection technique based on an autoencoder model, we select a large sample of objects ($\sim 19,000$) whose Spectral Energy Distribution (SED) is not well reconstructed by the model after training it on a well-behaved star sample. Then, we apply the t-distributed Stochastic Neighbor Embedding (t-SNE) algorithm to the 66 color measurements from S-PLUS, complemented by information from the SIMBAD database, to identify stellar populations. Our analysis reveals 69 carbon-rich star candidates that, based on their spatial and kinematic characteristics, may belong to the CH or Carbon-Enhanced Metal-Poor (CEMP) categories. Among these chemically peculiar candidates, we identify four as likely carbon dwarf stars. We show that it is feasible to identify three primary white dwarf (WD) populations: WDs with hydrogen-dominated atmospheres (DA), WDs with neutral helium-dominated atmospheres (DB), and the WDs main sequence binaries (WD + MS). Furthermore, by using eROSITA X-ray data, we also highlight the identification of candidates for very active low-mass stars. Finally, we identified a large number of binary systems using the autoencoder model, but did not observe a clear association between the overdensities in the t-SNE map and their orbital properties.

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arXiv2025

The S-PLUS Fornax Project (S+FP): Mapping globular clusters systems within 5 virial radii around NGC 1399

We present the largest sample ($\sim$13,000 candidates, $\sim$3000 of wich are bona-fide candidates) of globular cluster (GCs) candidates reported in the Fornax Cluster so far. The survey is centered on the NGC 1399 galaxy, extending out to 5 virial radii (\rv) of the cluster. We carried out a photometric study using images observed in the 12-bands system of the Southern Photometric Local Universe Survey (S-PLUS), corresponding to 106 pointings, covering a sky area of $\sim$208 square degrees. Studying the properties of spectroscopically confirmed GCs, we have designed a method to select GC candidates using structural and photometric parameters. We found evidence of color bimodality in 2 broad bands colors, namely $(g-i)_{0}$ and $(g-z)_{0}$, while, in the narrow bands, we did not find strong statistical evidence to confirm bimodality in any color. We analyzed the GCs luminosity functions (GCLF) in the 12-bands of S-PLUS, and we can highlight two points: a) due to the relatively shallow depth of S-PLUS, it is only possible to observe the bright end of the GCLF and, b) at that level, in all the bands it can be appreciated the log-normal distribution typical for GC systems. With the spatial coverage reached in this study, we are able for the first time explore the large scale distribution of GCs within and around a galaxy cluster. In particular, we noted that the GCs might be clustered along substructures, which traces the current cluster build up.

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arXiv2025

Mapping H$α$-Excess Candidate Point Sources in the Southern Hemisphere Using S-PLUS Data

Context. We use the Southern Photometric Local Universe Survey (S-PLUS) Fourth Data Release (DR4) to identify and classify H$α$-excess point sources in the Southern Sky, combining photometric data from 12 S-PLUS filters with machine learning to improve classification of H$α$-related phenomena. Aims. Our goal is to classify H$α$-excess point sources by distinguishing Galactic and extragalactic objects, particularly those with redshifted emission lines, and identifying variability phenomena like RR Lyrae stars. Methods. We selected H$α$-excess candidates using the ($r - J0660$) vs. ($r - i$) colour-colour diagram from the S-PLUS main survey (MS) and Galactic Disk Survey (GDS). UMAP for dimensionality reduction and HDBSCAN clustering were used to separate source types. Infrared data was incorporated, and a Random Forest model was trained on clustering results to identify key colour features. New colour-colour diagrams from S-PLUS MS and infrared data offer a preliminary classification. Results. Combining multiwavelength data with machine learning significantly improved H$α$-excess source classification. We identified 6956 sources with excess in the $J0660$ filter. Cross-matching with SIMBAD explored object types, including emission-line stars, young stellar objects, nebulae, stellar binaries, cataclysmic variables, QSOs, AGNs, and galaxies. Using S-PLUS colours and machine learning, we separated RR Lyrae stars from other sources. The separation of Galactic and extragalactic sources was clearer, but distinguishing cataclysmic variables from QSOs at certain redshifts remained challenging. Infrared data refined the classification, and the Random Forest model highlighted key colour features for future follow-up spectroscopy.

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arXiv2024

The Quasar Catalogue for S-PLUS DR4 (QuCatS) and the estimation of photometric redshifts

The advent of massive broad-band photometric surveys enabled photometric redshift estimates for unprecedented numbers of galaxies and quasars. These estimates can be improved using better algorithms or by obtaining complementary data such as narrow-band photometry, and broad-band photometry over an extended wavelength range. We investigate the impact of both approaches on photometric redshifts for quasars using data from Southern Photometric Local Universe Survey (S-PLUS) DR4, Galaxy Evolution Explorer (GALEX) DR6/7, and the unWISE catalog for the Wide-field Infrared Survey Explorer (WISE) in three machine learning methods: Random Forest, Flexible Conditional Density Estimation (FlexCoDE), and Bayesian Mixture Density Network (BMDN). Including narrow-band photometry improves the root-mean-square error by 11% in comparison to a model trained with only broad-band photometry. Narrow-band information only provided an improvement of 3.8% when GALEX and WISE colours were included. Thus narrow bands play a more important role for objects that do not have GALEX or WISE counterparts, which respectively makes 92% and 25% of S-PLUS data considered here. Nevertheless, the inclusion of narrow-band information provided better estimates of the probability density functions obtained with FlexCoDE and BMDN. We publicly release a value-added catalogue of photometrically selected quasars with the photo-z predictions from all methods studied here. The catalogue provided with this work covers the S-PLUS DR4 area (~3000deg$^2$), containing 645 980, 244 912, 144 991 sources with the probability of being a quasar higher than, 80%, 90%, 95% up to r < 21.3 and good photometry quality in the detection image. More quasar candidates can be retrieved from the S-PLUS data base by considering less restrictive selection criteria.

astro-ph.CO↗

arXiv2024

The S-PLUS Fornax Project (S+FP): SExtractor detection and measurement of nearby galaxies in large photometric surveys

All-sky multi-band photometric surveys represent a unique opportunity of exploring rich nearby galaxy clusters up to several virial radii, reaching the filament regions where pre-processing is expected to occur. These projects aim to tackle a large number of astrophysical topics, encompassing both the galactic and extragalactic fields. In that sense, generating large catalogues with homogeneous photometry for both resolved and unresolved sources that might be interesting to achieve specific goals, imposes a compromise when choosing the set of parameters to automatically detect and measure such a plethora of objects. In this work we present the acquired experience on studying the galaxy content of the Fornax cluster using large catalogues obtained by the Southern Photometric Local Universe Survey (S-PLUS). We realized that some Fornax bright galaxies are missed in the S-PLUS iDR4 catalogues. In addition, Fornax star-forming galaxies are included as multiple detections due to over-deblending. To solve those issues, we performed specific SExtractor runs to identify the proper set of parameters to recover as many Fornax galaxies as possible with confident photometry and avoiding duplications. From that process, we obtained new catalogs containing 12-band improved photometry for ~ 3 x 10^6 resolved and unresolved sources in an area of ~ 208 deg2 in the direction of the Fornax cluster. Together with identifying the main difficulties to carry out the study of nearby groups and clusters of galaxies using S-PLUS catalogs, we also share possible solutions to face issues that seem to be common to other ongoing photometric surveys.

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