Ana Laura O’mIll

Aims . Leveraging the high-precision photometric redshifts of the Physics of the Accelerating Universe Survey (PAUS), we aim to investigate the connection between active galactic nuclei (AGNs) and galaxy pairs up to redshifts of ∼1.0. Methods . We identified 16 824 galaxy pairs with projected separations of r _p < 100 kpc and radial-velocity differences of ∆ V < 3500 km s ⁻¹ . AGNs were selected by cross-matching PAUS galaxies with multi-wavelength AGN catalogues, yielding 270 AGNs in pairs out of a parent sample of 8880 AGNs in PAUS. We constructed control samples of isolated AGNs; non-AGNs in pairs; and isolated non-AGNs matched in redshift, absolute magnitude, and environment. Results . Active galactic nuclei in pairs show progressively redder rest-frame colours with increasing redshift, particularly at redshifts of z ≳ 0.5, whereas isolated AGNs and non-AGNs in pairs show no significant colour evolution and remain at M _g − M _r ∼ 0.65. Pairs hosting AGNs are also preferentially morphologically disturbed interacting systems found at smaller projected separations and velocity offsets, consistent with more dynamically advanced interactions. Conclusions . These results provide evidence of a redshift-dependent link between galaxy interactions and AGN activity, suggesting that interactions play an increasingly important role in triggering nuclear activity at intermediate redshifts. This study highlights the unique capability of PAUS to probe AGN–galaxy interaction connections beyond the local Universe with unprecedented statistical power.

Compact groups (CGs) of galaxies are dense systems where projected separations are comparable to their optical diameters. A subset—non-isolated CGs—are embedded within major structures. Using multiband S-PLUS data, we analyse galaxies in 122 non-isolated CGs within more-massive systems, such as larger groups and clusters. We compare them to galaxies in the host structures, hereafter surrounding group galaxies. Structural parameters were obtained with MorphoPLUS, a pipeline for multiwavelength Sérsic profile fitting. Dividing galaxies into early-type galaxies (ETGs), transition, or late-types (LTGs), we find the following: (1) Non-isolated CGs host higher quenched fractions and more ETGs, especially for stellar masses log ( M / M ⊙ ) > 10.2 than surrounding groups. (2) Sérsic indices increase with wavelength for all morphological types in both environments, whereas effective radii show a stronger morphology-dependent behavior—ETGs become more compact towards redder bands, while LTGs exhibit flatter Re ( λ ) trends. Environmental differences remain weak, with only a modest enhancement of the gradients for ETGs in non-isolated CGs. (3) Transition galaxies in CGs show a concentrated R _e – n distribution and faint-end bimodality, consistent with ongoing morphological transformation absent in surrounding groups. (4) Phase-space analysis indicates that some CGs in clusters are projection artifacts, while others are genuine dense systems at various infall stages, from recent arrivals to ancient remnants. These results show that galaxies in non-isolated CGs follow distinct evolutionary paths compared to their surrounding groups galaxies, suggesting that the compact configuration plays a unique role beyond the influence of the larger-scale environment.

Aims. We investigate if systems of multiple Lyman-alpha emitters (LAEs) can serve as a proxy for dark matter halo mass, assess how their radiative properties relate to the underlying halo conditions, and explore the physics of star formation activity in LAEs and its relation to possible physically related companions. Methods. We used data from the One-hundred-deg ² DECam Imaging in Narrowbands (ODIN) survey, which targets LAEs in three narrow redshift slices. We identified physically associated LAE multiples in the COSMOS field at z = 2.4, z = 3.1, and z = 4.5, and we used a mock catalog from the IllustrisTNG100 simulation to assess the completeness and contamination affecting the resulting sample of LAE multiples. We then studied their statistical and radiative properties as a function of multiplicity, for which we adopted the term “multiplicity” to refer to the number of physically associated LAEs. Results. We find a strong correlation between LAE multiplicity and host halo mass in the mocks, with higher multiplicity systems preferentially occupying more massive halos. In both the ODIN and the mock sample, we find indications that the mean Ly α luminosity and UV magnitude of LAEs in multiples increase with multiplicity. The halo-wide LAE surface brightness densities in Ly α and UV increase with multiplicity, reflecting more compact and actively star-forming environments. The close agreement between the model and ODIN-COSMOS observations supports the validity of the Ly α emission model in capturing key physical processes in LAE environments. Finally, a subhalo-based perturbation-induced star formation model reproduces the minimum subhalo mass distribution in simulations at z = 2.4, suggesting that local perturbations–rather than the presence of LAE companions–drive star formation activity in these systems. For the higher redshift samples, neighbor perturbations do not seem to be the main driver that triggers star formation.

Context. The Circinus galaxy is the nearest type-2 Seyfert galaxy, located at a distance of 4.2 Mpc. Its environment is challenging to explore because of the low Galactic latitudes of its location, behind the disc of the Milky Way. Aims. The long-term goal of this work is to characterise the Circinus galaxy halo. We are also interested in determining the possible presence of dwarf satellites using near-infrared (NIR) data. Methods. We selected 1542 galaxies from the VISTA Variables in the Vía Láctea (VVV) NIR galaxy catalogue within a 2-degree radius around the Circinus galaxy, representing roughly 2/3 of the virial radius. We used structural parameters, such as the half-light radii and colours, and correlations were examined. A neural network was trained with 486 galaxies with known spectroscopic redshifts to estimate photometric redshifts for all of these galaxies. The potential satellites of the Circinus galaxy were defined on the basis of half-light radii that were compatible with the typical sizes of dwarf satellites in galaxies and combined with photometric redshifts. Results. The galaxy properties have been reliably characterised down to K _s ∼ 15.5 mag, representing about 90% completeness of the detections. At the distance of the Circinus galaxy, this limiting magnitude corresponds to a K _s absolute magnitude of −12.6 mag, allowing us to locate dwarf galaxies. In total, there are 20 galaxies with half-light radii larger than 2.45 arcsec, but only 8 of them have photometric redshifts below 0.04. None of these galaxies are close to the Circinus galaxy, which has a redshift of 0.0015 and shows no evidence of associated clustering. The ANNz model exhibited a high degree of accuracy in the range of 0.001 < z _phot < 0.023, thereby validating this method in these extinct regions. Conclusions. The presence of dwarf satellites associated with the Circinus galaxy could not be confirmed with the available data in the studied region. The apparent lack of satellites could be genuine, possibly related to AGN feedback effects. Nevertheless, this work demonstrates the effectiveness of combining near-infrared data and machine learning techniques to estimate photometric redshifts at low Galactic latitudes, thereby providing useful information for future spectroscopic follow-up campaigns.

Context. Studies of large-scale structures in the Universe reveal that galaxy clusters form in regions of matter overdensity, at the intersection of the filamentary structures that comprise the cosmic web. In this process, satellite galaxies tend to spatially align with the major axis of the brightest cluster galaxy (BCG), a phenomenon influenced by both cluster-scale dynamics and the surrounding large-scale environment. Aims. In this study we investigated the alignment of satellite galaxies relative to the BCG position angle using photometric data from the fifth data release of the Southern Photometric Local Universe Survey (S-PLUS/DR5) to unveil how galaxies evolve under the influence of both local and global conditions. Methods. Using three complementary statistical tests, the Kuiper V, binomial, and Rao’s spacing tests, we explored how the alignment signal varies with BCG and cluster properties. Our sample includes 58 galaxy clusters with spectroscopically confirmed BCGs within the STRIPE-82 region, up to a redshift of z < 0.12. Results. The alignment strength is more pronounced for redder BCGs and brighter BCGs, with the most luminous BCGs presenting the strongest correlation with their satellite distributions. In addition, combining multiple properties, such as BCG colour and luminosity, does not further enhance the alignment signal, as the samples naturally favour BCGs with properties that maximise the effect. Beyond 3 R₂₀₀, satellite colours become more evolved along the BCG major axis for the reddest BCGs, suggesting preprocessing within large-scale filaments. These findings are further evidence of the role of cluster-scale dynamics and large-scale structure in shaping galaxy alignments.

Compact groups (CGs) of galaxies are an extreme environment for the morphological transformations and the cessation of star formation in galaxies. However, despite initially being conceived as isolated systems, it is now widely recognised that many of them are not as isolated as expected. Our objective is to understand the dynamics of CGs, as well as how the environment surrounding CGs impacts their morphological and physical properties. To achieve this, we selected a sample of 316 CGs in the Stripe 82 region, with a total of 1011 galaxies, and a sample of 2281 field galaxies as a control sample. We find that at least 41% of our sample of CGs are part of major structures, i.e. non-isolated CGs. We find a bimodality in the effective radius (R_e)-Sérsic index (n) plane for all transition galaxies (those with (u − r) > 2.3 and n < 2.5) in CGs. Additionally, transition galaxies in isolated CGs populate more densely the R_e − n plane for n < 1.75. In contrast, transition galaxies in non-isolated CGs show a bimodal distribution in the R_e − n plane, with the n values smoothly increasing towards higher values, and 62% of these galaxies having n > 1.5. This indicates that the majority of these galaxies have already undergone a morphological transformation and primarily contribute to the population of more compact galaxies in the R_e − n plane. We find that galaxies in our sample of CGs have a lower mean specific star formation rate (sSFR) compared to the control sample, with non-isolated CGs showing even lower sSFR values, indicating that dense environments suppress star formation. Additionally, non-isolated CGs have a higher fraction of quenched galaxies relative to isolated CGs and the control sample. Based on our results, we propose an evolutionary scenario where the major structures in which the CGs are embedded accelerate the morphological transformations of their galaxy members, and also facilitates preprocessing. Our findings highlight the importance of considering the larger structures in which CGs may be located, when analysing the properties of their galaxy members, as this can significantly affect the evolution of CGs and their galaxies.

We investigated the population of low-mass central galaxies with M_⋆ = 10^9.5 − 10¹⁰ h⁻¹ M_⊙, inhabiting regions near massive groups and clusters of galaxies using the IllustrisTNG300 and MDPL2-SAG simulations. We set out to study their evolutionary histories, aiming to find hints about the large-scale conformity signal they produce. We also used a control sample of central galaxies with the same stellar mass range located far away from massive structures. For both samples, we find a subpopulation of galaxies accreted by another halo in the past, but now considered central galaxies; we refer to these objects as former satellites. The number of former satellites is higher for quenched central galaxies near massive systems, with fractions of 45% and 17% in IllustrisTNG300 and MDPL2-SAG, respectively. The differences in the numerical resolution of each simulation lead to the different fractions of former satellites. Our results in TNG300 show that former satellites “pollute” the sample of central galaxies because they suffered environmental processes when they were satellites hosted typically by massive dark matter halos (M₂₀₀ ≥ 10¹³ h⁻¹ M_⊙) since z ≲ 0.5. After removing former satellites, the evolutionary trends for quenched central galaxies near massive structures are fairly similar to those of the quenched control galaxies, showing small differences at low redshift. For MDPL2-SAG instead, former satellites were hosted by less massive halos, with a mean halo mass around 10^11.4 h⁻¹ M_⊙, and the evolutionary trends remain equal before and after removing former satellite galaxies. We also measured the two-halo conformity, that is, the correlation in the specific star formation rate between low-mass central galaxies and their neighbors at megaparsec scales, and how former satellites contribute to the signal at three different redshifts: z = 0, 0.3, and 1. The time evolution of the conformity signal in the simulations presents apparent contradictory results: it decreases from z = 0 to z = 1 in MDPL2-SAG, while it increases in TNG300. However, after removing former satellites in the latter, the signal is strongly reduced, but practically does not change at z ≤ 0.3, and it disappears at z = 1. We compare our findings with recent literature data and discuss the conformity measurements, as different approaches can lead to varying results.

Many topics in modern astronomy are characterised by the identification of features in images. While this is an easy task for a trained eye, it is difficult to obtain the same quality when performed by models or numerical methods. This has led to cooperation between research teams and citizenship has a long history in different scientific disciplines, due to the great interest of the public, the presence of amateur associations and the constant need for processing large volumes of data. In this work the objective is to present the experience and development of a citizen science web platform (PISCIS, Platform for Interactive Search and CItizen Science), a platform that aims to generate value-added catalogues from data comprising a set of images making use of the citizen’s interest in Astronomy, facilitating the collection and analysis of data as well as making the public aware of the methodology and research topics in the area of Astronomy. A user-friendly application was created for the pollster and the public to create concise surveys and accompany them with images, along with spaces to add information and examples of the surveys to be carried out. The platform is now available. In addition, it is being used to classify the first set of data, consisting of pairs of galaxies, the objective is to catalogue them according to the type of interaction and, for this, examples of pairs with high, medium or low interaction are provided. The collaboration of the public has been important, both in evaluating the platform and in visually inspecting hundreds of galaxy pairs. PISCIS allows people to be linked to research projects, making it possible for a researcher to collect a large amount of data. In order to be able to perform the classifications, training is necessary, so in turn, the participant also learns about science and how it works.