Osservatorio astronomico di Bologna

Abstract Recent observations from the James Webb Space Telescope have revealed unexpectedly luminous galaxies, exhibiting stellar masses and luminosities significantly higher than predicted by theoretical models at Cosmic Dawn. In this study, we present a suite of cosmological zoomed-in simulations targeting high-redshift ( z ≥ 10) galaxies with dark matter halo masses in the range 10 10 –10 11 M ⊙ at z = 10, using state-of-the-art galaxy formation simulation codes ( Enzo , Ramses , Changa , Gadget-3 , Gadget-4 , and Gizmo ). This study aims to evaluate the convergence of the participating codes and their reproducibility of high-redshift galaxies with the galaxy formation model calibrated at relatively low redshift, without additional physics for high-redshift environments. The subgrid physics follows the AGORA CosmoRun framework, with adjustments to resolution and initial conditions to emulate similar physical environments in the early Universe. The participating codes show consistent results for key galaxy properties (e.g., stellar mass), but also reveal notable differences (e.g., metallicity), indicating that galaxy properties at high redshifts are highly sensitive to the feedback implementation of the simulation. Massive halos ( M halo ≥5 × 10 10 M ⊙ at z = 10) succeed in reproducing observed stellar masses, metallicities, and UV luminosities at 10 ≤ z ≤ 12 without requiring additional subgrid physics, but tend to underpredict those properties at higher redshift. We also find that varying the dust-to-metal ratio modestly affects UV luminosity of simulated galaxies, whereas the absence of dust significantly enhances it. In future work, higher-resolution simulations will be conducted to better understand the formation and evolution of galaxies at Cosmic Dawn.

The Eifel region (southwest Germany) is an intracontinental volcanic field of distributed explosive centers, with the last major eruption occurring at the actively degassing Laacher See volcano in 13ka. The temporary Eifel large-N seismic network was deployed here between September 2022 and August 2023, which significantly increased station coverage allowing for a detailed study of the subsurface magmatic system. We use local earthquakes to study the attenuation properties of the subsurface structure, targeting Laacher See volcano and its surroundings. Starting with an automatically derived earthquake catalog, we first perform a number of quality checks to ensure we only use the cleanest waveform traces and picks. Then, we estimate scattering from peak-delay measurements, i.e. the delay of the maximum energy after the S-wave. Our preliminary findings suggest the presence of two upper crustal structures beneath Laacher See, outlined by areas of high scattering, which are typically associated with the presence of small-scale heterogeneities or mechanical discontinuities (e.g. fractures, faults) and range from the surface to 8 and 13 km below sea level. Their proximity to Laacher See suggests that the rise of fluids may be facilitated by these structures. Further analysis will have to show whether the data can also be used to quantify absorption, which would shed even more light on fluid pathways.

Context. Radio halos are diffuse megaparsec-scale nonthermal radio sources located at the center of galaxy clusters. They trace relativistic particles and magnetic fields in the intra-cluster medium. The source of energy for their formation is believed to be the merging of galaxy clusters, which generates turbulence and reaccelerates aged electrons. Aims. We studied the diffuse radio emission, spectral properties, and the connection between thermal and nonthermal emission in the massive ( M 500 ∼ 7 × 10 14 M ⊙ ), dynamically disturbed galaxy clusters Abell 773 and Abell 1351. Methods. We combined observations from the LOFAR Two-meter Sky Survey Data Release 2 at 144 MHz and the new upgraded Giant Meterwave Radio Telescope at 650 MHz for both clusters. Archival XMM-Newton X-ray images were utilized to supplement our analysis. Results. We confirm that both clusters host a radio halo, each of which has a largest linear size of ∼2 Mpc. We measure an integrated spectral index ($ \alpha_{144}^{650} $) of ∼ − 1.0 for both clusters. Via point-to-point analysis, we show that the radio halo in A773 resembles a classical radio halo that follows a sublinear relation between radio and X-ray surface brightness. Conversely, A1351 exhibits a more complex and asymmetric radio halo that is embedded with several radio sources, including the brightest cluster galaxy, a tail galaxy, and the ridge. We find a deviation from the sublinear relation in the point-to-point analysis that is due to the presence of these contaminating radio sources.

Abstract Accurate neutron capture cross sections are essential for the design and operation of fast reactors using MOX fuels. For $$^{242}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>242</mml:mn> </mml:mmultiscripts> </mml:math> Pu, the Nuclear Energy Agency (NEA) recommends 8–12% accuracy in the fast energy region (2–500 keV), compared to the current uncertainty of 35%. Moreover, integral experiments and previous measurements suggest the evaluated $$^{242}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>242</mml:mn> </mml:mmultiscripts> </mml:math> Pu(n, $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> ) cross section is overestimated, particularly in the JEFF-3.3 library, which shows a 14% overestimation between 1 keV and 1 MeV. Recent measurements from LANSCE reported a 20–30% reduction in the 1–40 keV range relative to evaluations. To solve these discrepancies, the $$^{242}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>242</mml:mn> </mml:mmultiscripts> </mml:math> Pu(n, $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> ) cross section was measured from 1 to 600 keV at CERN n_TOF-EAR1 facility using a 95(4) mg $$^{242}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>242</mml:mn> </mml:mmultiscripts> </mml:math> Pu target, enriched to 99.959%. Gamma rays from neutron capture were detected with an array of $$\hbox {C}_6\hbox {D}_6$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>C</mml:mtext> <mml:mn>6</mml:mn> </mml:msub> <mml:msub> <mml:mtext>D</mml:mtext> <mml:mn>6</mml:mn> </mml:msub> </mml:mrow> </mml:math> scintillators and a novel application of the Pulse Height Weighting Technique was employed. The resulting cross section presents a systematic uncertainty between 8 and 12%, reducing the current uncertainties of 35% and achieving the accuracy requested by the NEA. Analysis using FITACS produced average resonance parameters, consistent with the analysis of the resolved resonance region. Our data align well with Wisshak and Käeppeler, and are 10–14% lower than JEFF-3.3 in the 1–250 keV range, helping to achieve consistency with integral benchmarks. At higher energies, our results are in reasonable agreement with ENDF/B-VIII.1 and JEFF-3.3. In contrast, DANCE results appear to underestimate the cross section by a factor of 2–3 above a few keV.

Context. It is well known that star-forming galaxies (SFGs) exhibit a tight correlation between their radio and infrared emissions, commonly referred to as the infrared-radio correlation (IRRC). Recent empirical studies have reported a dependence of the IRRC on the galaxy stellar mass, in which more massive galaxies tend to show lower infrared-to-radio ratios ( q IR ) with respect to less massive galaxies. One possible, yet unexplored, explanation is a residual contamination of the radio emission from active galactic nuclei (AGNs), not captured through “radio-excess” diagnostics. Aims. To investigate this hypothesis, we aim to statistically quantify the contribution of AGN emission to the radio luminosities of SFGs located within the scatter of the IRRC. Methods. Our Very Large Baseline Array (VLBA) AGN-sCAN program has targeted 500 galaxies that follow the q IR distribution of the IRRC, i.e., with no prior evidence for radio-excess AGN emission based on low-resolution (∼arcsec) VLA radio imaging. Our VLBA 1.4 GHz observations reach a 5 σ sensitivity limit of 25 μJy/beam, corresponding to a radio-brightness temperature of T b ∼ 10 5 K. This classification serves as a robust AGN diagnostic, regardless of the host galaxy’s star formation rate. Results. We detect four VLBA sources in the deepest regions, which are also the faintest VLBI-detected AGNs in SFGs to date. The effective AGN detection rate is 9%, when considering a control sample matched in mass and sensitivity, which is in good agreement with the extrapolation of previous radio AGN number counts. Despite the non-negligible AGN flux contamination (∼30%) in our individual VLBA detections, we find that the peak of the q IR distribution is completely unaffected by this correction. Although we cannot rule out a high incidence of radio-silent AGNs at (sub)μJy levels among the VLBA non-detections, we derive a conservative upper limit of &lt; 0.1 dex of their cumulative impact on the q IR distribution. We conclude that residual AGN contamination from non-radio-excess AGNs is unlikely to be the primary driver of the M ★ – dependent IRRC.

We recently used a large set of Monte Carlo simulations of globular clusters (GCs) to define new fully empirical parameters (named A5, P5, and S2.5) able to trace the internal dynamical evolution of dense stellar systems. These parameters are specifically designed to quantify the steepness of the cumulative radial distribution of stars in the innermost region of the host system, which tends to progressively increase with dynamical aging due to core contraction. Following the original definitions, here we measure A5 and P5 in a sample of 40 Galactic GCs homogeneously surveyed through HST photometric observations. In agreement with the predictions of our simulations, the largest values of A5 and P5 are found for the most dynamically evolved GCs, i.e., those previously classified as post-core collapse systems based on the shape of their density profile, and those characterized by the shortest central relaxation times. Moreover, the new dynamical parameters here measured strongly correlate with A+rh, another fully empirical, independent parameter that traces the dynamical age of star clusters through the level of central segregation of blue straggler stars.

We investigate the redshift evolution and group richness dependence of the quiescent galaxy fraction and red sequence (RS) parameters in COSMOS galaxy groups, spanning a wide redshift range, from z=0 to z=3.7. We analyzed the deep and well-characterized sample of groups recently detected with the AMICO algorithm in the COSMOS(-Web) field. Our study of the quiescent galaxy population is based on a machine-learning classification tool based on rest-frame magnitudes. The algorithm learns from several traditional methods to estimate the probability of a galaxy being quiescent, achieving high precision and recall. Starting from this classification, we computed quiescent galaxy fractions within groups via two methods: one based on the membership probabilities provided by AMICO, which rely on an analytical model, and another using a model-independent technique. We then detected the RS by estimating the ridgeline position using probability-weighted photometric data, followed by σ clipping to remove outliers. This analysis was performed using both rest-frame magnitudes and observer-frame magnitudes with rest-frame matching. We compared the results from both approaches and investigated the redshift and richness dependence of the RS parameters. We found that the quiescent galaxy population in groups builds up steadily from z = 1.5-2 across all richnesses, with faster and earlier growth in the richest groups. The first galaxies settle onto the RS ridgeline by z ∼ 2, consistent with current evolutionary scenarios. Notably, we reported a rare protocluster core hosting quiescent galaxies at z = 3.4, potentially one of the most distant early RSs observed. Extending our study to X-ray properties, we found that X-ray faint groups have, on average, lower quiescent fractions than X-ray bright ones, likely reflecting their typical location in filaments where pre-processing is lower. Leveraging the broad wavelength coverage of COSMOS2025, we traced RS evolution using observed and rest-frame colors over ∼ 12 Gyr, finding no significant trends in either the slope or the scatter of the ridgeline.

An unsupervised machine learning framework is developed for identifying anomalous events in proton–proton collisions at √𝑠 = 13 TeV, trained on the ATLAS Run-2 open dataset collected during 2015–2016. The analysis utilize a model independent approach based on TAB-transformer autoencoder trained to characterize Standard Model event topologies and identify deviations. The anomaly scores show clear separation between background and MC generated beyond-Standard Model and rare benchmark processes. Clustering of high-scoring events reveals distinct kinematic structures consistent with signatures of rare and BSM dynamics. The result demonstrates the sensitivity of the Tab-Transformer-based anomaly detection framework to diverse rare and BSM signatures, enabling data-driven exploration beyond traditional search strategies.

We investigated how the obscured IR-derived and dust-corrected UV star formation rate functions (SFRFs) compare with each other and with predictions from state-of-the-art theoretical models of galaxy formation and evolution. We derived the IR SFRF from the ALMA A3COSMOS survey by converting the IR luminosity functions (IR LFs) into SFRFs after correcting for the active galactic nucleus (AGN) contribution. Similarly, we obtained the UV SFRFs from UV LFs in the literature, corrected for dust-extinction. First, we fit the two SFRFs independently via a Markov chain Monte Carlo (MCMC) approach, then we combined them to obtain the first estimate of the ``total'' SFRF out to z ∼ 6. Finally, we compared this SFRF with predictions of a set of theoretical models. We derive the UV and IR SFRFs at 0.5 &lt; z &lt; 6, using dust-extinction-corrected UV LFs from the literature and IR LFs from and ALMA. We find that the two functions are largely complementary, covering different ranges in star formation rate (SFR$ &lt; 10-100$ M_⊙yr-1 for the UV-corrected, and SFR &gt; 100$ M_⊙yr^-1 for the IR). From the comparison of the total SFRF with model predictions, we find overall good agreement at $z &lt; 2.5, with increasing difference at higher redshifts; all models miss the galaxies that form stars with the highest SFRs. Finally, we finally obtain the UV (dust-corrected), IR and total SFR densities (SFRDs), finding that there are no redshift ranges where UV and IR alone are able to reproduce the total SFRD. Herschel

Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this work, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame λ rest ∼ 3 μm, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most (≳50%) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ( N H &gt; 3 × 10 24 cm −2 ) gas obscuration is common, and likely confined within the dust sublimation radius ( R sub ∼ 0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear.